drop_fpu() and fpu_reset_state() are similar in functionality
and in scope, yet this is not apparent from their names.

drop_fpu() deactivates FPU contents (both the fpregs and the fpstate),
but leaves register contents intact in the eager-FPU case, mostly as an
optimization. It disables fpregs in the lazy FPU case. The drop_fpu()
method can be used to destroy FPU state in an optimized way, when we
know that a new state will be loaded before user-space might see
any remains of the old FPU state:

     - such as in sys_exit()'s exit_thread() where we know this task
       won't execute any user-space instructions anymore and the
       next context switch cleans up the FPU. The old FPU state
       might still be around in the eagerfpu case but won't be
       saved.

     - in __restore_xstate_sig(), where we use drop_fpu() before
       copying a new state into the fpstate and activating that one.
       No user-pace instructions can execute between those steps.

     - in sys_execve()'s fpu__clear(): there we use drop_fpu() in
       the !eagerfpu case, where it's equivalent to a full reinit.

fpu_reset_state() is a stronger version of drop_fpu(): both in
the eagerfpu and the lazy-FPU case it guarantees that fpregs
are reinitialized to init state. This method is used in cases
where we need a full reset:

     - handle_signal() uses fpu_reset_state() to reset the FPU state
       to init before executing a user-space signal handler. While we
       have already saved the original FPU state at this point, and
       always restore the original state, the signal handling code
       still has to do this reinit, because signals may interrupt
       any user-space instruction, and the FPU might be in various
       intermediate states (such as an unbalanced x87 stack) that is
       not immediately usable for general C signal handler code.

     - __restore_xstate_sig() uses fpu_reset_state() when the signal
       frame has no FP context. Since the signal handler may have
       modified the FPU state, it gets reset back to init state.

     - in another branch __restore_xstate_sig() uses fpu_reset_state()
       to handle a restoration error: when restore_user_xstate() fails
       to restore FPU state and we might have inconsistent FPU data,
       fpu_reset_state() is used to reset it back to a known good
       state.

     - __kernel_fpu_end() uses fpu_reset_state() in an error branch.
       This is in a 'must not trigger' error branch, so on bug-free
       kernels this never triggers.

     - fpu__restore() uses fpu_reset_state() in an error path
       as well: if the fpstate was set up with invalid FPU state
       (via ptrace or via a signal handler), then it's reset back
       to init state.

     - likewise, the scheduler's switch_fpu_finish() uses it in a
       restoration error path too.

Move both drop_fpu() and fpu_reset_state() to the fpu__*() namespace
and harmonize their naming with their function:

    fpu__drop()
    fpu__reset()

This clearly shows that both methods operate on the full state of the
FPU, just like fpu__restore().

Also add comments to explain what each function does.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

We'd like to use xsave_state() earlier, but its SYSTEM_BOOTING check
is too imprecise.

The real condition that xsave_state() would like to check is whether
alternative XSAVE instructions were patched into the kernel image
already.

Add such a (read-mostly) debug flag and use it in xsave_state().

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

So prior to this fix:

  c88d4748 ("x86/fpu: Always restore_xinit_state() when use_eager_cpu()")

we leaked FPU state across execve() boundaries on eagerfpu systems:

	$ /host/home/mingo/dump-xmm-regs-exec
	# XMM state before execve():
	XMM0 : 000000000000dede
	XMM1 : 000000000000dedf
	XMM2 : 000000000000dee0
	XMM3 : 000000000000dee1
	XMM4 : 000000000000dee2
	XMM5 : 000000000000dee3
	XMM6 : 000000000000dee4
	XMM7 : 000000000000dee5
	XMM8 : 000000000000dee6
	XMM9 : 000000000000dee7
	XMM10: 000000000000dee8
	XMM11: 000000000000dee9
	XMM12: 000000000000deea
	XMM13: 000000000000deeb
	XMM14: 000000000000deec
	XMM15: 000000000000deed

	# XMM state after execve(), in the new task context:
	XMM0 : 0000000000000000
	XMM1 : 2f2f2f2f2f2f2f2f
	XMM2 : 0000000000000000
	XMM3 : 0000000000000000
	XMM4 : 00000000000000ff
	XMM5 : 00000000ff000000
	XMM6 : 000000000000dee4
	XMM7 : 000000000000dee5
	XMM8 : 0000000000000000
	XMM9 : 0000000000000000
	XMM10: 0000000000000000
	XMM11: 0000000000000000
	XMM12: 0000000000000000
	XMM13: 000000000000deeb
	XMM14: 000000000000deec
	XMM15: 000000000000deed

Better explain what this function is supposed to do and why.
Reviewed-by: NBorislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

FPU fpregs do not get initialized during bootup on secondary CPUs,
on non-xsave capable CPUs.

For example on one of my systems, the secondary CPU has this FPU
state on bootup:

	x86: Booting SMP configuration:
	.... node  #0, CPUs:      #1
	x86/fpu ######################
	x86/fpu # FPU register dump on CPU#1:
	x86/fpu # ... CWD: ffff0040
	x86/fpu # ... SWD: ffff0000
	x86/fpu # ... TWD: ffff555a
	x86/fpu # ... FIP: 00000000
	x86/fpu # ... FCS: 00000000
	x86/fpu # ... FOO: 00000000
	x86/fpu # ... FOS: ffff0000
	x86/fpu # ... FP0: 02 57 00 00 00 00 00 00 ff ff
	x86/fpu # ... FP1: 1b e2 00 00 00 00 00 00 ff ff
	x86/fpu # ... FP2: 00 00 00 00 00 00 00 00 00 00
	x86/fpu # ... FP3: 00 00 00 00 00 00 00 00 00 00
	x86/fpu # ... FP4: 00 00 00 00 00 00 00 00 00 00
	x86/fpu # ... FP5: 00 00 00 00 00 00 00 00 00 00
	x86/fpu # ... FP6: 00 00 00 00 00 00 00 00 00 00
	x86/fpu # ... FP7: 00 00 00 00 00 00 00 00 00 00
	x86/fpu # ...  SW: dadadada
	x86/fpu ######################

Note how CWD and TWD are off their usual init state (0x037f and 0xffff),
and how FP0 and FP1 has non-zero content.

This is normally not a problem, because any user-space FPU state
is initalized properly - but it can complicate the use of FPU
instructions in kernel code via kernel_fpu_begin()/end(): if
the FPU using code does not initialize registers itself, it
might generate spurious exceptions depending on which CPU it
executes on.

Fix this by initializing the x87 state via the FNINIT instruction.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Rename this function in line with the new FPU nomenclature.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

So this function still had ancient language about 'saving current
math information' - but we haven't been doing lazy FPU saves for
quite some time, we are doing lazy FPU restores.

Also remove IRQ13 related comment, which we don't support anymore
either.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Move the naming in line with existing names, so that we now have:

  copy_fpregs_to_fpstate()
  copy_fpstate_to_sigframe()
  copy_fpregs_to_sigframe()

... where each function does what its name suggests.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Standardize the naming of save_xstate_sig() by renaming it to
copy_fpstate_to_sigframe(): this tells us at a glance that
the function copies an FPU fpstate to a signal frame.

This naming also follows the naming of copy_fpregs_to_fpstate().

Don't put 'xstate' into the name: since this is a generic name,
it's expected that the function is able to handle xstate frames
as well, beyond legacy frames.

xstate used to be the odd case in the x86 FPU code - now it's the
common case.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Currently fpstate_sanitize_xstate() has a task_struct input parameter,
but it only uses the fpu structure from it - so pass in a 'struct fpu'
pointer only and update all call sites.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Remove the extra layer of __fpstate_sanitize_xstate():

	if (!use_xsaveopt())
		return;
	__fpstate_sanitize_xstate(tsk);

and move the check for use_xsaveopt() into fpstate_sanitize_xstate().

In general we optimize for the presence of CPU features, not for
the absence of them. Furthermore there's little point in this inlining,
as the call sites are not super hot code paths.

Doing this uninlining shrinks the code a bit:

   text    data     bss     dec     hex filename
   14108751        2573624 1634304 18316679        1177d87 vmlinux.before
   14108627        2573624 1634304 18316555        1177d0b vmlinux.after

Also remove a pointless '!fx' check from fpstate_sanitize_xstate().

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

So the sanitize_i387_state() function has the following purpose:
on CPUs that support optimized xstate saving instructions, an
FPU fpstate might end up having partially uninitialized data.

This function initializes that data.

Note that the function name is a misnomer and confusing on two levels,
not only is it not i387 specific at all, but it is the exact opposite:
it only matters on xstate CPUs.

So rename sanitize_i387_state() and __sanitize_i387_state() to
fpstate_sanitize_xstate() and __fpstate_sanitize_xstate(),
to clearly express the purpose and usage of the function.

We'll further clean up this function in the next patch.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Now that all FPU internals using drivers are converted to public APIs,
move xcr.h's definitions into fpu/internal.h and remove xcr.h.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

This file only uses the public FPU APIs, so remove the xcr.h, fpu/xstate.h
and fpu/internal.h headers and add the fpu/api.h include.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Use the new 'cpu_has_xfeatures()' function to query AVX CPU support.

This has the following advantages to the driver:

 - Decouples the driver from FPU internals: it's now only using <asm/fpu/api.h>.

 - Removes detection complexity from the driver, no more raw XGETBV instruction

 - Shrinks the code a bit.

 - Standardizes feature name error message printouts across drivers

There are also advantages to the x86 FPU code: once all drivers
are decoupled from internals we can move them out of common
headers and we'll also be able to remove xcr.h.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Use the new 'cpu_has_xfeatures()' function to query AVX CPU support.

This has the following advantages to the driver:

 - Decouples the driver from FPU internals: it's now only using <asm/fpu/api.h>.

 - Removes detection complexity from the driver, no more raw XGETBV instruction

 - Shrinks the code a bit.

 - Standardizes feature name error message printouts across drivers

There are also advantages to the x86 FPU code: once all drivers
are decoupled from internals we can move them out of common
headers and we'll also be able to remove xcr.h.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Use the new 'cpu_has_xfeatures()' function to query AVX CPU support.

This has the following advantages to the driver:

 - Decouples the driver from FPU internals: it's now only using <asm/fpu/api.h>.

 - Removes detection complexity from the driver, no more raw XGETBV instruction

 - Shrinks the code a bit.

 - Standardizes feature name error message printouts across drivers

There are also advantages to the x86 FPU code: once all drivers
are decoupled from internals we can move them out of common
headers and we'll also be able to remove xcr.h.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Use the new 'cpu_has_xfeatures()' function to query AVX CPU support.

This has the following advantages to the driver:

 - Decouples the driver from FPU internals: it's now only using <asm/fpu/api.h>.

 - Removes detection complexity from the driver, no more raw XGETBV instruction

 - Shrinks the code a bit.

 - Standardizes feature name error message printouts across drivers

There are also advantages to the x86 FPU code: once all drivers
are decoupled from internals we can move them out of common
headers and we'll also be able to remove xcr.h.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Use the new 'cpu_has_xfeatures()' function to query AVX CPU support.

This has the following advantages to the driver:

 - Decouples the driver from FPU internals: it's now only using <asm/fpu/api.h>.

 - Removes detection complexity from the driver, no more raw XGETBV instruction

 - Shrinks the code a bit.

 - Standardizes feature name error message printouts across drivers

There are also advantages to the x86 FPU code: once all drivers
are decoupled from internals we can move them out of common
headers and we'll also be able to remove xcr.h.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Use the new 'cpu_has_xfeatures()' function to query AVX CPU support.

This has the following advantages to the driver:

 - Decouples the driver from FPU internals: it's now only using <asm/fpu/api.h>.

 - Removes detection complexity from the driver, no more raw XGETBV instruction

 - Shrinks the code a bit.

 - Standardizes feature name error message printouts across drivers

There are also advantages to the x86 FPU code: once all drivers
are decoupled from internals we can move them out of common
headers and we'll also be able to remove xcr.h.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Use the new 'cpu_has_xfeatures()' function to query AVX CPU support.

This has the following advantages to the driver:

 - Decouples the driver from FPU internals: it's now only using <asm/fpu/api.h>.

 - Removes detection complexity from the driver, no more raw XGETBV instruction

 - Shrinks the code a bit.

 - Standardizes feature name error message printouts across drivers

There are also advantages to the x86 FPU code: once all drivers
are decoupled from internals we can move them out of common
headers and we'll also be able to remove xcr.h.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Use the new 'cpu_has_xfeatures()' function to query AVX CPU support.

This has the following advantages to the driver:

 - Decouples the driver from FPU internals: it's now only using <asm/fpu/api.h>.

 - Removes detection complexity from the driver, no more raw XGETBV instruction

 - Shrinks the code a bit.

 - Standardizes feature name error message printouts across drivers

There are also advantages to the x86 FPU code: once all drivers
are decoupled from internals we can move them out of common
headers and we'll also be able to remove xcr.h.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Use the new 'cpu_has_xfeatures()' function to query AVX CPU support.

This has the following advantages to the driver:

 - Decouples the driver from FPU internals: it's now only using <asm/fpu/api.h>.

 - Removes detection complexity from the driver, no more raw XGETBV instruction

 - Shrinks the code a bit.

 - Standardizes feature name error message printouts across drivers

There are also advantages to the x86 FPU code: once all drivers
are decoupled from internals we can move them out of common
headers and we'll also be able to remove xcr.h.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Use the new 'cpu_has_xfeatures()' function to query AVX CPU support.

This has the following advantages to the driver:

 - Decouples the driver from FPU internals: it's now only using <asm/fpu/api.h>.

 - Removes detection complexity from the driver, no more raw XGETBV instruction

 - Shrinks the code a bit:

     text    data     bss     dec     hex filename
     2128    2896       0    5024    13a0 camellia_aesni_avx_glue.o.before
     2067    2896       0    4963    1363 camellia_aesni_avx_glue.o.after

 - Standardizes feature name error message printouts across drivers

There are also advantages to the x86 FPU code: once all drivers
are decoupled from internals we can move them out of common
headers and we'll also be able to remove xcr.h.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

So xsave.h is an internal header that FPU using drivers commonly include,
to get access to the xstate feature names, amongst other things.

Move these type definitions to fpu/fpu.h to allow simplification
of FPU using driver code.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Transform the xstate masks into an enumerated list of xfeature bits.

This removes the hard coding of XFEATURES_NR_MAX.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

We do a boot time printout of xfeatures in print_xstate_features(),
simplify this code to make use of the recently introduced cpu_has_xfeature()
method.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

A lot of FPU using driver code is querying complex CPU features to be
able to figure out whether a given set of xstate features is supported
by the CPU or not.

Introduce a simplified API function that can be used on any CPU type
to get this information. Also add an error string return pointer,
so that the driver can print a meaningful error message with a
standardized feature name.

Also mark xfeatures_mask as __read_only.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

'xsave' is an x86 instruction name to most people - but xsave.h is
about a lot more than just the XSAVE instruction: it includes
definitions and support, both internal and external, related to
xstate and xfeatures support.

As a first step in cleaning up the various xstate uses rename this
header to 'fpu/xstate.h' to better reflect what this header file
is about.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

The current fpu_copy() code on lazy switching CPUs always saves
into the current fpstate and then copies it over into the child
context:

		preempt_disable();
		if (!copy_fpregs_to_fpstate(src_fpu))
			fpregs_deactivate(src_fpu);
		preempt_enable();
		memcpy(&dst_fpu->state, &src_fpu->state, xstate_size);

That memcpy() can be avoided on all lazy switching setups except
really old FNSAVE-only systems: change fpu_copy() to directly save
into the child context, for both the lazy and the eager context
switching case.

Note that we still have to do a memcpy() back into the parent
context in the FNSAVE case, but this won't be executed on the
majority of x86 systems that got built in the last 10 years or so.
Reviewed-by: NBorislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Optimize fpu_copy() a bit by expanding the ->fpstate_active == 1
portion of fpu__save() into it.

( The main purpose of this change is to enable another, larger
  optimization that will be done in the next patch. )
Reviewed-by: NBorislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

So fpu__save() does this currently:

		copy_fpregs_to_fpstate(fpu);
		if (!use_eager_fpu())
			fpregs_deactivate(fpu);

... which deactivates the FPU on lazy switching systems unconditionally.

Both usecases of fpu__save() use this function to save the
FPU state into a fpstate: fork()/clone() and math error signal handling.

The unconditional disabling of FPU registers in the lazy switching
case is probably a mistaken conversion of old FNSAVE code (that had
to disable FPU registers).

So speed up this code by only disabling FPU registers when absolutely
necessary: when indicated by the copy_fpregs_to_fpstate() return
code:

		if (!copy_fpregs_to_fpstate(fpu))
			fpregs_deactivate(fpu);
Reviewed-by: NBorislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Factor out a common call.
Reviewed-by: NBorislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

The current implementation of __save_fpu():

	if (use_xsave()) {
		xsave_state(&fpu->state.xsave);
	} else {
		fpu_fxsave(fpu);
	}

Is actually a simplified version of copy_fpregs_to_fpstate(),
if use_eager_fpu() is true.

But all call sites of __save_fpu() call it only it when use_eager_fpu()
is true.

So we can eliminate __save_fpu() altogether and use the standard
copy_fpregs_to_fpstate() function. This cleans up the code
by making it use fewer variants of FPU register saving.
Reviewed-by: NBorislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

__save_fpu() has this pattern:

		if (unlikely(system_state == SYSTEM_BOOTING))
			xsave_state_booting(&fpu->state.xsave);
		else
			xsave_state(&fpu->state.xsave);

... but it does not actually get called during system bootup.

So remove the complication and always call xsave_state().

To make sure this assumption is correct, add a WARN_ONCE()
debug check to xsave_state().
Reviewed-by: NBorislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

We have repeat patterns of:

	if (!use_eager_fpu())
		clts();

... to activate FPU registers, and:

	if (!use_eager_fpu())
		stts();

... to deactivate them.

Encapsulate these in:

	__fpregs_activate_hw();
	__fpregs_activate_hw();

and use them accordingly.

Doing this synchronizes the idiom with the fpu->fpregs_active
software-flag's handling functions, creating clear patterns of:

	__fpregs_activate_hw();
	__fpregs_activate(fpu);

etc., which improves readability.
Reviewed-by: NBorislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

In line with the fpstate_activate() change, name
fpu__unlazy_stopped() in a similar fashion as well: its purpose
is to make the fpstate of a stopped task the current and active FPU
context, which may require unlazying and initialization.

The unlazying is just part of the job, the main concept is to make
the fpstate active.

Also clarify the function's description to clarify its exact
usage and the background behind it all.
Reviewed-by: NBorislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Now that fpstate_init_curr() is not doing implicit allocations
anymore, almost all uses of it involve a very simple pattern:

	if (!fpu->fpstate_active)
		fpstate_init_curr(fpu);

which is basically activating the FPU fpstate if it was not active
before.

So propagate the check into the function itself, and rename the
function according to its new purpose:

	fpu__activate_curr(fpu);
Reviewed-by: NBorislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Now that fpstate_init() cannot fail the error return of fx_init()
has lost its purpose. Eliminate the error return and propagate this
change to all callers.
Reviewed-by: NBorislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Now that FPU contexts are always allocated, fpu__unlazy_stopped()
cannot fail. Remove its error return and propagate the changes to
the callers.
Reviewed-by: NBorislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>