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  1. 05 3月, 2012 7 次提交
  3. 27 2月, 2012 2 次提交
  5. 24 2月, 2012 7 次提交
  7. 22 2月, 2012 6 次提交
    • B
      x86/mce/AMD: Fix UP build error · 3f806e50
      由 Borislav Petkov 提交于 
      141168c3 ("x86: Simplify code by removing a !SMP #ifdefs
from 'struct cpuinfo_x86'") removed a bunch of CONFIG_SMP ifdefs
around code touching struct cpuinfo_x86 members but also caused
the following build error with Randy's randconfigs:

mce_amd.c:(.cpuinit.text+0x4723): undefined reference to `cpu_llc_shared_map'

Restore the #ifdef in threshold_create_bank() which creates
symlinks on the non-BSP CPUs.

There's a better patch series being worked on by Kevin Winchester
which will solve this in a cleaner fashion, but that series is
too ambitious for v3.3 merging - so we first queue up this trivial
fix and then do the rest for v3.4.
Signed-off-by: NBorislav Petkov <bp@alien8.de>
Acked-by: NKevin Winchester <kjwinchester@gmail.com>
Cc: Randy Dunlap <rdunlap@xenotime.net>
Cc: Nick Bowler <nbowler@elliptictech.com>
Link: http://lkml.kernel.org/r/20120203191801.GA2846@x1.osrc.amd.comSigned-off-by: NIngo Molnar <mingo@elte.hu>
      3f806e50
    • B
      powerpc: Fix various issues with return to userspace · 18b246fa
      由 Benjamin Herrenschmidt 提交于 
      We have a few problems when returning to userspace. This is a
quick set of fixes for 3.3, I'll look into a more comprehensive
rework for 3.4. This fixes:

 - We kept interrupts soft-disabled when schedule'ing or calling
do_signal when returning to userspace as a result of a hardware
interrupt.

 - Rename do_signal to do_notify_resume like all other archs (and
do_signal_pending back to do_signal, which it was before Roland
changed it).

 - Add the missing call to key_replace_session_keyring() to
do_notify_resume().
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>
---
      18b246fa
    • M
      powerpc: Fix program check handling when lockdep is enabled · 922b9f86
      由 Michael Ellerman 提交于 
      In commit 54321242 ("Disable interrupts early in Program Check"), we
switched from enabling to disabling interrupts in program_check_common.

Whereas ENABLE_INTS leaves r3 untouched, if lockdep is enabled DISABLE_INTS
calls into lockdep code and will clobber r3. That means we pass a bogus
struct pt_regs* into program_check_exception() and all hell breaks loose.

So load our regs pointer into r3 after we call DISABLE_INTS.
Signed-off-by: NMichael Ellerman <michael@ellerman.id.au>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>
      922b9f86
    • R
      powerpc: Remove references to cpu_*_map · 07d2f1a5
      由 Rusty Russell 提交于 
      This has been obsolescent for a while; time for the final push.

In adjacent context, replaced old cpus_* with cpumask_*.
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>
      07d2f1a5
    • L
      sys_poll: fix incorrect type for 'timeout' parameter · faf30900
      由 Linus Torvalds 提交于 
      The 'poll()' system call timeout parameter is supposed to be 'int', not
'long'.

Now, the reason this matters is that right now 32-bit compat mode is
broken on at least x86-64, because the 32-bit code just calls
'sys_poll()' directly on x86-64, and the 32-bit argument will have been
zero-extended, turning a signed 'int' into a large unsigned 'long'
value.

We could just introduce a 'compat_sys_poll()' function for this, and
that may eventually be what we have to do, but since the actual standard
poll() semantics is *supposed* to be 'int', and since at least on x86-64
glibc sign-extends the argument before invocing the system call (so
nobody can actually use a 64-bit timeout value in user space _anyway_,
even in 64-bit binaries), the simpler solution would seem to be to just
fix the definition of the system call to match what it should have been
from the very start.

If it turns out that somebody somehow circumvents the user-level libc
64-bit sign extension and actually uses a large unsigned 64-bit timeout
despite that not being how poll() is supposed to work, we will need to
do the compat_sys_poll() approach.
Reported-by: NThomas Meyer <thomas@m3y3r.de>
Acked-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      faf30900
    • E
      ARM/audit: include audit header and fix audit arch · 5180bb39
      由 Eric Paris 提交于 
      Both bugs being fixed were introduced in:
29ef73b7

Include linux/audit.h to fix below build errors:

  CC      arch/arm/kernel/ptrace.o
arch/arm/kernel/ptrace.c: In function 'syscall_trace':
arch/arm/kernel/ptrace.c:919: error: implicit declaration of function 'audit_syscall_exit'
arch/arm/kernel/ptrace.c:921: error: implicit declaration of function 'audit_syscall_entry'
arch/arm/kernel/ptrace.c:921: error: 'AUDIT_ARCH_ARMEB' undeclared (first use in this function)
arch/arm/kernel/ptrace.c:921: error: (Each undeclared identifier is reported only once
arch/arm/kernel/ptrace.c:921: error: for each function it appears in.)
make[1]: *** [arch/arm/kernel/ptrace.o] Error 1
make: *** [arch/arm/kernel] Error 2

This part of the patch is:
Reported-by: NAxel Lin <axel.lin@gmail.com>
Reported-by: NPeter Ujfalusi <peter.ujfalusi@ti.com>
(They both provided patches to fix it)

This patch also (at the request of the list) fixes the fact that
ARM has both LE and BE versions however the audit code was called as if
it was always BE.  If audit userspace were to try to interpret the bits
it got from a LE system it would obviously do so incorrectly.  Fix this
by using the right arch flag on the right system.

This part of the patch is:
Reported-by: NRussell King - ARM Linux <linux@arm.linux.org.uk>
Signed-off-by: NEric Paris <eparis@redhat.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>
      5180bb39
  9. 21 2月, 2012 8 次提交
    • R
      ARM: OMAP: fix voltage domain build errors with PM_OPP disabled · 3ddd4d0c
      由 Russell King 提交于 
      The voltage domain code wants the voltage tables, which are in the
opp*.c files.  These files aren't built when PM_OPP is disabled,
causing the following build errors at link time:

twl-common.c:(.init.text+0x2e48): undefined reference to `omap34xx_vddmpu_volt_data'
twl-common.c:(.init.text+0x2e4c): undefined reference to `omap34xx_vddcore_volt_data'
twl-common.c:(.init.text+0x2e5c): undefined reference to `omap36xx_vddmpu_volt_data'
twl-common.c:(.init.text+0x2e60): undefined reference to `omap36xx_vddcore_volt_data'
twl-common.c:(.init.text+0x2830): undefined reference to `omap44xx_vdd_mpu_volt_data'
twl-common.c:(.init.text+0x283c): undefined reference to `omap44xx_vdd_iva_volt_data'
twl-common.c:(.init.text+0x2844): undefined reference to `omap44xx_vdd_core_volt_data'
Acked-by: NKevin Hilman <khilman@ti.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>
      3ddd4d0c
    • M
      ARM/PCI: Remove ARM's duplicate definition of 'pcibios_max_latency' · e23e8c06
      由 Myron Stowe 提交于 
      The patch series to re-factor PCI's 'latency timer' setup (re:
http://marc.info/?l=linux-kernel&m=131983853831049&w=2) forgot to
remove the ARM specific definition of 'pcibios_max_latency' once such
had been moved into the pci core resulting in ARM related compile
errors -
  drivers/built-in.o:(.data+0x230): multiple definition of
  `pcibios_max_latency'
  arch/arm/common/built-in.o:(.data+0x40c): first defined here
  make[1]: *** [vmlinux.o] Error 1

In the series, patch 2/16 (commit 168c8619) converted the ARM
specific version of 'pcibios_set_master()' to a non-inlined version.
This was done in preperation for hosting it up into PCI's core, which
was done in patch 10/16 (commit 96c55900) of the series (and
where the removal of ARM's 'pcibios_max_latency' was overlooked).
Reported-by: NRussell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: NMyron Stowe <myron.stowe@redhat.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>
      e23e8c06
    • S
      ARM: 7336/1: smp_twd: Don't register CPUFREQ notifiers if local timers are not initialised · 910ba598
      由 Santosh Shilimkar 提交于 
      Current ARM local timer code registers CPUFREQ notifiers even in case
the twd_timer_setup() isn't called. That seems to be wrong and
would eventually lead to kernel crash on the CPU frequency transitions
on the SOCs where the local timer doesn't exist or broken because of
hardware BUG. Fix it by testing twd_evt and *__this_cpu_ptr(twd_evt).

The issue was observed with v3.3-rc3 and building an OMAP2+ kernel
on OMAP3 SOC which doesn't have TWD.

Below is the dump for reference :

 Unable to handle kernel paging request at virtual address 007e900
 pgd = cdc20000
 [007e9000] *pgd=00000000
 Internal error: Oops: 5 [#1] SMP
 Modules linked in:
 CPU: 0    Not tainted  (3.3.0-rc3-pm+debug+initramfs #9)
 PC is at twd_update_frequency+0x34/0x48
 LR is at twd_update_frequency+0x10/0x48
 pc : [<c001382c>]    lr : [<c0013808>]    psr: 60000093
 sp : ce311dd8  ip : 00000000  fp : 00000000
 r10: 00000000  r9 : 00000001  r8 : ce310000
 r7 : c0440458  r6 : c00137f8  r5 : 00000000  r4 : c0947a74
 r3 : 00000000  r2 : 007e9000  r1 : 00000000  r0 : 00000000
 Flags: nZCv  IRQs off  FIQs on  Mode SVC_32  ISA ARM  Segment usr
 Control: 10c5387d  Table: 8dc20019  DAC: 00000015
 Process sh (pid: 599, stack limit = 0xce3102f8)
 Stack: (0xce311dd8 to 0xce312000)
 1dc0:                                                       6000c
 1de0: 00000001 00000002 00000000 00000000 00000000 00000000 00000
 1e00: ffffffff c093d8f0 00000000 ce311ebc 00000001 00000001 ce310
 1e20: c001386c c0437c4c c0e95b60 c0e95ba8 00000001 c0e95bf8 ffff4
 1e40: 00000000 00000000 c005ef74 ce310000 c0435cf0 ce311ebc 00000
 1e60: ce352b40 0007a120 c08d5108 c08ba040 c08ba040 c005f030 00000
 1e80: c08bc554 c032fe2c 0007a120 c08d4b64 ce352b40 c08d8618 ffff8
 1ea0: c08ba040 c033364c ce311ecc c0433b50 00000002 ffffffea c0330
 1ec0: 0007a120 0007a120 22222201 00000000 22222222 00000000 ce357
 1ee0: ce3d6000 cdc2aed8 ce352ba0 c0470164 00000002 c032f47c 00034
 1f00: c0331cac ce352b40 00000007 c032f6d0 ce352bbc 0003d090 c0930
 1f20: c093d8bc c03306a4 00000007 ce311f80 00000007 cdc2aec0 ce358
 1f40: ce8d20c0 00000007 b6fe5000 ce311f80 00000007 ce310000 0000c
 1f60: c000de74 ce987400 ce8d20c0 b6fe5000 00000000 00000000 0000c
 1f80: 00000000 00000000 001fbac8 00000000 00000007 001fbac8 00004
 1fa0: c000df04 c000dd60 00000007 001fbac8 00000001 b6fe5000 00000
 1fc0: 00000007 001fbac8 00000007 00000004 b6fe5000 00000000 00202
 1fe0: 00000000 beb565f8 00101ffc 00008e8c 60000010 00000001 00000
 [<c001382c>] (twd_update_frequency+0x34/0x48) from [<c008ac4c>] )
 [<c008ac4c>] (smp_call_function_single+0x17c/0x1c8) from [<c0013)
 [<c0013890>] (twd_cpufreq_transition+0x24/0x30) from [<c0437c4c>)
 [<c0437c4c>] (notifier_call_chain+0x44/0x84) from [<c005efe4>] ()
 [<c005efe4>] (__srcu_notifier_call_chain+0x70/0xa4) from [<c005f)
 [<c005f030>] (srcu_notifier_call_chain+0x18/0x20) from [<c032fe2)
 [<c032fe2c>] (cpufreq_notify_transition+0xc8/0x1b0) from [<c0333)
 [<c033364c>] (omap_target+0x1b4/0x28c) from [<c032f47c>] (__cpuf)
 [<c032f47c>] (__cpufreq_driver_target+0x50/0x64) from [<c0331d24)
 [<c0331d24>] (cpufreq_set+0x78/0x98) from [<c032f6d0>] (store_sc)
 [<c032f6d0>] (store_scaling_setspeed+0x5c/0x74) from [<c03306a4>)
 [<c03306a4>] (store+0x58/0x74) from [<c014d868>] (sysfs_write_fi)
 [<c014d868>] (sysfs_write_file+0x80/0xb4) from [<c00f2c2c>] (vfs)
 [<c00f2c2c>] (vfs_write+0xa8/0x138) from [<c00f2e9c>] (sys_write)
 [<c00f2e9c>] (sys_write+0x40/0x6c) from [<c000dd60>] (ret_fast_s)
 Code: e594300c e792210c e1a01000 e5840004 (e7930002)
 ---[ end trace 5da3b5167c1ecdda ]---
Reported-by: NKevin Hilman <khilman@ti.com>
Acked-by: NMarc Zyngier <marc.zyngier@arm.com>
Tested-by: NKevin Hilman <khilman@ti.com>
Signed-off-by: NSantosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>
      910ba598
    • L
      i387: export 'fpu_owner_task' per-cpu variable · 27e74da9
      由 Linus Torvalds 提交于 
      (And define it properly for x86-32, which had its 'current_task'
declaration in separate from x86-64)

Bitten by my dislike for modules on the machines I use, and the fact
that apparently nobody else actually wanted to test the patches I sent
out.

Snif. Nobody else cares.

Anyway, we probably should uninline the 'kernel_fpu_begin()' function
that is what modules actually use and that references this, but this is
the minimal fix for now.
Reported-by: NJosh Boyer <jwboyer@gmail.com>
Reported-and-tested-by: NJongman Heo <jongman.heo@samsung.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      27e74da9
    • S
      x86: Specify a size for the cmp in the NMI handler · a38449ef
      由 Steven Rostedt 提交于 
      Linus noticed that the cmp used to check if the code segment is
__KERNEL_CS or not did not specify a size. Perhaps it does not matter
as H. Peter Anvin noted that user space can not set the bottom two
bits of the %cs register. But it's best not to let the assembly choose
and change things between different versions of gas, but instead just
pick the size.

Four bytes are used to compare the saved code segment against
__KERNEL_CS. Perhaps this might mess up Xen, but we can fix that when
the time comes.

Also I noticed that there was another non-specified cmp that checks
the special stack variable if it is 1 or 0. This too probably doesn't
matter what cmp is used, but this patch uses cmpl just to make it non
ambiguous.

Link: http://lkml.kernel.org/r/CA+55aFxfAn9MWRgS3O5k2tqN5ys1XrhSFVO5_9ZAoZKDVgNfGA@mail.gmail.comSuggested-by: NLinus Torvalds <torvalds@linux-foundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>
      a38449ef
    • L
      i387: support lazy restore of FPU state · 7e16838d
      由 Linus Torvalds 提交于 
      This makes us recognize when we try to restore FPU state that matches
what we already have in the FPU on this CPU, and avoids the restore
entirely if so.

To do this, we add two new data fields:

 - a percpu 'fpu_owner_task' variable that gets written any time we
   update the "has_fpu" field, and thus acts as a kind of back-pointer
   to the task that owns the CPU.  The exception is when we save the FPU
   state as part of a context switch - if the save can keep the FPU
   state around, we leave the 'fpu_owner_task' variable pointing at the
   task whose FP state still remains on the CPU.

 - a per-thread 'last_cpu' field, that indicates which CPU that thread
   used its FPU on last.  We update this on every context switch
   (writing an invalid CPU number if the last context switch didn't
   leave the FPU in a lazily usable state), so we know that *that*
   thread has done nothing else with the FPU since.

These two fields together can be used when next switching back to the
task to see if the CPU still matches: if 'fpu_owner_task' matches the
task we are switching to, we know that no other task (or kernel FPU
usage) touched the FPU on this CPU in the meantime, and if the current
CPU number matches the 'last_cpu' field, we know that this thread did no
other FP work on any other CPU, so the FPU state on the CPU must match
what was saved on last context switch.

In that case, we can avoid the 'f[x]rstor' entirely, and just clear the
CR0.TS bit.
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      7e16838d
    • L
      i387: use 'restore_fpu_checking()' directly in task switching code · 80ab6f1e
      由 Linus Torvalds 提交于 
      This inlines what is usually just a couple of instructions, but more
importantly it also fixes the theoretical error case (can that FPU
restore really ever fail? Maybe we should remove the checking).

We can't start sending signals from within the scheduler, we're much too
deep in the kernel and are holding the runqueue lock etc.  So don't
bother even trying.
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      80ab6f1e
    • L
      i387: fix up some fpu_counter confusion · cea20ca3
      由 Linus Torvalds 提交于 
      This makes sure we clear the FPU usage counter for newly created tasks,
just so that we start off in a known state (for example, don't try to
preload the FPU state on the first task switch etc).

It also fixes a thinko in when we increment the fpu_counter at task
switch time, introduced by commit 34ddc81a ("i387: re-introduce FPU
state preloading at context switch time").  We should increment the
*new* task fpu_counter, not the old task, and only if we decide to use
that state (whether lazily or preloaded).
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      cea20ca3
  11. 20 2月, 2012 3 次提交
    • K
      xen/pat: Disable PAT support for now. · 8eaffa67
      由 Konrad Rzeszutek Wilk 提交于 
      [Pls also look at https://lkml.org/lkml/2012/2/10/228]

Using of PAT to change pages from WB to WC works quite nicely.
Changing it back to WB - not so much. The crux of the matter is
that the code that does this (__page_change_att_set_clr) has only
limited information so when it tries to the change it gets
the "raw" unfiltered information instead of the properly filtered one -
and the "raw" one tell it that PSE bit is on (while infact it
is not).  As a result when the PTE is set to be WB from WC, we get
tons of:

:WARNING: at arch/x86/xen/mmu.c:475 xen_make_pte+0x67/0xa0()
:Hardware name: HP xw4400 Workstation
.. snip..
:Pid: 27, comm: kswapd0 Tainted: G        W    3.2.2-1.fc16.x86_64 #1
:Call Trace:
: [<ffffffff8106dd1f>] warn_slowpath_common+0x7f/0xc0
: [<ffffffff8106dd7a>] warn_slowpath_null+0x1a/0x20
: [<ffffffff81005a17>] xen_make_pte+0x67/0xa0
: [<ffffffff810051bd>] __raw_callee_save_xen_make_pte+0x11/0x1e
: [<ffffffff81040e15>] ? __change_page_attr_set_clr+0x9d5/0xc00
: [<ffffffff8114c2e8>] ? __purge_vmap_area_lazy+0x158/0x1d0
: [<ffffffff8114cca5>] ? vm_unmap_aliases+0x175/0x190
: [<ffffffff81041168>] change_page_attr_set_clr+0x128/0x4c0
: [<ffffffff81041542>] set_pages_array_wb+0x42/0xa0
: [<ffffffff8100a9b2>] ? check_events+0x12/0x20
: [<ffffffffa0074d4c>] ttm_pages_put+0x1c/0x70 [ttm]
: [<ffffffffa0074e98>] ttm_page_pool_free+0xf8/0x180 [ttm]
: [<ffffffffa0074f78>] ttm_pool_mm_shrink+0x58/0x90 [ttm]
: [<ffffffff8112ba04>] shrink_slab+0x154/0x310
: [<ffffffff8112f17a>] balance_pgdat+0x4fa/0x6c0
: [<ffffffff8112f4b8>] kswapd+0x178/0x3d0
: [<ffffffff815df134>] ? __schedule+0x3d4/0x8c0
: [<ffffffff81090410>] ? remove_wait_queue+0x50/0x50
: [<ffffffff8112f340>] ? balance_pgdat+0x6c0/0x6c0
: [<ffffffff8108fb6c>] kthread+0x8c/0xa0

for every page. The proper fix for this is has been posted
and is https://lkml.org/lkml/2012/2/10/228
"x86/cpa: Use pte_attrs instead of pte_flags on CPA/set_p.._wb/wc operations."
along with a detailed description of the problem and solution.

But since that posting has gone nowhere I am proposing
this band-aid solution so that at least users don't get
the page corruption (the pages that are WC don't get changed to WB
and end up being recycled for filesystem or other things causing
mysterious crashes).

The negative impact of this patch is that users of WC flag
(which are InfiniBand, radeon, nouveau drivers) won't be able
to set that flag - so they are going to see performance degradation.
But stability is more important here.

Fixes RH BZ# 742032, 787403, and 745574
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
      8eaffa67
    • K
      xen/setup: Remove redundant filtering of PTE masks. · 416d7214
      由 Konrad Rzeszutek Wilk 提交于 
      commit 7347b408 "xen: Allow
unprivileged Xen domains to create iomap pages" added a redundant
line in the early bootup code to filter out the PTE. That
filtering is already done a bit earlier so this extra processing
is not required.
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
      416d7214
    • S
      x86/nmi: Test saved %cs in NMI to determine nested NMI case · 45d5a168
      由 Steven Rostedt 提交于 
      Currently, the NMI handler tests if it is nested by checking the
special variable saved on the stack (set during NMI handling)
and whether the saved stack is the NMI stack as well (to prevent
the race when the variable is set to zero).

But userspace may set their %rsp to any value as long as they do
not derefence it, and it may make it point to the NMI stack,
which will prevent NMIs from triggering while the userspace app
is running. (I tested this, and it is indeed the case)

Add another check to determine nested NMIs by looking at the
saved %cs (code segment register) and making sure that it is the
kernel code segment.
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: <stable@kernel.org>
Link: http://lkml.kernel.org/r/1329687817.1561.27.camel@acer.local.homeSigned-off-by: NIngo Molnar <mingo@elte.hu>
      45d5a168
  13. 19 2月, 2012 2 次提交
    • L
      i387: re-introduce FPU state preloading at context switch time · 34ddc81a
      由 Linus Torvalds 提交于 
      After all the FPU state cleanups and finally finding the problem that
caused all our FPU save/restore problems, this re-introduces the
preloading of FPU state that was removed in commit b3b0870e ("i387:
do not preload FPU state at task switch time").

However, instead of simply reverting the removal, this reimplements
preloading with several fixes, most notably

 - properly abstracted as a true FPU state switch, rather than as
   open-coded save and restore with various hacks.

   In particular, implementing it as a proper FPU state switch allows us
   to optimize the CR0.TS flag accesses: there is no reason to set the
   TS bit only to then almost immediately clear it again.  CR0 accesses
   are quite slow and expensive, don't flip the bit back and forth for
   no good reason.

 - Make sure that the same model works for both x86-32 and x86-64, so
   that there are no gratuitous differences between the two due to the
   way they save and restore segment state differently due to
   architectural differences that really don't matter to the FPU state.

 - Avoid exposing the "preload" state to the context switch routines,
   and in particular allow the concept of lazy state restore: if nothing
   else has used the FPU in the meantime, and the process is still on
   the same CPU, we can avoid restoring state from memory entirely, just
   re-expose the state that is still in the FPU unit.

   That optimized lazy restore isn't actually implemented here, but the
   infrastructure is set up for it.  Of course, older CPU's that use
   'fnsave' to save the state cannot take advantage of this, since the
   state saving also trashes the state.

In other words, there is now an actual _design_ to the FPU state saving,
rather than just random historical baggage.  Hopefully it's easier to
follow as a result.
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      34ddc81a
    • L
      i387: move TS_USEDFPU flag from thread_info to task_struct · f94edacf
      由 Linus Torvalds 提交于 
      This moves the bit that indicates whether a thread has ownership of the
FPU from the TS_USEDFPU bit in thread_info->status to a word of its own
(called 'has_fpu') in task_struct->thread.has_fpu.

This fixes two independent bugs at the same time:

 - changing 'thread_info->status' from the scheduler causes nasty
   problems for the other users of that variable, since it is defined to
   be thread-synchronous (that's what the "TS_" part of the naming was
   supposed to indicate).

   So perfectly valid code could (and did) do

	ti->status |= TS_RESTORE_SIGMASK;

   and the compiler was free to do that as separate load, or and store
   instructions.  Which can cause problems with preemption, since a task
   switch could happen in between, and change the TS_USEDFPU bit. The
   change to TS_USEDFPU would be overwritten by the final store.

   In practice, this seldom happened, though, because the 'status' field
   was seldom used more than once, so gcc would generally tend to
   generate code that used a read-modify-write instruction and thus
   happened to avoid this problem - RMW instructions are naturally low
   fat and preemption-safe.

 - On x86-32, the current_thread_info() pointer would, during interrupts
   and softirqs, point to a *copy* of the real thread_info, because
   x86-32 uses %esp to calculate the thread_info address, and thus the
   separate irq (and softirq) stacks would cause these kinds of odd
   thread_info copy aliases.

   This is normally not a problem, since interrupts aren't supposed to
   look at thread information anyway (what thread is running at
   interrupt time really isn't very well-defined), but it confused the
   heck out of irq_fpu_usable() and the code that tried to squirrel
   away the FPU state.

   (It also caused untold confusion for us poor kernel developers).

It also turns out that using 'task_struct' is actually much more natural
for most of the call sites that care about the FPU state, since they
tend to work with the task struct for other reasons anyway (ie
scheduling).  And the FPU data that we are going to save/restore is
found there too.

Thanks to Arjan Van De Ven <arjan@linux.intel.com> for pointing us to
the %esp issue.

Cc: Arjan van de Ven <arjan@linux.intel.com>
Reported-and-tested-by: NRaphael Prevost <raphael@buro.asia>
Acked-and-tested-by: NSuresh Siddha <suresh.b.siddha@intel.com>
Tested-by: NPeter Anvin <hpa@zytor.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      f94edacf
  15. 17 2月, 2012 5 次提交