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  1. 19 2月, 2015 2 次提交
  3. 02 2月, 2015 1 次提交
  5. 01 2月, 2015 3 次提交
    • A
      x86_64, entry: Remove the syscall exit audit and schedule optimizations · 96b6352c
      由 Andy Lutomirski 提交于 
      We used to optimize rescheduling and audit on syscall exit.  Now
that the full slow path is reasonably fast, remove these
optimizations.  Syscall exit auditing is now handled exclusively by
syscall_trace_leave.

This adds something like 10ns to the previously optimized paths on
my computer, presumably due mostly to SAVE_REST / RESTORE_REST.

I think that we should eventually replace both the syscall and
non-paranoid interrupt exit slow paths with a pair of C functions
along the lines of the syscall entry hooks.

Link: http://lkml.kernel.org/r/22f2aa4a0361707a5cfb1de9d45260b39965dead.1421453410.git.luto@amacapital.netAcked-by: NBorislav Petkov <bp@suse.de>
Signed-off-by: NAndy Lutomirski <luto@amacapital.net>
      96b6352c
    • A
      x86_64, entry: Use sysret to return to userspace when possible · 2a23c6b8
      由 Andy Lutomirski 提交于 
      The x86_64 entry code currently jumps through complex and
inconsistent hoops to try to minimize the impact of syscall exit
work.  For a true fast-path syscall, almost nothing needs to be
done, so returning is just a check for exit work and sysret.  For a
full slow-path return from a syscall, the C exit hook is invoked if
needed and we join the iret path.

Using iret to return to userspace is very slow, so the entry code
has accumulated various special cases to try to do certain forms of
exit work without invoking iret.  This is error-prone, since it
duplicates assembly code paths, and it's dangerous, since sysret
can malfunction in interesting ways if used carelessly.  It's
also inefficient, since a lot of useful cases aren't optimized
and therefore force an iret out of a combination of paranoia and
the fact that no one has bothered to write even more asm code
to avoid it.

I would argue that this approach is backwards.  Rather than trying
to avoid the iret path, we should instead try to make the iret path
fast.  Under a specific set of conditions, iret is unnecessary.  In
particular, if RIP==RCX, RFLAGS==R11, RIP is canonical, RF is not
set, and both SS and CS are as expected, then
movq 32(%rsp),%rsp;sysret does the same thing as iret.  This set of
conditions is nearly always satisfied on return from syscalls, and
it can even occasionally be satisfied on return from an irq.

Even with the careful checks for sysret applicability, this cuts
nearly 80ns off of the overhead from syscalls with unoptimized exit
work.  This includes tracing and context tracking, and any return
that invokes KVM's user return notifier.  For example, the cost of
getpid with CONFIG_CONTEXT_TRACKING_FORCE=y drops from ~360ns to
~280ns on my computer.

This may allow the removal and even eventual conversion to C
of a respectable amount of exit asm.

This may require further tweaking to give the full benefit on Xen.

It may be worthwhile to adjust signal delivery and exec to try hit
the sysret path.

This does not optimize returns to 32-bit userspace.  Making the same
optimization for CS == __USER32_CS is conceptually straightforward,
but it will require some tedious code to handle the differences
between sysretl and sysexitl.

Link: http://lkml.kernel.org/r/71428f63e681e1b4aa1a781e3ef7c27f027d1103.1421453410.git.luto@amacapital.netSigned-off-by: NAndy Lutomirski <luto@amacapital.net>
      2a23c6b8
    • A
      x86, traps: Fix ist_enter from userspace · b926e6f6
      由 Andy Lutomirski 提交于 
      context_tracking_user_exit() has no effect if in_interrupt() returns true,
so ist_enter() didn't work.  Fix it by calling exception_enter(), and thus
context_tracking_user_exit(), before incrementing the preempt count.

This also adds an assertion that will catch the problem reliably if
CONFIG_PROVE_RCU=y to help prevent the bug from being reintroduced.

Link: http://lkml.kernel.org/r/261ebee6aee55a4724746d0d7024697013c40a08.1422709102.git.luto@amacapital.net
Fixes: 95927475 x86, traps: Track entry into and exit from IST context
Reported-and-tested-by: NSasha Levin <sasha.levin@oracle.com>
Signed-off-by: NAndy Lutomirski <luto@amacapital.net>
      b926e6f6
  7. 30 1月, 2015 2 次提交
    • R
      KVM: x86: check LAPIC presence when building apic_map · df04d1d1
      由 Radim Krčmář 提交于 
      We forgot to re-check LAPIC after splitting the loop in commit
173beedc (KVM: x86: Software disabled APIC should still deliver
NMIs, 2014-11-02).
Signed-off-by: NRadim Krčmář <rkrcmar@redhat.com>
Fixes: 173beedcSigned-off-by: NPaolo Bonzini <pbonzini@redhat.com>
      df04d1d1
    • L
      vm: add VM_FAULT_SIGSEGV handling support · 33692f27
      由 Linus Torvalds 提交于 
      The core VM already knows about VM_FAULT_SIGBUS, but cannot return a
"you should SIGSEGV" error, because the SIGSEGV case was generally
handled by the caller - usually the architecture fault handler.

That results in lots of duplication - all the architecture fault
handlers end up doing very similar "look up vma, check permissions, do
retries etc" - but it generally works.  However, there are cases where
the VM actually wants to SIGSEGV, and applications _expect_ SIGSEGV.

In particular, when accessing the stack guard page, libsigsegv expects a
SIGSEGV.  And it usually got one, because the stack growth is handled by
that duplicated architecture fault handler.

However, when the generic VM layer started propagating the error return
from the stack expansion in commit fee7e49d ("mm: propagate error
from stack expansion even for guard page"), that now exposed the
existing VM_FAULT_SIGBUS result to user space.  And user space really
expected SIGSEGV, not SIGBUS.

To fix that case, we need to add a VM_FAULT_SIGSEGV, and teach all those
duplicate architecture fault handlers about it.  They all already have
the code to handle SIGSEGV, so it's about just tying that new return
value to the existing code, but it's all a bit annoying.

This is the mindless minimal patch to do this.  A more extensive patch
would be to try to gather up the mostly shared fault handling logic into
one generic helper routine, and long-term we really should do that
cleanup.

Just from this patch, you can generally see that most architectures just
copied (directly or indirectly) the old x86 way of doing things, but in
the meantime that original x86 model has been improved to hold the VM
semaphore for shorter times etc and to handle VM_FAULT_RETRY and other
"newer" things, so it would be a good idea to bring all those
improvements to the generic case and teach other architectures about
them too.
Reported-and-tested-by: NTakashi Iwai <tiwai@suse.de>
Tested-by: NJan Engelhardt <jengelh@inai.de>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com> # "s390 still compiles and boots"
Cc: linux-arch@vger.kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      33692f27
  9. 29 1月, 2015 1 次提交
  11. 28 1月, 2015 4 次提交
  13. 27 1月, 2015 1 次提交
  15. 24 1月, 2015 1 次提交
  17. 23 1月, 2015 12 次提交
  19. 22 1月, 2015 13 次提交