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author | Ingo Molnar <mingo@elte.hu> | 2009-06-16 08:23:32 (GMT) |
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committer | Ingo Molnar <mingo@elte.hu> | 2009-06-16 08:23:32 (GMT) |
commit | 5dfaf90f8052327c92fbe3c470a2e6634be296c0 (patch) | |
tree | d29c1191df48fcf1180a8509f93744d343e58d17 /arch/x86/mm/fault.c | |
parent | 507fa3a3d80365c595113a5ac3232309e3dbf5d8 (diff) | |
download | linux-fsl-qoriq-5dfaf90f8052327c92fbe3c470a2e6634be296c0.tar.xz |
x86: mm: Read cr2 before prefetching the mmap_lock
Prefetch instructions can generate spurious faults on certain
models of older CPUs. The faults themselves cannot be stopped
and they can occur pretty much anywhere - so the way we solve
them is that we detect certain patterns and ignore the fault.
There is one small path of code where we must not take faults
though: the #PF handler execution leading up to the reading
of the CR2 (the faulting address). If we take a fault there
then we destroy the CR2 value (with that of the prefetching
instruction's) and possibly mishandle user-space or
kernel-space pagefaults.
It turns out that in current upstream we do exactly that:
prefetchw(&mm->mmap_sem);
/* Get the faulting address: */
address = read_cr2();
This is not good.
So turn around the order: first read the cr2 then prefetch
the lock address. Reading cr2 is plenty fast (2 cycles) so
delaying the prefetch by this amount shouldnt be a big issue
performance-wise.
[ And this might explain a mystery fault.c warning that sometimes
occurs on one an old AMD/Semptron based test-system i have -
which does have such prefetch problems. ]
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Vegard Nossum <vegard.nossum@gmail.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
LKML-Reference: <20090616030522.GA22162@Krystal>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch/x86/mm/fault.c')
-rw-r--r-- | arch/x86/mm/fault.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index c6acc63..0482fa6 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -951,11 +951,11 @@ do_page_fault(struct pt_regs *regs, unsigned long error_code) tsk = current; mm = tsk->mm; - prefetchw(&mm->mmap_sem); - /* Get the faulting address: */ address = read_cr2(); + prefetchw(&mm->mmap_sem); + if (unlikely(kmmio_fault(regs, address))) return; |