lkml.org 
[lkml]   [2015]   [Jun]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 17/19] x86/kvm/tsc: Drop extra barrier and use rdtsc_ordered() in kvmclock
Date
From: Andy Lutomirski <luto@kernel.org>

__pvclock_read_cycles() had an unnecessary barrier. Get rid of that
barrier and clean up the code by just using rdtsc_ordered().

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Huang Rui <ray.huang@amd.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: kvm ML <kvm@vger.kernel.org>
Cc: Len Brown <lenb@kernel.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Radim Krcmar <rkrcmar@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: x86-ml <x86@kernel.org>
Link: http://lkml.kernel.org/r/678981cc4761fb38a793c217c9cac42503cf3719.1434501121.git.luto@kernel.org
Signed-off-by: Borislav Petkov <bp@suse.de>
---
arch/x86/include/asm/pvclock.h | 10 +---------
1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
index 6084bce345fc..b6c9c9eda914 100644
--- a/arch/x86/include/asm/pvclock.h
+++ b/arch/x86/include/asm/pvclock.h
@@ -62,7 +62,7 @@ static inline u64 pvclock_scale_delta(u64 delta, u32 mul_frac, int shift)
static __always_inline
u64 pvclock_get_nsec_offset(const struct pvclock_vcpu_time_info *src)
{
- u64 delta = rdtsc() - src->tsc_timestamp;
+ u64 delta = rdtsc_ordered() - src->tsc_timestamp;
return pvclock_scale_delta(delta, src->tsc_to_system_mul,
src->tsc_shift);
}
@@ -76,17 +76,9 @@ unsigned __pvclock_read_cycles(const struct pvclock_vcpu_time_info *src,
u8 ret_flags;

version = src->version;
- /* Note: emulated platforms which do not advertise SSE2 support
- * result in kvmclock not using the necessary RDTSC barriers.
- * Without barriers, it is possible that RDTSC instruction reads from
- * the time stamp counter outside rdtsc_barrier protected section
- * below, resulting in violation of monotonicity.
- */
- rdtsc_barrier();
offset = pvclock_get_nsec_offset(src);
ret = src->system_time + offset;
ret_flags = src->flags;
- rdtsc_barrier();

*cycles = ret;
*flags = ret_flags;
--
2.3.5


\
 
 \ /
  Last update: 2015-06-25 19:01    [W:0.202 / U:24.020 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site