[tip:x86/asm] x86/asm/tsc, x86/kvm: Drop open-coded barrier and use rdtsc_ordered() in kvmclock

[tip-bot for Andy Lutomirski]

Commit-ID:  502dfeff239e8313bfbe906ca0a1a6827ac8481b
Gitweb:     http://git.kernel.org/tip/502dfeff239e8313bfbe906ca0a1a6827ac8481b
Author:     Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Thu, 25 Jun 2015 18:44:11 +0200
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Mon, 6 Jul 2015 15:23:30 +0200

x86/asm/tsc, x86/kvm: Drop open-coded barrier and use rdtsc_ordered() in kvmclock

__pvclock_read_cycles() used to have two barriers, one of which was unnecessary,
which got removed after an initial version of this patch was sent.

But the barrier is still open-coded unnecessarily - get rid of
that barrier and clean up the code by just using rdtsc_ordered().

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Huang Rui <ray.huang@xxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Cc: Len Brown <lenb@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Radim Krcmar <rkrcmar@xxxxxxxxxx>
Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: kvm ML <kvm@xxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/678981cc4761fb38a793c217c9cac42503cf3719.1434501121.git.luto@xxxxxxxxxx
[ Ported it to v4.2-rc1. ]
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/include/asm/pvclock.h | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
index 5c490db..7a6bed5 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);
 }
@@ -76,13 +76,7 @@ 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;
--
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