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 <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Huang Rui <[email protected]>
Cc: John Stultz <[email protected]>
Cc: Len Brown <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Marcelo Tosatti <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Radim Krcmar <[email protected]>
Cc: Ralf Baechle <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: kvm ML <[email protected]>
Link: http://lkml.kernel.org/r/678981cc4761fb38a793c217c9cac42503cf3719.1434501121.git.luto@kernel.org
[ Ported it to v4.2-rc1. ]
Signed-off-by: Ingo Molnar <[email protected]>

diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
index 5c490db62e32133c69b3cb8f87fe08e4a91b7cbc..7a6bed5c08bc3cc266dcc7c24e71863f684d2630 100644 (file)
--- 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;