On 09/06/2016 14:43, Roman Kagan wrote:
> On Thu, Jun 09, 2016 at 01:23:23PM +0200, Paolo Bonzini wrote:
>> The version field in struct pvclock_vcpu_time_info basically implements
>> a seqcount. Wrap it with the usual read_begin and read_retry functions,
>> and use these APIs instead of peppering the code with smp_rmb()s.
>> While at it, change it to the more pedantically correct virt_rmb().
>>
>> With this change, __pvclock_read_cycles can be simplified noticeably.
>>
>> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>> ---
>> arch/x86/entry/vdso/vclock_gettime.c | 25 +++++------------------
>> arch/x86/include/asm/pvclock.h | 39 +++++++++++++++++++++---------------
>> arch/x86/kernel/pvclock.c | 17 ++++++----------
>> 3 files changed, 34 insertions(+), 47 deletions(-)
> [...]
>> --- a/arch/x86/include/asm/pvclock.h
>> +++ b/arch/x86/include/asm/pvclock.h
> [...]
>> @@ -69,23 +87,12 @@ static inline u64 pvclock_scale_delta(u64 delta, u32 mul_frac, int shift)
>> }
>>
>> static __always_inline
>> -unsigned __pvclock_read_cycles(const struct pvclock_vcpu_time_info *src,
>> - cycle_t *cycles, u8 *flags)
>> +cycle_t __pvclock_read_cycles(const struct pvclock_vcpu_time_info *src)
>> {
>> - unsigned version;
>> - cycle_t offset;
>> - u64 delta;
>> -
>> - version = src->version;
>> - /* Make the latest version visible */
>> - smp_rmb();
>
> This is on top of Minfei's patch, right? It isn't in Linus' tree yet so
> I wonder if it makes sense to merge the two patches into one.
>
> Will you post it to stable, too?
Not this one, because Minfei's patch is enough to fix the bug, but I do
plan on including it in 4.7 to simplify the merging (kvm/next has
already been branched off Linus's tree).
Paolo
> Anyway
>
> Reviewed-by: Roman Kagan <rkagan@xxxxxxxxxxxxx>
>
> Roman.
>
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