On 09/06/2016 15:35, Roman Kagan wrote:
> On Thu, Jun 09, 2016 at 02:47:54PM +0200, Paolo Bonzini wrote:
>> 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
>
> Has it landed in any public tree? I'm unable to find any. There
> appears to be another version of the patch on the list, so I'm confused.
I'm about to push it to kvm/master.
Paolo
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