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Date: Sat, 17 Apr 2010 21:49:53 +0300
From: Avi Kivity <avi@redhat.com>
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To: Glauber Costa <glommer@redhat.com>
CC: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
       Jeremy Fitzhardinge <jeremy@goop.org>,
       Marcelo Tosatti <mtosatti@redhat.com>,
       Zachary Amsden <zamsden@redhat.com>
Subject: Re: [PATCH 1/5] Add a global synchronization point for pvclock
References: <1271356648-5108-1-git-send-email-glommer@redhat.com> <1271356648-5108-2-git-send-email-glommer@redhat.com> <4BCA026D.3070309@redhat.com>
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On 04/17/2010 09:48 PM, Avi Kivity wrote:
>
>>
>> +static u64 last_value = 0;
>
> Needs to be atomic64_t.
>
>> +
>>   cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
>>   {
>>       struct pvclock_shadow_time shadow;
>>       unsigned version;
>>       cycle_t ret, offset;
>> +    u64 last;
>>
>>
>> +    do {
>> +        last = last_value;
>
> Otherwise, this assignment can see a partial update.

On a 32-bit guest, that is.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.