Re: [PATCH] mmu_notifier, kvm: Introduce dirty bit tracking in spte and mmu notifier to help KSM dirty bit tracking

[Avi Kivity <avi@redhat.com>]

On 06/22/2011 02:05 PM, Izik Eidus wrote:
>>> +    spte = rmap_next(kvm, rmapp, NULL);
>>> +    while (spte) {
>>> +        int _dirty;
>>> +        u64 _spte = *spte;
>>> +        BUG_ON(!(_spte&  PT_PRESENT_MASK));
>>> +        _dirty = _spte&  PT_DIRTY_MASK;
>>> +        if (_dirty) {
>>> +            dirty = 1;
>>> +            clear_bit(PT_DIRTY_SHIFT, (unsigned long *)spte);
>>> +        }
>>
>> Racy.  Also, needs a tlb flush eventually.
> +
>
> Hi, one of the issues is that the whole point of this patch is not do 
> tlb flush eventually,
> But I see your point, because other users will not expect such 
> behavior, so maybe there is need into a parameter
> flush_tlb=?, or add another mmu notifier call?
>

If you don't flush the tlb, a subsequent write will not see that spte.d 
is clear and the write will happen.  So you'll see the page as clean 
even though it's dirty.  That's not acceptable.

-- 
error compiling committee.c: too many arguments to function

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