Re: [PATCH 3/4] KVM: Count the number of dirty pages for dirty logging

[Avi Kivity <avi@redhat.com>]

On 11/14/2011 12:07 PM, Avi Kivity wrote:
> On 11/14/2011 11:23 AM, Takuya Yoshikawa wrote:
> > Needed for the next patch which uses this number to decide how to write
> > protect a slot.
> >
> >  	/* If nothing is dirty, don't bother messing with page tables. */
> > -	if (is_dirty) {
> > +	if (memslot->nr_dirty_pages) {
> >  		struct kvm_memslots *slots, *old_slots;
> >  		unsigned long *dirty_bitmap;
> >  
> > @@ -3504,6 +3500,7 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
> >  			goto out;
> >  		memcpy(slots, kvm->memslots, sizeof(struct kvm_memslots));
> >  		slots->memslots[log->slot].dirty_bitmap = dirty_bitmap;
> > +		slots->memslots[log->slot].nr_dirty_pages = 0;
> >  		slots->generation++;
> >  
> >  #endif /* !CONFIG_S390 */
> > @@ -1491,7 +1492,8 @@ void mark_page_dirty_in_slot(struct kvm *kvm, struct kvm_memory_slot *memslot,
> >  	if (memslot && memslot->dirty_bitmap) {
> >  		unsigned long rel_gfn = gfn - memslot->base_gfn;
> >  
> > -		__set_bit_le(rel_gfn, memslot->dirty_bitmap);
> > +		if (!__test_and_set_bit_le(rel_gfn, memslot->dirty_bitmap))
> > +			memslot->nr_dirty_pages++;
> >  	}
> >  }
> >  
>
> The two assignments to ->nr_dirty_pages can race, no?  Nothing protects it.
>

er, it can't, it's before the rcu_assign_pointer().

-- 
error compiling committee.c: too many argumen
ts to function