On Fri, Jan 04, 2019 at 07:50:36AM -0800, Sean Christopherson wrote:
> On Fri, Jan 04, 2019 at 04:54:01PM +0800, lantianyu1986@xxxxxxxxx wrote:
> > From: Lan Tianyu <Tianyu.Lan@xxxxxxxxxxxxx>
> >
> > The dirty bits have already been checked in the previous check of
> > "dirty_bitmap" and mask must be non-zero value at this point.
> >
> > Signed-off-by: Lan Tianyu <Tianyu.Lan@xxxxxxxxxxxxx>
> > ---
> > virt/kvm/kvm_main.c | 8 +++-----
> > 1 file changed, 3 insertions(+), 5 deletions(-)
> >
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index cf7cc0554094..e75dbb15fd09 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -1206,11 +1206,9 @@ int kvm_get_dirty_log_protect(struct kvm *kvm,
> > mask = xchg(&dirty_bitmap[i], 0);
> > dirty_bitmap_buffer[i] = mask;
> >
> > - if (mask) {
> > - offset = i * BITS_PER_LONG;
> > - kvm_arch_mmu_enable_log_dirty_pt_masked(kvm, memslot,
> > - offset, mask);
> > - }
> > + offset = i * BITS_PER_LONG;
> > + kvm_arch_mmu_enable_log_dirty_pt_masked(kvm, memslot,
> > + offset, mask);
>
> Hmm, the check against mask was explicitly added by commit 58d2930f4ee3
> ("KVM: Eliminate extra function calls in kvm_get_dirty_log_protect()").
> AFAIK KVM only *sets* bits in dirty_bitmap without holding slots_lock
> and/or mmu_lock, so I agree that checking mask is redundant, but it'd be
> nice to elaborate a bit more in the changelog.
>
> At the very least this needs a Fixes tag for the aforementioned commit.
Actually, this can be a straight revert of 58d2930f4ee3.
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