Re: [PATCH] kvm: arm: Fix handling of stage2 huge mappings

[Suzuki K Poulose]

Marc,

On 20/03/2019 10:11, Marc Zyngier wrote:
> On Wed, 20 Mar 2019 09:44:38 +0000
> Suzuki K Poulose <suzuki.poulose@xxxxxxx> wrote:
>
> > Hi Marc,
> >
> > On 20/03/2019 08:15, Marc Zyngier wrote:
> > > Hi Suzuki,
> > >
> > > On Tue, 19 Mar 2019 14:11:08 +0000,
> > > Suzuki K Poulose <suzuki.poulose@xxxxxxx> wrote:
> > > > We rely on the mmu_notifier call backs to handle the split/merge
> > > > of huge pages and thus we are guaranteed that, while creating a
> > > > block mapping, either the entire block is unmapped at stage2 or it
> > > > is missing permission.
> > > >
> > > > However, we miss a case where the block mapping is split for dirty
> > > > logging case and then could later be made block mapping, if we cancel the
> > > > dirty logging. This not only creates inconsistent TLB entries for
> > > > the pages in the the block, but also leakes the table pages for
> > > > PMD level.
> > > >
> > > > Handle this corner case for the huge mappings at stage2 by
> > > > unmapping the non-huge mapping for the block. This could potentially
> > > > release the upper level table. So we need to restart the table walk
> > > > once we unmap the range.
> > > >
> > > > Fixes : ad361f093c1e31d ("KVM: ARM: Support hugetlbfs backed huge pages")
> > > > Reported-by: Zheng Xiang <zhengxiang9@xxxxxxxxxx>
> > > > Cc: Zheng Xiang <zhengxiang9@xxxxxxxxxx>
> > > > Cc: Zhengui Yu <yuzenghui@xxxxxxxxxx>
> > > > Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
> > > > Cc: Christoffer Dall <christoffer.dall@xxxxxxx>
> > > > Signed-off-by: Suzuki K Poulose ...


> > > > +		if (!pmd_thp_or_huge(old_pmd)) {
> > > > +			unmap_stage2_range(kvm, addr & S2_PMD_MASK, S2_PMD_SIZE);
> > > > +			goto retry;

> > > > +		if (!stage2_pud_huge(kvm, old_pud)) {
> > > > +			unmap_stage2_range(kvm, addr & S2_PUD_MASK, S2_PUD_SIZE);

> > We should really get rid of the S2_P{U/M}D_* definitions, as they are
> > always the same as the host. The only thing that changes is the PGD size
> > which varies according to the IPA and the concatenation.

Also what do you think about using  P{M,U}D_* instead of S2_P{M,U}D_*
above ? I could make that change with the respin.

> Sure, feel free to send a fixed version. I'll drop the currently queued
> patch.


Thanks. Sorry for the trouble.

Cheers
Suzuki