Re: [PATCH v2 1/6] KVM: x86/mmu: Fix wrong gfn range of tlb flushing in validate_direct_spte()

[David Matlack]

On Thu, Sep 15, 2022 at 4:47 AM Liam Ni <zhiguangni01@xxxxxxxxx> wrote:
>
> On Tue, 13 Sept 2022 at 20:13, Hou Wenlong <houwenlong.hwl@xxxxxxxxxxxx> wrote:
> >
> > On Thu, Sep 08, 2022 at 01:43:54AM +0800, David Matlack wrote:
> > > On Wed, Aug 24, 2022 at 05:29:18PM +0800, Hou Wenlong wrote:
> > > > The spte pointing to the children SP is dropped, so the
> > > > whole gfn range covered by the children SP should be flushed.
> > > > Although, Hyper-V may treat a 1-page flush the same if the
> > > > address points to a huge page, it still would be better
> > > > to use the correct size of huge page. Also introduce
> > > > a helper function to do range-based flushing when a direct
> > > > SP is dropped, which would help prevent future buggy use
> > > > of kvm_flush_remote_tlbs_with_address() in such case.
> > > >
> > > > Fixes: c3134ce240eed ("KVM: Replace old tlb flush function with new one to flush a specified range.")
> > > > Suggested-by: David Matlack <dmatlack@xxxxxxxxxx>
> > > > Signed-off-by: Hou Wenlong <houwenlong.hwl@xxxxxxxxxxxx>
> > > > ---
> > > >  arch/x86/kvm/mmu/mmu.c | 10 +++++++++-
> > > >  1 file changed, 9 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > > > index e418ef3ecfcb..a3578abd8bbc 100644
> > > > --- a/arch/x86/kvm/mmu/mmu.c
> > > > +++ b/arch/x86/kvm/mmu/mmu.c
> > > > @@ -260,6 +260,14 @@ void kvm_flush_remote_tlbs_with_address(struct kvm *kvm,
> > > >     kvm_flush_remote_tlbs_with_range(kvm, &range);
> > > >  }
> > > >
> > > > +/* Flush all memory mapped by the given direct SP. */
> > > > +static void kvm_flush_remote_tlbs_direct_sp(struct kvm *kvm, struct kvm_mmu_page *sp)
> > > > +{
> > > > +   WARN_ON_ONCE(!sp->role.direct);
> > > > +   kvm_flush_remote_tlbs_with_address(kvm, sp->gfn,
> > > > +                                      KVM_PAGES_PER_HPAGE(sp->role.level + 1));
>
> Do we need "+1" here?    sp->role.level=1 means 4k page.
> I think here should be   “KVM_PAGES_PER_HPAGE(sp->role.level)”

Yes we need the "+ 1" here. kvm_flush_remote_tlbs_direct_sp() must
flush all memory mapped by the shadow page, which is equivalent to the
amount of memory mapped by a huge page at the next higher level. For
example, a shadow page with role.level == PG_LEVEL_4K maps 2 MiB of
the guest physical address space since 512 PTEs x 4KiB per PTE = 2MiB.

>
> > >
> > > nit: I think it would make sense to introduce
> > > kvm_flush_remote_tlbs_gfn() in this patch since you are going to
> > > eventually use it here anyway.
> > >
> > OK, I'll do it in the next version. Thanks!
> >
> > > > +}
> > > > +
> > > >  static void mark_mmio_spte(struct kvm_vcpu *vcpu, u64 *sptep, u64 gfn,
> > > >                        unsigned int access)
> > > >  {
> > > > @@ -2341,7 +2349,7 @@ static void validate_direct_spte(struct kvm_vcpu *vcpu, u64 *sptep,
> > > >                     return;
> > > >
> > > >             drop_parent_pte(child, sptep);
> > > > -           kvm_flush_remote_tlbs_with_address(vcpu->kvm, child->gfn, 1);
> > > > +           kvm_flush_remote_tlbs_direct_sp(vcpu->kvm, child);
> > > >     }
> > > >  }
> > > >
> > > > --
> > > > 2.31.1
> > > >