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

Robert Hoo
2022-09-18T13:11:12Z

On Wed, 2022-08-24 at 17:29 +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@google.com>
> Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
> ---
> 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);

What if !sp->role.direct? Below flushing sp->gfn isn't expected? but
still to do it. Is this operation harmless?

> + kvm_flush_remote_tlbs_with_address(kvm, sp->gfn,
> + KVM_PAGES_PER_HPAGE(sp-
> >role.level + 1));
> +}
> +
> 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);
> }
> }
>