Re: [PATCH v4 2/6] KVM: x86/mmu: Fix wrong gfn range of tlb flushing in kvm_set_pte_rmapp()

[Lai Jiangshan]

On Thu, Oct 13, 2022 at 1:00 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> On Mon, Oct 10, 2022, Hou Wenlong wrote:
> > When the spte of hupe page is dropped in kvm_set_pte_rmapp(), the whole
> > gfn range covered by the spte should be flushed. However,
> > rmap_walk_init_level() doesn't align down the gfn for new level like tdp
> > iterator does, then the gfn used in kvm_set_pte_rmapp() is not the base
> > gfn of huge page. And the size of gfn range is wrong too for huge page.
> > Use the base gfn of huge page and the size of huge page for flushing
> > tlbs for huge page. Also introduce a helper function to flush the given
> > page (huge or not) of guest memory, 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.")
> > Signed-off-by: Hou Wenlong <houwenlong.hwl@xxxxxxxxxxxx>
> > ---
> >  arch/x86/kvm/mmu/mmu.c          |  4 +++-
> >  arch/x86/kvm/mmu/mmu_internal.h | 10 ++++++++++
> >  2 files changed, 13 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index 7de3579d5a27..4874c603ed1c 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -1430,7 +1430,9 @@ static bool kvm_set_pte_rmap(struct kvm *kvm, struct kvm_rmap_head *rmap_head,
> >       }
> >
> >       if (need_flush && kvm_available_flush_tlb_with_range()) {
> > -             kvm_flush_remote_tlbs_with_address(kvm, gfn, 1);
> > +             gfn_t base = gfn_round_for_level(gfn, level);
> > +
> > +             kvm_flush_remote_tlbs_gfn(kvm, base, level);
> >               return false;
> >       }
> >
> > diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
> > index 17488d70f7da..249bfcd502b4 100644
> > --- a/arch/x86/kvm/mmu/mmu_internal.h
> > +++ b/arch/x86/kvm/mmu/mmu_internal.h
> > @@ -168,8 +168,18 @@ void kvm_mmu_gfn_allow_lpage(const struct kvm_memory_slot *slot, gfn_t gfn);
> >  bool kvm_mmu_slot_gfn_write_protect(struct kvm *kvm,
> >                                   struct kvm_memory_slot *slot, u64 gfn,
> >                                   int min_level);
> > +
> >  void kvm_flush_remote_tlbs_with_address(struct kvm *kvm,
> >                                       u64 start_gfn, u64 pages);
> > +
> > +/* Flush the given page (huge or not) of guest memory. */
> > +static inline void kvm_flush_remote_tlbs_gfn(struct kvm *kvm, gfn_t gfn, int level)
> > +{
> > +     u64 pages = KVM_PAGES_PER_HPAGE(level);
> > +
>
> Rather than require the caller to align gfn, what about doing gfn_round_for_level()
> in this helper?  It's a little odd that the caller needs to align gfn but doesn't
> have to compute the size.
>
> I'm 99% certain kvm_set_pte_rmap() is the only path that doesn't already align the
> gfn, but it's nice to not have to worry about getting this right, e.g. alternatively
> this helper could WARN if the gfn is misaligned, but that's _more work.
>
>         kvm_flush_remote_tlbs_with_address(kvm, gfn_round_for_level(gfn, level),
>                                            KVM_PAGES_PER_HPAGE(level);
>
> If no one objects, this can be done when the series is applied, i.e. no need to
> send v5 just for this.
>

Hello Paolo, Sean, Hou,

It seems the patchset has not been queued.  I believe it does
fix bugs.

Thanks
Lai