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SubjectRe: [PATCH 3/3] KVM: x86: fix use of L1 MMIO areas in nested guests
2017-08-18 09:59+0200, David Hildenbrand:
> On 17.08.2017 18:36, Paolo Bonzini wrote:
> > There is currently some confusion between nested and L1 GPAs. The
> > assignment to "direct" in kvm_mmu_page_fault tries to fix that, but
> > it is not enough. What this patch does is fence off the MMIO cache
> > completely when using shadow nested page tables, since we have neither
> > a GVA nor an L1 GPA to put in the cache. This also allows some
> > simplifications in kvm_mmu_page_fault and FNAME(page_fault).
> >
> > The EPT misconfig likewise does not have an L1 GPA to pass to
> > kvm_io_bus_write, so that must be skipped for guest mode.
> >
> > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> > ---
> > v1->v2: standardize on "nGPA" moniker, replace nested ifs with &&
> >
> > arch/x86/kvm/mmu.c | 10 +++++++++-
> > arch/x86/kvm/paging_tmpl.h | 3 +--
> > arch/x86/kvm/vmx.c | 7 ++++++-
> > arch/x86/kvm/x86.h | 6 +++++-
> > 4 files changed, 21 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> > index a2c592b14617..02f8c507b160 100644
> > --- a/arch/x86/kvm/mmu.c
> > +++ b/arch/x86/kvm/mmu.c
> > @@ -3596,6 +3596,14 @@ static bool is_shadow_zero_bits_set(struct kvm_mmu *mmu, u64 spte, int level)
> >
> > static bool mmio_info_in_cache(struct kvm_vcpu *vcpu, u64 addr, bool direct)
> > {
> > + /*
> > + * A nested guest cannot use the MMIO cache if it is using nested
> > + * page tables, because cr2 is a nGPA while the cache stores L1's
> > + * physical addresses.
>
> ... "while the cache stores GPAs" ?

Makes sense, changed while applying.

> > diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> > @@ -90,7 +90,11 @@ static inline u32 bit(int bitno)
> > static inline void vcpu_cache_mmio_info(struct kvm_vcpu *vcpu,
> > gva_t gva, gfn_t gfn, unsigned access)
> > {
> > - vcpu->arch.mmio_gva = gva & PAGE_MASK;
> > + /*
> > + * If this is a shadow nested page table, the "GVA" is
>
> s/"GVA"/GVA/ ?

I prefer the former, we're talking about "gva_t gva" that isn't GVA. :)

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