On Wed, Jun 23, 2021, Paolo Bonzini wrote: > On 22/06/21 19:57, Sean Christopherson wrote: > > Drop the smep_andnot_wp role check from the "uses NX" calculation now > > that all non-nested shadow MMUs treat NX as used via the !TDP check. > > > > The shadow MMU for nested NPT, which shares the helper, does not need to > > deal with SMEP (or WP) as NPT walks are always "user" accesses and WP is > > explicitly noted as being ignored: > > > > Table walks for guest page tables are always treated as user writes at > > the nested page table level. > > > > A table walk for the guest page itself is always treated as a user > > access at the nested page table level > > > > The host hCR0.WP bit is ignored under nested paging. > > > > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> > > --- > > arch/x86/kvm/mmu/mmu.c | 3 +-- > > 1 file changed, 1 insertion(+), 2 deletions(-) > > > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > > index 96c16a6e0044..ca7680d1ea24 100644 > > --- a/arch/x86/kvm/mmu/mmu.c > > +++ b/arch/x86/kvm/mmu/mmu.c > > @@ -4223,8 +4223,7 @@ reset_shadow_zero_bits_mask(struct kvm_vcpu *vcpu, struct kvm_mmu *context) > > * NX can be used by any non-nested shadow MMU to avoid having to reset > > * MMU contexts. Note, KVM forces EFER.NX=1 when TDP is disabled. > > */ > > - bool uses_nx = context->nx || !tdp_enabled || > > - context->mmu_role.base.smep_andnot_wp; > > + bool uses_nx = context->nx || !tdp_enabled; > > struct rsvd_bits_validate *shadow_zero_check; > > int i; > > > > Good idea, but why not squash it into patch 2? Because that patch is marked for stable and dropping the smep_andnot_wp is not necessary to fix the bug. At worst, the too-liberal uses_nx will suppress the WARN in handle_mmio_page_fault() because this is for checking KVM's SPTEs, not the guest's SPTEs, i.e. KVM won't miss a guest reserved NX #PF. That said, I'm not at all opposed to squashing this. I have a feeling I originally split the patches because I wasn't super confident about either change, and never revisited them.
