Re: [PATCH 9/9] KVM: x86/mmu: Try to handle no-slot faults during kvm_faultin_pfn()

[David Matlack <dmatlack@google.com>]

On Mon, Aug 15, 2022 at 4:01 PM David Matlack <dmatlack@google.com> wrote:
>
> Try to handle faults on GFNs that do not have a backing memslot during
> kvm_faultin_pfn(), rather than relying on the caller to call
> handle_abnormal_pfn() right after kvm_faultin_pfn(). This reduces all of
> the page fault paths by eliminating duplicate code.
>
> Opportunistically tweak the comment about handling gfn > host.MAXPHYADDR
> to reflect that the effect of returning RET_PF_EMULATE at that point is
> to avoid creating an MMIO SPTE for such GFNs.
>
> No functional change intended.
>
> Signed-off-by: David Matlack <dmatlack@google.com>
> ---
>  arch/x86/kvm/mmu/mmu.c         | 55 +++++++++++++++++-----------------
>  arch/x86/kvm/mmu/paging_tmpl.h |  4 ---
>  2 files changed, 27 insertions(+), 32 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
[...]
> @@ -4181,6 +4185,9 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
>         if (unlikely(is_error_pfn(fault->pfn)))
>                 return kvm_handle_error_pfn(fault);
>
> +       if (unlikely(!fault->slot))
> +               return kvm_handle_noslot_fault(vcpu, fault, ACC_ALL);

This is broken. This needs to be pte_access for the shadow paging
case, not ACC_ALL. I remember now I had that in an earlier version but
it got lost at some point when I was rebasing locally.