Re: [PATCH v11 09/35] KVM: x86: Determine shared/private faults based on vm_type

Paolo Bonzini
2024-02-12T10:31:41Z

On Sat, Dec 30, 2023 at 6:24 PM Michael Roth <michael.roth@amd.com> wrote:
>
> For KVM_X86_SNP_VM, only the PFERR_GUEST_ENC_MASK flag is needed to
> determine with an #NPF is due to a private/shared access by the guest.
> Implement that handling here. Also add handling needed to deal with
> SNP guests which in some cases will make MMIO accesses with the
> encryption bit.
>
> Signed-off-by: Michael Roth <michael.roth@amd.com>
> ---
> arch/x86/kvm/mmu/mmu.c | 12 ++++++++++--
> arch/x86/kvm/mmu/mmu_internal.h | 20 +++++++++++++++++++-
> 2 files changed, 29 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index d3fbfe0686a0..61213f6648a1 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4331,6 +4331,7 @@ static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
> static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> {
> struct kvm_memory_slot *slot = fault->slot;
> + bool private_fault = fault->is_private;

I think it's nicer to just make the fault !is_private in
kvm_mmu_do_page_fault().

> +static bool kvm_mmu_fault_is_private(struct kvm *kvm, gpa_t gpa, u64 err)
> +{
> + bool private_fault = false;
> +
> + if (kvm_is_vm_type(kvm, KVM_X86_SNP_VM)) {
> + private_fault = !!(err & PFERR_GUEST_ENC_MASK);
> + } else if (kvm_is_vm_type(kvm, KVM_X86_SW_PROTECTED_VM)) {
> + /*
> + * This handling is for gmem self-tests and guests that treat
> + * userspace as the authority on whether a fault should be
> + * private or not.
> + */
> + private_fault = kvm_mem_is_private(kvm, gpa >> PAGE_SHIFT);
> + }

Any reason to remove the is_private page fault that was there in
previous versions of the patch? I don't really like having both TDX
and SVM-specific code in this function.

Paolo

> + return private_fault;
> +}
> +
> /*
> * Return values of handle_mmio_page_fault(), mmu.page_fault(), fast_page_fault(),
> * and of course kvm_mmu_do_page_fault().
> @@ -298,7 +316,7 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> .max_level = KVM_MAX_HUGEPAGE_LEVEL,
> .req_level = PG_LEVEL_4K,
> .goal_level = PG_LEVEL_4K,
> - .is_private = kvm_mem_is_private(vcpu->kvm, cr2_or_gpa >> PAGE_SHIFT),
> + .is_private = kvm_mmu_fault_is_private(vcpu->kvm, cr2_or_gpa, err),
> };
> int r;
>
> --
> 2.25.1
>