Messages in this thread | ![/](/images/icornerl.gif) | | Date | Sat, 30 Mar 2024 22:35:17 +0100 | Subject | Re: [PATCH v12 23/29] KVM: x86: Implement gmem hook for determining max NPT mapping level | From | Paolo Bonzini <> |
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On 3/29/24 23:58, Michael Roth wrote: > In the case of SEV-SNP, whether or not a 2MB page can be mapped via a > 2MB mapping in the guest's nested page table depends on whether or not > any subpages within the range have already been initialized as private > in the RMP table. The existing mixed-attribute tracking in KVM is > insufficient here, for instance: > > - gmem allocates 2MB page > - guest issues PVALIDATE on 2MB page > - guest later converts a subpage to shared > - SNP host code issues PSMASH to split 2MB RMP mapping to 4K > - KVM MMU splits NPT mapping to 4K > - guest later converts that shared page back to private > > At this point there are no mixed attributes, and KVM would normally > allow for 2MB NPT mappings again, but this is actually not allowed > because the RMP table mappings are 4K and cannot be promoted on the > hypervisor side, so the NPT mappings must still be limited to 4K to > match this. > > Implement a kvm_x86_ops.gmem_validate_fault() hook for SEV that checks > for this condition and adjusts the mapping level accordingly. > > Signed-off-by: Michael Roth <michael.roth@amd.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> --- > arch/x86/kvm/svm/sev.c | 32 ++++++++++++++++++++++++++++++++ > arch/x86/kvm/svm/svm.c | 1 + > arch/x86/kvm/svm/svm.h | 7 +++++++ > 3 files changed, 40 insertions(+) > > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c > index 87d621d013a4..31f6f4786503 100644 > --- a/arch/x86/kvm/svm/sev.c > +++ b/arch/x86/kvm/svm/sev.c > @@ -4443,3 +4443,35 @@ void sev_gmem_invalidate(kvm_pfn_t start, kvm_pfn_t end) > pfn += use_2m_update ? PTRS_PER_PMD : 1; > } > } > + > +/* > + * Re-check whether an #NPF for a private/gmem page can still be serviced, and > + * adjust maximum mapping level if needed. > + */ > +int sev_gmem_validate_fault(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, bool is_private, > + u8 *max_level) > +{ > + int level, rc; > + bool assigned; > + > + if (!sev_snp_guest(kvm)) > + return 0; > + > + rc = snp_lookup_rmpentry(pfn, &assigned, &level); > + if (rc) { > + pr_err_ratelimited("SEV: RMP entry not found: GFN %llx PFN %llx level %d error %d\n", > + gfn, pfn, level, rc); > + return -ENOENT; > + } > + > + if (!assigned) { > + pr_err_ratelimited("SEV: RMP entry is not assigned: GFN %llx PFN %llx level %d\n", > + gfn, pfn, level); > + return -EINVAL; > + } > + > + if (level < *max_level) > + *max_level = level; > + > + return 0; > +} > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > index b456906f2670..298b4ce77a5f 100644 > --- a/arch/x86/kvm/svm/svm.c > +++ b/arch/x86/kvm/svm/svm.c > @@ -5081,6 +5081,7 @@ static struct kvm_x86_ops svm_x86_ops __initdata = { > > .gmem_prepare = sev_gmem_prepare, > .gmem_invalidate = sev_gmem_invalidate, > + .gmem_validate_fault = sev_gmem_validate_fault, > }; > > /* > diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h > index 3f1f6d3d3ade..746f819a6de4 100644 > --- a/arch/x86/kvm/svm/svm.h > +++ b/arch/x86/kvm/svm/svm.h > @@ -732,6 +732,8 @@ void sev_vcpu_unblocking(struct kvm_vcpu *vcpu); > void sev_snp_init_protected_guest_state(struct kvm_vcpu *vcpu); > int sev_gmem_prepare(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, int max_order); > void sev_gmem_invalidate(kvm_pfn_t start, kvm_pfn_t end); > +int sev_gmem_validate_fault(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, bool is_private, > + u8 *max_level); > #else > static inline struct page *snp_safe_alloc_page(struct kvm_vcpu *vcpu) { > return alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO); > @@ -753,6 +755,11 @@ static inline int sev_gmem_prepare(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, in > return 0; > } > static inline void sev_gmem_invalidate(kvm_pfn_t start, kvm_pfn_t end) {} > +static inline int sev_gmem_validate_fault(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, > + bool is_private, u8 *max_level) > +{ > + return 0; > +} > > #endif >
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