From 44f42ef37deb49682abf0108bf9ede88d4478a20 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Tue, 27 Feb 2024 18:41:40 -0800 Subject: [PATCH] KVM: x86/mmu: Move private vs. shared check above slot validity checks Prioritize private vs. shared gfn attribute checks above slot validity checks to ensure a consistent userspace ABI. E.g. as is, KVM will exit to userspace if there is no memslot, but emulate accesses to the APIC access page even if the attributes mismatch. Fixes: 8dd2eee9d526 ("KVM: x86/mmu: Handle page fault for private memory") Cc: Yu Zhang Cc: Chao Peng Cc: Fuad Tabba Cc: Michael Roth Cc: Isaku Yamahata Signed-off-by: Sean Christopherson Reviewed-by: Kai Huang Message-ID: <20240228024147.41573-10-seanjc@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/mmu/mmu.c | 20 +++++++++++++++----- 1 file changed, 15 insertions(+), 5 deletions(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 9560fca3a6cf6..c5546cd7e1b93 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -4316,11 +4316,6 @@ static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault return RET_PF_EMULATE; } - if (fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn)) { - kvm_mmu_prepare_memory_fault_exit(vcpu, fault); - return -EFAULT; - } - if (fault->is_private) return kvm_faultin_pfn_private(vcpu, fault); @@ -4358,9 +4353,24 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault, { int ret; + /* + * Note that the mmu_invalidate_seq also serves to detect a concurrent + * change in attributes. is_page_fault_stale() will detect an + * invalidation relate to fault->fn and resume the guest without + * installing a mapping in the page tables. + */ fault->mmu_seq = vcpu->kvm->mmu_invalidate_seq; smp_rmb(); + /* + * Now that we have a snapshot of mmu_invalidate_seq we can check for a + * private vs. shared mismatch. + */ + if (fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn)) { + kvm_mmu_prepare_memory_fault_exit(vcpu, fault); + return -EFAULT; + } + /* * Check for a relevant mmu_notifier invalidation event before getting * the pfn from the primary MMU, and before acquiring mmu_lock. -- 2.30.2