From 43fea4e42599c3eb4109996698f5c25761d3f815 Mon Sep 17 00:00:00 2001 From: Peter Shier Date: Thu, 20 Aug 2020 16:05:45 -0700 Subject: [PATCH] KVM: nVMX: Update VMCS02 when L2 PAE PDPTE updates detected When L2 uses PAE, L0 intercepts of L2 writes to CR0/CR3/CR4 call load_pdptrs to read the possibly updated PDPTEs from the guest physical address referenced by CR3. It loads them into vcpu->arch.walk_mmu->pdptrs and sets VCPU_EXREG_PDPTR in vcpu->arch.regs_dirty. At the subsequent assumed reentry into L2, the mmu will call vmx_load_mmu_pgd which calls ept_load_pdptrs. ept_load_pdptrs sees VCPU_EXREG_PDPTR set in vcpu->arch.regs_dirty and loads VMCS02.GUEST_PDPTRn from vcpu->arch.walk_mmu->pdptrs[]. This all works if the L2 CRn write intercept always resumes L2. The resume path calls vmx_check_nested_events which checks for exceptions, MTF, and expired VMX preemption timers. If vmx_check_nested_events finds any of these conditions pending it will reflect the corresponding exit into L1. Live migration at this point would also cause a missed immediate reentry into L2. After L1 exits, vmx_vcpu_run calls vmx_register_cache_reset which clears VCPU_EXREG_PDPTR in vcpu->arch.regs_dirty. When L2 next resumes, ept_load_pdptrs finds VCPU_EXREG_PDPTR clear in vcpu->arch.regs_dirty and does not load VMCS02.GUEST_PDPTRn from vcpu->arch.walk_mmu->pdptrs[]. prepare_vmcs02 will then load VMCS02.GUEST_PDPTRn from vmcs12->pdptr0/1/2/3 which contain the stale values stored at last L2 exit. A repro of this bug showed L2 entering triple fault immediately due to the bad VMCS02.GUEST_PDPTRn values. When L2 is in PAE paging mode add a call to ept_load_pdptrs before leaving L2. This will update VMCS02.GUEST_PDPTRn if they are dirty in vcpu->arch.walk_mmu->pdptrs[]. Tested: kvm-unit-tests with new directed test: vmx_mtf_pdpte_test. Verified that test fails without the fix. Also ran Google internal VMM with an Ubuntu 16.04 4.4.0-83 guest running a custom hypervisor with a 32-bit Windows XP L2 guest using PAE. Prior to fix would repro readily. Ran 14 simultaneous L2s for 140 iterations with no failures. Signed-off-by: Peter Shier Reviewed-by: Jim Mattson Message-Id: <20200820230545.2411347-1-pshier@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/vmx/nested.c | 8 ++++++++ arch/x86/kvm/vmx/vmx.c | 4 ++-- arch/x86/kvm/vmx/vmx.h | 1 + 3 files changed, 11 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index 23b58c28a1c9..d7482ccf6a8d 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -4404,6 +4404,14 @@ void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 vm_exit_reason, if (kvm_check_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu)) kvm_vcpu_flush_tlb_current(vcpu); + /* + * VCPU_EXREG_PDPTR will be clobbered in arch/x86/kvm/vmx/vmx.h between + * now and the new vmentry. Ensure that the VMCS02 PDPTR fields are + * up-to-date before switching to L1. + */ + if (enable_ept && is_pae_paging(vcpu)) + vmx_ept_load_pdptrs(vcpu); + leave_guest_mode(vcpu); if (nested_cpu_has_preemption_timer(vmcs12)) diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 46ba2e03a892..19a599bebd5c 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -2971,7 +2971,7 @@ static void vmx_flush_tlb_guest(struct kvm_vcpu *vcpu) vpid_sync_context(to_vmx(vcpu)->vpid); } -static void ept_load_pdptrs(struct kvm_vcpu *vcpu) +void vmx_ept_load_pdptrs(struct kvm_vcpu *vcpu) { struct kvm_mmu *mmu = vcpu->arch.walk_mmu; @@ -3114,7 +3114,7 @@ static void vmx_load_mmu_pgd(struct kvm_vcpu *vcpu, unsigned long pgd, guest_cr3 = vcpu->arch.cr3; else /* vmcs01.GUEST_CR3 is already up-to-date. */ update_guest_cr3 = false; - ept_load_pdptrs(vcpu); + vmx_ept_load_pdptrs(vcpu); } else { guest_cr3 = pgd; } diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h index 26175a4759fa..a2f82127c170 100644 --- a/arch/x86/kvm/vmx/vmx.h +++ b/arch/x86/kvm/vmx/vmx.h @@ -356,6 +356,7 @@ void vmx_update_host_rsp(struct vcpu_vmx *vmx, unsigned long host_rsp); int vmx_find_msr_index(struct vmx_msrs *m, u32 msr); int vmx_handle_memory_failure(struct kvm_vcpu *vcpu, int r, struct x86_exception *e); +void vmx_ept_load_pdptrs(struct kvm_vcpu *vcpu); #define POSTED_INTR_ON 0 #define POSTED_INTR_SN 1