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authorPeter Shier <pshier@google.com>2020-08-20 16:05:45 -0700
committerPaolo Bonzini <pbonzini@redhat.com>2020-09-11 13:15:09 -0400
commit43fea4e42599c3eb4109996698f5c25761d3f815 (patch)
treea96050499c41cab0e291ed2ad2d26b184161ff90 /virt
parent1b67fd086dd7be076f190dfe4b52403d0cf58375 (diff)
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 <pshier@google.com> Reviewed-by: Jim Mattson <jmattson@google.com> Message-Id: <20200820230545.2411347-1-pshier@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'virt')
0 files changed, 0 insertions, 0 deletions