While KVM's MMU should be fully reset by loading of nested CR0/CR3/CR4 by KVM_SET_SREGS, we are not in nested mode yet when we do it and therefore only root_mmu is reset. On regular nested entries we call nested_svm_load_cr3 which both updates the guest's CR3 in the MMU when it is needed, and it also initializes the mmu again which makes it initialize the walk_mmu as well when nested paging is enabled in both host and guest. Since we don't call nested_svm_load_cr3 on nested state load, the walk_mmu can be left uninitialized, which can lead to a NULL pointer dereference while accessing it if we happen to get a nested page fault right after entering the nested guest first time after the migration and we decide to emulate it, which leads to the emulator trying to access walk_mmu->gva_to_gpa which is NULL. Therefore we should call this function on nested state load as well. Suggested-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx> --- arch/x86/kvm/svm/nested.c | 40 +++++++++++++++++++++------------------ 1 file changed, 22 insertions(+), 18 deletions(-) diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c index 8523f60adb92..ac5e3e17bda4 100644 --- a/arch/x86/kvm/svm/nested.c +++ b/arch/x86/kvm/svm/nested.c @@ -215,24 +215,6 @@ static bool nested_svm_vmrun_msrpm(struct vcpu_svm *svm) return true; } -static bool svm_get_nested_state_pages(struct kvm_vcpu *vcpu) -{ - struct vcpu_svm *svm = to_svm(vcpu); - - if (WARN_ON(!is_guest_mode(vcpu))) - return true; - - if (!nested_svm_vmrun_msrpm(svm)) { - vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR; - vcpu->run->internal.suberror = - KVM_INTERNAL_ERROR_EMULATION; - vcpu->run->internal.ndata = 0; - return false; - } - - return true; -} - static bool nested_vmcb_check_controls(struct vmcb_control_area *control) { if (CC(!vmcb_is_intercept(control, INTERCEPT_VMRUN))) @@ -1312,6 +1294,28 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu, return ret; } +static bool svm_get_nested_state_pages(struct kvm_vcpu *vcpu) +{ + struct vcpu_svm *svm = to_svm(vcpu); + + if (WARN_ON(!is_guest_mode(vcpu))) + return true; + + if (nested_svm_load_cr3(&svm->vcpu, vcpu->arch.cr3, + nested_npt_enabled(svm))) + return false; + + if (!nested_svm_vmrun_msrpm(svm)) { + vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR; + vcpu->run->internal.suberror = + KVM_INTERNAL_ERROR_EMULATION; + vcpu->run->internal.ndata = 0; + return false; + } + + return true; +} + struct kvm_x86_nested_ops svm_nested_ops = { .check_events = svm_check_nested_events, .triple_fault = nested_svm_triple_fault, -- 2.26.2