From b6162e82aef19fee9c32cb3fe9ac30d9116a8c73 Mon Sep 17 00:00:00 2001 From: Vitaly Kuznetsov Date: Wed, 27 May 2020 11:01:02 +0200 Subject: [PATCH] KVM: nSVM: Preserve registers modifications done before nested_svm_vmexit() L2 guest hang is observed after 'exit_required' was dropped and nSVM switched to check_nested_events() completely. The hang is a busy loop when e.g. KVM is emulating an instruction (e.g. L2 is accessing MMIO space and we drop to userspace). After nested_svm_vmexit() and when L1 is doing VMRUN nested guest's RIP is not advanced so KVM goes into emulating the same instruction which caused nested_svm_vmexit() and the loop continues. nested_svm_vmexit() is not new, however, with check_nested_events() we're now calling it later than before. In case by that time KVM has modified register state we may pick stale values from VMCB when trying to save nested guest state to nested VMCB. nVMX code handles this case correctly: sync_vmcs02_to_vmcs12() called from nested_vmx_vmexit() does e.g 'vmcs12->guest_rip = kvm_rip_read(vcpu)' and this ensures KVM-made modifications are preserved. Do the same for nSVM. Generally, nested_vmx_vmexit()/nested_svm_vmexit() need to pick up all nested guest state modifications done by KVM after vmexit. It would be great to find a way to express this in a way which would not require to manually track these changes, e.g. nested_{vmcb,vmcs}_get_field(). Co-debugged-with: Paolo Bonzini Signed-off-by: Vitaly Kuznetsov Message-Id: <20200527090102.220647-1-vkuznets@redhat.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/svm/nested.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c index d544cce4f964..f39e0d578b9b 100644 --- a/arch/x86/kvm/svm/nested.c +++ b/arch/x86/kvm/svm/nested.c @@ -491,9 +491,9 @@ int nested_svm_vmexit(struct vcpu_svm *svm) nested_vmcb->save.cr2 = vmcb->save.cr2; nested_vmcb->save.cr4 = svm->vcpu.arch.cr4; nested_vmcb->save.rflags = kvm_get_rflags(&svm->vcpu); - nested_vmcb->save.rip = vmcb->save.rip; - nested_vmcb->save.rsp = vmcb->save.rsp; - nested_vmcb->save.rax = vmcb->save.rax; + nested_vmcb->save.rip = kvm_rip_read(&svm->vcpu); + nested_vmcb->save.rsp = kvm_rsp_read(&svm->vcpu); + nested_vmcb->save.rax = kvm_rax_read(&svm->vcpu); nested_vmcb->save.dr7 = vmcb->save.dr7; nested_vmcb->save.dr6 = svm->vcpu.arch.dr6; nested_vmcb->save.cpl = vmcb->save.cpl;