Cc'ing Vitaly. On 26/10/23 07:49, Eiichi Tsukata wrote:
Hi all, Here is additional details on the issue. We've found this issue when testing Windows Virtual Secure Mode (VSM) VMs. We sometimes saw live migration failures of VSM-enabled VMs. It turned out that the issue happens during live migration when VMs change boot related EFI variables (ex: BootOrder, Boot0001). After some debugging, I've found the race I mentioned in the commit message. Symptom ======= When it happnes with the latest Qemu which has commit https://github.com/qemu/qemu/commit/7191f24c7fcfbc1216d09 Qemu shows the following error message on destination. qemu-system-x86_64: Failed to put registers after init: Invalid argument If it happens with older Qemu which doesn't have the commit, then we see CPU dump something like this: KVM internal error. Suberror: 3 extra data[0]: 0x0000000080000b0e extra data[1]: 0x0000000000000031 extra data[2]: 0x0000000000000683 extra data[3]: 0x000000007f809000 extra data[4]: 0x0000000000000026 RAX=0000000000000000 RBX=0000000000000000 RCX=0000000000000000 RDX=0000000000000f61 RSI=0000000000000000 RDI=0000000000000000 RBP=0000000000000000 RSP=0000000000000000 R8 =0000000000000000 R9 =0000000000000000 R10=0000000000000000 R11=0000000000000000 R12=0000000000000000 R13=0000000000000000 R14=0000000000000000 R15=0000000000000000 RIP=000000000000fff0 RFL=00010002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0 ES =0020 0000000000000000 ffffffff 00c09300 DPL=0 DS [-WA] CS =0038 0000000000000000 ffffffff 00a09b00 DPL=0 CS64 [-RA] SS =0020 0000000000000000 ffffffff 00c09300 DPL=0 DS [-WA] DS =0020 0000000000000000 ffffffff 00c09300 DPL=0 DS [-WA] FS =0020 0000000000000000 ffffffff 00c09300 DPL=0 DS [-WA] GS =0020 0000000000000000 ffffffff 00c09300 DPL=0 DS [-WA] LDT=0000 0000000000000000 ffffffff 00c00000 TR =0040 000000007f7df050 00068fff 00808b00 DPL=0 TSS64-busy GDT= 000000007f7df000 0000004f IDT= 000000007f836000 000001ff CR0=80010033 CR2=000000000000fff0 CR3=000000007f809000 CR4=00000668 DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 DR6=00000000ffff0ff0 DR7=0000000000000400 EFER=0000000000000d00 Code=?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? <??> ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? In the above dump, CR3 is pointing to SMRAM region though SMM=0. Repro ===== Repro step is pretty simple. * Run SMM enabled Linux guest with secure boot enabled OVMF. * Run the following script in the guest. /usr/libexec/qemu-kvm & while true do efibootmgr -n 1 done * Do live migration On my environment, live migration fails in 20%. VMX specific ============ This issue is VMX sepcific and SVM is not affected as the validation in svm_set_nested_state() is a bit different from VMX one. VMX: static int vmx_set_nested_state(struct kvm_vcpu *vcpu, struct kvm_nested_state __user *user_kvm_nested_state, struct kvm_nested_state *kvm_state) { .. /* * SMM temporarily disables VMX, so we cannot be in guest mode, * nor can VMLAUNCH/VMRESUME be pending. Outside SMM, SMM flags * must be zero. */ if (is_smm(vcpu) ? (kvm_state->flags & (KVM_STATE_NESTED_GUEST_MODE | KVM_STATE_NESTED_RUN_PENDING)) : kvm_state->hdr.vmx.smm.flags) return -EINVAL; .. SVM: static int svm_set_nested_state(struct kvm_vcpu *vcpu, struct kvm_nested_state __user *user_kvm_nested_state, struct kvm_nested_state *kvm_state) { .. /* SMM temporarily disables SVM, so we cannot be in guest mode. */ if (is_smm(vcpu) && (kvm_state->flags & KVM_STATE_NESTED_GUEST_MODE)) return -EINVAL; .. Thanks, EiichiOn Oct 26, 2023, at 14:42, Eiichi Tsukata <eiichi.tsukata@xxxxxxxxxxx> wrote: kvm_put_vcpu_events() needs to be called before kvm_put_nested_state() because vCPU's hflag is referred in KVM vmx_get_nested_state() validation. Otherwise kvm_put_nested_state() can fail with -EINVAL when a vCPU is in VMX operation and enters SMM mode. This leads to live migration failure. Signed-off-by: Eiichi Tsukata <eiichi.tsukata@xxxxxxxxxxx> --- target/i386/kvm/kvm.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c index e7c054cc16..cd635c9142 100644 --- a/target/i386/kvm/kvm.c +++ b/target/i386/kvm/kvm.c @@ -4741,6 +4741,15 @@ int kvm_arch_put_registers(CPUState *cpu, int level) return ret; } + /* + * must be before kvm_put_nested_state so that HF_SMM_MASK is set during + * SMM. + */ + ret = kvm_put_vcpu_events(x86_cpu, level); + if (ret < 0) { + return ret; + } + if (level >= KVM_PUT_RESET_STATE) { ret = kvm_put_nested_state(x86_cpu); if (ret < 0) { @@ -4787,10 +4796,6 @@ int kvm_arch_put_registers(CPUState *cpu, int level) if (ret < 0) { return ret; } - ret = kvm_put_vcpu_events(x86_cpu, level); - if (ret < 0) { - return ret; - } if (level >= KVM_PUT_RESET_STATE) { ret = kvm_put_mp_state(x86_cpu); if (ret < 0) { -- 2.41.0
