Cc'ing Max :-) At first glance the condition in vmx_set_nested_state() is correct so I guess we either have a stale KVM_STATE_NESTED_RUN_PENDING when in SMM or stale smm.flags when outside of it... Philippe Mathieu-Daudé <philmd@xxxxxxxxxx> writes: > 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, >> >> Eiichi >> >>> On 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 >>> >> >> > -- Vitaly
