| Message ID | 20220810140007.1036293-3-vkuznets@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | i386: KVM: Fix 'system_reset' failures when vCPU is in VMX root operation | expand |
On Wed, 2022-08-10 at 16:00 +0200, Vitaly Kuznetsov wrote: > Setting nested state upon migration needs to happen after kvm_put_sregs2() > to e.g. have EFER.SVME set. This, however, doesn't work for vCPU reset: > when vCPU is in VMX root operation, certain CR bits are locked and > kvm_put_sregs2() may fail. As nested state is fully cleaned up upon > vCPU reset (kvm_arch_reset_vcpu() -> kvm_init_nested_state()), calling > kvm_put_nested_state() before kvm_put_sregs2() is OK, this will ensure > that vCPU is *not* in VMX root opertaion. > > Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> > --- > target/i386/kvm/kvm.c | 20 ++++++++++++++++++-- > 1 file changed, 18 insertions(+), 2 deletions(-) > > diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c > index 4f8dacc1d4b5..73e3880fa57b 100644 > --- a/target/i386/kvm/kvm.c > +++ b/target/i386/kvm/kvm.c > @@ -4529,18 +4529,34 @@ int kvm_arch_put_registers(CPUState *cpu, int level) > > assert(cpu_is_stopped(cpu) || qemu_cpu_is_self(cpu)); > > - /* must be before kvm_put_nested_state so that EFER.SVME is set */ > + /* > + * When resetting a vCPU, make sure to reset nested state first to > + * e.g clear VMXON state and unlock certain CR4 bits. > + */ > + if (level == KVM_PUT_RESET_STATE) { > + ret = kvm_put_nested_state(x86_cpu); > + if (ret < 0) { > + return ret; > + } I should have mentioned this, I actually already debugged the same issue while trying to reproduce the smm int window bug. 100% my fault. I also share the same feeling that this might be yet another 'whack a mole' and break somewhere else, but overall it does make sense. Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com> Best regards, Maxim Levitsky > + } > + > ret = has_sregs2 ? kvm_put_sregs2(x86_cpu) : kvm_put_sregs(x86_cpu); > if (ret < 0) { > return ret; > } > > - if (level >= KVM_PUT_RESET_STATE) { > + /* > + * When putting full CPU state, kvm_put_nested_state() must happen after > + * kvm_put_sregs{,2} so that e.g. EFER.SVME is already set. > + */ > + if (level == KVM_PUT_FULL_STATE) { > ret = kvm_put_nested_state(x86_cpu); > if (ret < 0) { > return ret; > } > + } > > + if (level >= KVM_PUT_RESET_STATE) { > ret = kvm_put_msr_feature_control(x86_cpu); > if (ret < 0) { > return ret;
Maxim Levitsky <mlevitsk@redhat.com> writes: > On Wed, 2022-08-10 at 16:00 +0200, Vitaly Kuznetsov wrote: >> Setting nested state upon migration needs to happen after kvm_put_sregs2() >> to e.g. have EFER.SVME set. This, however, doesn't work for vCPU reset: >> when vCPU is in VMX root operation, certain CR bits are locked and >> kvm_put_sregs2() may fail. As nested state is fully cleaned up upon >> vCPU reset (kvm_arch_reset_vcpu() -> kvm_init_nested_state()), calling >> kvm_put_nested_state() before kvm_put_sregs2() is OK, this will ensure >> that vCPU is *not* in VMX root opertaion. >> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> >> --- >> target/i386/kvm/kvm.c | 20 ++++++++++++++++++-- >> 1 file changed, 18 insertions(+), 2 deletions(-) >> >> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c >> index 4f8dacc1d4b5..73e3880fa57b 100644 >> --- a/target/i386/kvm/kvm.c >> +++ b/target/i386/kvm/kvm.c >> @@ -4529,18 +4529,34 @@ int kvm_arch_put_registers(CPUState *cpu, int level) >> >> assert(cpu_is_stopped(cpu) || qemu_cpu_is_self(cpu)); >> >> - /* must be before kvm_put_nested_state so that EFER.SVME is set */ >> + /* >> + * When resetting a vCPU, make sure to reset nested state first to >> + * e.g clear VMXON state and unlock certain CR4 bits. >> + */ >> + if (level == KVM_PUT_RESET_STATE) { >> + ret = kvm_put_nested_state(x86_cpu); >> + if (ret < 0) { >> + return ret; >> + } > > I should have mentioned this, I actually already debugged the same issue while > trying to reproduce the smm int window bug. > 100% my fault. > > I also share the same feeling that this might be yet another 'whack a mole' and > break somewhere else, but overall it does make sense. This certainly *is* a 'whack a mole' and I'm sure there are other cases when one of calls in kvm_arch_put_registers() fails. We need to work on what's missing so we can expose kvm_vcpu_reset() to VMMs. > > > Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com> > Thanks!
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c index 4f8dacc1d4b5..73e3880fa57b 100644 --- a/target/i386/kvm/kvm.c +++ b/target/i386/kvm/kvm.c @@ -4529,18 +4529,34 @@ int kvm_arch_put_registers(CPUState *cpu, int level) assert(cpu_is_stopped(cpu) || qemu_cpu_is_self(cpu)); - /* must be before kvm_put_nested_state so that EFER.SVME is set */ + /* + * When resetting a vCPU, make sure to reset nested state first to + * e.g clear VMXON state and unlock certain CR4 bits. + */ + if (level == KVM_PUT_RESET_STATE) { + ret = kvm_put_nested_state(x86_cpu); + if (ret < 0) { + return ret; + } + } + ret = has_sregs2 ? kvm_put_sregs2(x86_cpu) : kvm_put_sregs(x86_cpu); if (ret < 0) { return ret; } - if (level >= KVM_PUT_RESET_STATE) { + /* + * When putting full CPU state, kvm_put_nested_state() must happen after + * kvm_put_sregs{,2} so that e.g. EFER.SVME is already set. + */ + if (level == KVM_PUT_FULL_STATE) { ret = kvm_put_nested_state(x86_cpu); if (ret < 0) { return ret; } + } + if (level >= KVM_PUT_RESET_STATE) { ret = kvm_put_msr_feature_control(x86_cpu); if (ret < 0) { return ret;
Setting nested state upon migration needs to happen after kvm_put_sregs2() to e.g. have EFER.SVME set. This, however, doesn't work for vCPU reset: when vCPU is in VMX root operation, certain CR bits are locked and kvm_put_sregs2() may fail. As nested state is fully cleaned up upon vCPU reset (kvm_arch_reset_vcpu() -> kvm_init_nested_state()), calling kvm_put_nested_state() before kvm_put_sregs2() is OK, this will ensure that vCPU is *not* in VMX root opertaion. Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> --- target/i386/kvm/kvm.c | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-)