Maxim Levitsky <mlevi...@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 <vkuzn...@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 <mlevi...@redhat.com> > Thanks! -- Vitaly