Re: [PATCH] KVM: fix CPU reset wrt HF2_GIF_MASK

[Jan Kiszka]

On 23.07.20 16:27, Vitaly Kuznetsov wrote:
> HF2_GIF_MASK is set in env->hflags2 unconditionally on CPU reset
> (see x86_cpu_reset()) but when calling KVM_SET_NESTED_STATE,
> KVM_STATE_NESTED_GIF_SET is only valid for nSVM as e.g. nVMX code
> looks like
>
> if (kvm_state->hdr.vmx.vmxon_pa == -1ull) {
>      if (kvm_state->flags & ~KVM_STATE_NESTED_EVMCS)
>          return -EINVAL;
> }
>
> Also, when adjusting the environment after KVM_GET_NESTED_STATE we
> need not reset HF2_GIF_MASK on VMX as e.g. x86_cpu_pending_interrupt()
> expects it to be set.
>
> Alternatively, we could've made env->hflags2 SVM-only.
>
> Reported-by: Jan Kiszka <jan.kiszka@siemens.com>
> Fixes: b16c0e20c742 ("KVM: add support for AMD nested live migration")
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
>   target/i386/kvm.c | 16 +++++++++++-----
>   1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> index 2b6b7443d273..3c4647fbfbf6 100644
> --- a/target/i386/kvm.c
> +++ b/target/i386/kvm.c
> @@ -3883,7 +3883,9 @@ static int kvm_put_nested_state(X86CPU *cpu)
>       } else {
>           env->nested_state->flags &= ~KVM_STATE_NESTED_GUEST_MODE;
>       }
> -    if (env->hflags2 & HF2_GIF_MASK) {
> +
> +    /* Don't set KVM_STATE_NESTED_GIF_SET on VMX as it is illegal */
> +    if (cpu_has_svm(env) && (env->hflags2 & HF2_GIF_MASK)) {
>           env->nested_state->flags |= KVM_STATE_NESTED_GIF_SET;
>       } else {
>           env->nested_state->flags &= ~KVM_STATE_NESTED_GIF_SET;
> @@ -3925,10 +3927,14 @@ static int kvm_get_nested_state(X86CPU *cpu)
>       } else {
>           env->hflags &= ~HF_GUEST_MASK;
>       }
> -    if (env->nested_state->flags & KVM_STATE_NESTED_GIF_SET) {
> -        env->hflags2 |= HF2_GIF_MASK;
> -    } else {
> -        env->hflags2 &= ~HF2_GIF_MASK;
> +
> +    /* Keep HF2_GIF_MASK set on !SVM as x86_cpu_pending_interrupt() needs it */
> +    if (cpu_has_svm(env)) {
> +        if (env->nested_state->flags & KVM_STATE_NESTED_GIF_SET) {
> +            env->hflags2 |= HF2_GIF_MASK;
> +        } else {
> +            env->hflags2 &= ~HF2_GIF_MASK;
> +        }
>       }
>   
>       return ret;

Tested-by: Jan Kiszka <jan.kiszka@siemens.com>

Thanks!
Jan

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