Re: [PATCH RFC v1 1/2] i386: reset KVM nested state upon CPU reset

[Maxim Levitsky]

On Wed, 2022-08-10 at 16:00 +0200, Vitaly Kuznetsov wrote:
> Make sure env->nested_state is cleaned up when a vCPU is reset, it may
> be stale after an incoming migration, kvm_arch_put_registers() may
> end up failing or putting vCPU in a weird state.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
>  target/i386/kvm/kvm.c | 37 +++++++++++++++++++++++++++----------
>  1 file changed, 27 insertions(+), 10 deletions(-)
> 
> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
> index f148a6d52fa4..4f8dacc1d4b5 100644
> --- a/target/i386/kvm/kvm.c
> +++ b/target/i386/kvm/kvm.c
> @@ -1695,6 +1695,30 @@ static void kvm_init_xsave(CPUX86State *env)
>             env->xsave_buf_len);
>  }
>  
> +static void kvm_init_nested_state(CPUX86State *env)
> +{
> +    struct kvm_vmx_nested_state_hdr *vmx_hdr;
> +    uint32_t size;
> +
> +    if (!env->nested_state) {
> +        return;
> +    }
> +
> +    size = env->nested_state->size;
> +
> +    memset(env->nested_state, 0, size);
> +    env->nested_state->size = size;
> +
> +    if (cpu_has_vmx(env)) {
> +        env->nested_state->format = KVM_STATE_NESTED_FORMAT_VMX;
> +        vmx_hdr = &env->nested_state->hdr.vmx;
> +        vmx_hdr->vmxon_pa = -1ull;
> +        vmx_hdr->vmcs12_pa = -1ull;
> +    } else if (cpu_has_svm(env)) {
> +        env->nested_state->format = KVM_STATE_NESTED_FORMAT_SVM;
> +    }
> +}
> +
>  int kvm_arch_init_vcpu(CPUState *cs)
>  {
>      struct {
> @@ -2122,19 +2146,10 @@ int kvm_arch_init_vcpu(CPUState *cs)
>          assert(max_nested_state_len >= offsetof(struct kvm_nested_state, 
> data));
>  
>          if (cpu_has_vmx(env) || cpu_has_svm(env)) {
> -            struct kvm_vmx_nested_state_hdr *vmx_hdr;
> -
>              env->nested_state = g_malloc0(max_nested_state_len);
>              env->nested_state->size = max_nested_state_len;
>  
> -            if (cpu_has_vmx(env)) {
> -                env->nested_state->format = KVM_STATE_NESTED_FORMAT_VMX;
> -                vmx_hdr = &env->nested_state->hdr.vmx;
> -                vmx_hdr->vmxon_pa = -1ull;
> -                vmx_hdr->vmcs12_pa = -1ull;
> -            } else {
> -                env->nested_state->format = KVM_STATE_NESTED_FORMAT_SVM;
> -            }
> +            kvm_init_nested_state(env);
>          }
>      }
>  
> @@ -2199,6 +2214,8 @@ void kvm_arch_reset_vcpu(X86CPU *cpu)
>      /* enabled by default */
>      env->poll_control_msr = 1;
>  
> +    kvm_init_nested_state(env);
> +
>      sev_es_set_reset_vector(CPU(cpu));
>  }
>  
Makes sense.

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
        Maxim Levitsky