Re: [PATCH v2 for-8.2?] i386/sev: Avoid SEV-ES crash due to missing MSR_EFER_LMA bit

[Paolo Bonzini <pbonzini@redhat.com>]

On Tue, Dec 5, 2023 at 11:28 PM Michael Roth <michael.roth@amd.com> wrote:
> @@ -3637,12 +3638,18 @@ static int kvm_get_sregs(X86CPU *cpu)
>      env->gdt.limit = sregs.gdt.limit;
>      env->gdt.base = sregs.gdt.base;
>
> +    cr0_old = env->cr[0];
>      env->cr[0] = sregs.cr0;
>      env->cr[2] = sregs.cr2;
>      env->cr[3] = sregs.cr3;
>      env->cr[4] = sregs.cr4;
>
>      env->efer = sregs.efer;
> +    if (sev_es_enabled() && env->efer & MSR_EFER_LME) {
> +        if (!(cr0_old & CR0_PG_MASK) && env->cr[0] & CR0_PG_MASK) {
> +            env->efer |= MSR_EFER_LMA;
> +        }
> +    }

There is no need to check cr0_old or sev_es_enabled(); EFER.LMA is
simply EFER.LME && CR0.PG.

Alternatively, sev_es_enabled() could be an assertion, that is:

    if ((env->efer & MSR_EFER_LME) && (env->cr[0] & CR0_PG_MASK) &&
       !(env->efer & MSR_EFER_LMA)) {
        /* Workaround for... */
        assert(sev_es_enabled());
        env->efer |= MSR_EFER_LMA;
    }

What do you think?

Thanks,

Paolo

>      /* changes to apic base and cr8/tpr are read back via kvm_arch_post_run */
>      x86_update_hflags(env);
> @@ -3654,6 +3661,7 @@ static int kvm_get_sregs2(X86CPU *cpu)
>  {
>      CPUX86State *env = &cpu->env;
>      struct kvm_sregs2 sregs;
> +    target_ulong cr0_old;
>      int i, ret;
>
>      ret = kvm_vcpu_ioctl(CPU(cpu), KVM_GET_SREGS2, &sregs);
> @@ -3676,12 +3684,18 @@ static int kvm_get_sregs2(X86CPU *cpu)
>      env->gdt.limit = sregs.gdt.limit;
>      env->gdt.base = sregs.gdt.base;
>
> +    cr0_old = env->cr[0];
>      env->cr[0] = sregs.cr0;
>      env->cr[2] = sregs.cr2;
>      env->cr[3] = sregs.cr3;
>      env->cr[4] = sregs.cr4;
>
>      env->efer = sregs.efer;
> +    if (sev_es_enabled() && env->efer & MSR_EFER_LME) {
> +        if (!(cr0_old & CR0_PG_MASK) && env->cr[0] & CR0_PG_MASK) {
> +            env->efer |= MSR_EFER_LMA;
> +        }
> +    }
>
>      env->pdptrs_valid = sregs.flags & KVM_SREGS2_FLAGS_PDPTRS_VALID;
>
> --
> 2.25.1
>