Re: [PATCH RFC v8 34/56] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_START command

[Tom Lendacky]

On 4/26/23 12:06, Sabin Rapan wrote:
> On 20.02.2023 20:38, Michael Roth wrote:
> > From: Brijesh Singh <brijesh.singh@xxxxxxx>
> >
> >   
> > +static int snp_decommission_context(struct kvm *kvm)
> > +{
> > +	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> > +	struct sev_data_snp_addr data = {};
> > +	int ret;
> > +
> > +	/* If context is not created then do nothing */
> > +	if (!sev->snp_context)
> > +		return 0;
> > +
> > +	data.gctx_paddr = __sme_pa(sev->snp_context);
> > +	ret = sev_do_cmd(SEV_CMD_SNP_DECOMMISSION, &data, NULL);
> > +	if (WARN_ONCE(ret, "failed to release guest context"))
> > +		return ret;
> > +
> > +	/* free the context page now */
> > +	snp_free_firmware_page(sev->snp_context);
> > +	sev->snp_context = NULL;
> > +
> > +	return 0;
> > +}
> > +
>
> Even though it's not documented, SNP_DECOMMISSION seems to clear the
> WBINVD indicator just like DEACTIVATE does for SEV.
> Won't ASID recycling race with SNP_DECOMMISSION if the latter isn't
> guarded with sev_deactivate_lock?

Good catch, yes, this needs to use the sev_deactivate_lock around the 
DECOMMISSION command.

Thanks,
Tom

> >   void sev_vm_destroy(struct kvm *kvm)
> >   {
> >   	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> > @@ -2333,7 +2440,15 @@ void sev_vm_destroy(struct kvm *kvm)
> >   		}
> >   	}
> >   
> > -	sev_unbind_asid(kvm, sev->handle);
> > +	if (sev_snp_guest(kvm)) {
> > +		if (snp_decommission_context(kvm)) {
> > +			WARN_ONCE(1, "Failed to free SNP guest context, leaking asid!\n");
> > +			return;
> > +		}
> > +	} else {
> > +		sev_unbind_asid(kvm, sev->handle);
> > +	}
> > +
> >   	sev_asid_free(sev);
> >   }
> >   
>
>
>
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