RE: [PATCH Part2 v6 24/49] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_START command

Kalra, Ashish
2022-06-24T18:17:50Z

[AMD Official Use Only - General]

>> +static int snp_decommission_context(struct kvm *kvm) {
>> + struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
>> + struct sev_data_snp_decommission 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 = snp_guest_decommission(&data, NULL);

>Do we have a similar race like in sev_unbind_asid() with DEACTIVATE and WBINVD/DF_FLUSH? The SNP_DECOMMISSION spec looks quite similar to DEACTIVATE.

Yes, SNP_DECOMMISION also marks the ASID as invalid and require a WBINVD/DF_FLUSH before the ASID is re-used/re-cycled, so we need to prevent against
DECOMMISION and ASID re-cycling happening at the same time. Can reuse the same RWSEM (sev_deactivate_lock) here too.

Thanks,
Ashish

> + 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;
> +}
> +
> void sev_vm_destroy(struct kvm *kvm)
> {
> struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;