linux-kernel - Re: [PATCH RFC v8 34/56] KVM: SVM: Add KVM_SEV_SNP_LAUNCH

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Message-ID: <f708da54-b99c-2ce8-f68f-6f3ba28ec2ff@amazon.com>
Date:   Wed, 26 Apr 2023 20:06:33 +0300
From:   Sabin Rapan <sabrapan@...zon.com>
To:     Michael Roth <michael.roth@....com>, <kvm@...r.kernel.org>
CC:     <linux-coco@...ts.linux.dev>, <linux-mm@...ck.org>,
        <linux-crypto@...r.kernel.org>, <x86@...nel.org>,
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        <ashish.kalra@....com>, <nikunj.dadhania@....com>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH RFC v8 34/56] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_START
 command



On 20.02.2023 20:38, Michael Roth wrote:
> From: Brijesh Singh <brijesh.singh@....com>
> 
>  
> +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?


>  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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