linux-kernel - Re: [PATCH v7 01/10] KVM: SEV: Disable SEV-SNP support on initialization failure

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Message-ID: <9480ce1b-2c35-499c-b60f-1c02ea9cdc16@amd.com>
Date: Tue, 25 Feb 2025 10:41:37 -0600
From: "Pratik R. Sampat" <prsampat@....com>
To: Tom Lendacky <thomas.lendacky@....com>, <linux-kernel@...r.kernel.org>,
	<x86@...nel.org>, <kvm@...r.kernel.org>, <linux-crypto@...r.kernel.org>,
	<linux-kselftest@...r.kernel.org>
CC: <seanjc@...gle.com>, <pbonzini@...hat.com>, <tglx@...utronix.de>,
	<mingo@...hat.com>, <bp@...en8.de>, <dave.hansen@...ux.intel.com>,
	<shuah@...nel.org>, <pgonda@...gle.com>, <ashish.kalra@....com>,
	<nikunj@....com>, <pankaj.gupta@....com>, <michael.roth@....com>,
	<sraithal@....com>
Subject: Re: [PATCH v7 01/10] KVM: SEV: Disable SEV-SNP support on
 initialization failure

Hi Tom,

On 2/24/2025 3:28 PM, Tom Lendacky wrote:
> On 2/21/25 15:01, Pratik R. Sampat wrote:
>> During platform init, SNP initialization may fail for several reasons,
>> such as firmware command failures and incompatible versions. However,
>> the KVM capability may continue to advertise support for it. Export this
>> information to KVM and withdraw SEV-SNP support if has not been
>> successfully initialized.
> 
> Hmmm... rather than creating a new API, can you just issue an
> SNP_PLATFORM_STATUS command and see if the SNP is not in the UNINIT state?
> 

Although reading sev->snp_initialized is probably cheaper to do, it is
cleaner to query the platform status.

Querying SNP_PLATFORM_STATUS requires the pages to transition to
firmware-owned and back, and the helpers for it are implemented within
sev-dev.c. So, similar to sev_platform_status(), I'm thinking it is
probably better to create the snp_platform_status() API as well and use
that within KVM to check the state.

Thanks!
Pratik