linux-kernel - Re: [PATCH 0/2] Remove some hardcoded SEV-SNP guest policy checks during guest launch

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Message-ID: <691a453e-768f-1302-1db7-225b1086391d@amd.com>
Date: Tue, 24 Jun 2025 15:31:06 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: Sean Christopherson <seanjc@...gle.com>, kvm@...r.kernel.org,
 linux-kernel@...r.kernel.org, x86@...nel.org
Cc: Paolo Bonzini <pbonzini@...hat.com>, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>, Ingo Molnar <mingo@...hat.com>,
 Thomas Gleixner <tglx@...utronix.de>, Michael Roth <michael.roth@....com>
Subject: Re: [PATCH 0/2] Remove some hardcoded SEV-SNP guest policy checks
 during guest launch

On 6/24/25 14:38, Sean Christopherson wrote:
> On Thu, 29 May 2025 16:17:58 -0500, Tom Lendacky wrote:
>> This series removes some guest policy checks that can be better controlled
>> by the SEV firmware.
>>
>> - Remove the check for the SMT policy bit. Currently, a check is made to
>>   ensure the SMT policy bit is set to 1. However, there is no reason for
>>   KVM to do this. The SMT policy bit, when 0, is used to ensure that SMT
>>   has been disabled *in the BIOS.* As this does not require any special
>>   support within KVM, the check can be safely removed to allow the SEV
>>   firmware to determine whether the system meets the policy.
>>
>> [...]
> 
> Applied to kvm-x86 svm.  FWIW, I'm not entirely sure I love the idea of doing
> nothing, e.g. it'd be nice to enumerate support to userspace.  But adding a
> bunch of code to regurgitate information that's likely available to userspace
> (or more likely, the platform admin/orchestrator) doesn't seem worthwile either.
> 
> I'll make sure to flag this for Paolo's eyeballs.

Sounds good, thanks Sean!

Tom

> 
> [1/2] KVM: SVM: Allow SNP guest policy disallow running with SMT enabled
>       https://github.com/kvm-x86/linux/commit/9f4701e05fae
> [2/2] KVM: SVM: Allow SNP guest policy to specify SINGLE_SOCKET
>       https://github.com/kvm-x86/linux/commit/24be2b7956a5
> 
> --
> https://github.com/kvm-x86/kvm-unit-tests/tree/next