linux-kernel - Re: [PATCH v3 2/9] KVM: selftests: Add a basic SNP smoke test

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Message-ID: <ZyJzcOCPJstrumbE@google.com>
Date: Wed, 30 Oct 2024 10:57:04 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: "Pratik R. Sampat" <pratikrajesh.sampat@....com>
Cc: kvm@...r.kernel.org, pbonzini@...hat.com, pgonda@...gle.com, 
	thomas.lendacky@....com, michael.roth@....com, shuah@...nel.org, 
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/9] KVM: selftests: Add a basic SNP smoke test

On Wed, Oct 30, 2024, Pratik R. Sampat wrote:
> On 10/30/2024 8:46 AM, Sean Christopherson wrote:
> > +/* Minimum firmware version required for the SEV-SNP support */
> > +#define SNP_FW_REQ_VER_MAJOR   1
> > +#define SNP_FW_REQ_VER_MINOR   51
> > 
> > Side topic, why are these hardcoded?  And where did they come from?  If they're
> > arbitrary KVM selftests values, make that super duper clear.
> 
> Well, it's not entirely arbitrary. This was the version that SNP GA'd
> with first so that kind of became the minimum required version needed.
> 
> I think the only place we've documented this is here -
> https://github.com/AMDESE/AMDSEV/tree/snp-latest?tab=readme-ov-file#upgrade-sev-firmware.
> 
> Maybe, I can modify the comment above to say something like -
> Minimum general availability release firmware required for SEV-SNP support.

Hmm, so if AMD says SNP is only supported for firmware version >= 1.51, why on
earth is that not checked and enforced by the kernel?  Relying on userspace to
not crash the host (or worse) because of unsupported firmware is not a winning
strategy.