linux-kernel - Re: [PATCH v11 0/8] KVM: SVM: Enable Secure TSC for SEV-SNP

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Message-ID: <aKXld8Lecq7tjYZS@google.com>
Date: Wed, 20 Aug 2025 08:10:47 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: "Nikunj A. Dadhania" <nikunj@....com>
Cc: Kai Huang <kai.huang@...el.com>, "pbonzini@...hat.com" <pbonzini@...hat.com>, 
	"thomas.lendacky@....com" <thomas.lendacky@....com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>, 
	"vaishali.thakkar@...e.com" <vaishali.thakkar@...e.com>, 
	"Ketan.Chaturvedi@....com" <Ketan.Chaturvedi@....com>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"michael.roth@....com" <michael.roth@....com>, "bp@...en8.de" <bp@...en8.de>, david.kaplan@....com
Subject: Re: [PATCH v11 0/8] KVM: SVM: Enable Secure TSC for SEV-SNP

On Wed, Aug 20, 2025, Nikunj A. Dadhania wrote:
> On 8/20/2025 4:55 PM, Huang, Kai wrote:
> > On Wed, 2025-08-20 at 14:18 +0530, Nikunj A. Dadhania wrote:
> >>>   - Continue on with snp_launch_start() if default_tsc_khz is '0'.  AFAICT,
> >>>     continuing on doesn't put the host at (any moer) risk. [Kai]
> >>
> >> If I hack default_tsc_khz  as '0', SNP guest kernel with SecureTSC spits out
> >> couple of warnings and finally panics:
> >>  
> > 
> > It's a surprise that the SEV_CMD_SNP_LAUNCH_START didn't fail in such
> > configuration. :-)
> 
> As mentioned here[1], this is an unsupported configuration as per the SNP
> Firmware ABI.

Yeah, but outside of AMD hardware/firmware, the usual response to an unsupported
configuration is to return an error :-D

Anyways, I'll fixup to the -EINVAL version from v10 when applying.