linux-kernel - Re: [RFC 01/14] x86/apic: Add new driver for Secure AVIC

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Message-ID: <20241009052336.GAZwYTWDLWfSPtZe5b@fat_crate.local>
Date: Wed, 9 Oct 2024 07:23:36 +0200
From: Borislav Petkov <bp@...en8.de>
To: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
Cc: linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
	dave.hansen@...ux.intel.com, Thomas.Lendacky@....com,
	nikunj@....com, Santosh.Shukla@....com, Vasant.Hegde@....com,
	Suravee.Suthikulpanit@....com, David.Kaplan@....com, x86@...nel.org,
	hpa@...or.com, peterz@...radead.org, seanjc@...gle.com,
	pbonzini@...hat.com, kvm@...r.kernel.org
Subject: Re: [RFC 01/14] x86/apic: Add new driver for Secure AVIC

On Wed, Oct 09, 2024 at 07:26:55AM +0530, Neeraj Upadhyay wrote:
> As SECURE_AVIC feature is not supported (as reported by snp_get_unsupported_features())
> by guest at this patch in the series, it is added to SNP_FEATURES_IMPL_REQ here. The bit
> value within SNP_FEATURES_IMPL_REQ hasn't changed with this change as the same bit pos
> was part of MSR_AMD64_SNP_RESERVED_MASK before this patch. In patch 14 SECURE_AVIC guest
> support is indicated by guest.

So what's the point of adding it to SNP_FEATURES_IMPL_REQ here? What does that
do at all in this patch alone? Why is this change needed in here?

IOW, why don't you do all the feature bit handling in the last patch, where it
all belongs logically?

In the last patch you can start *testing* for
MSR_AMD64_SNP_SECURE_AVIC_ENABLED *and* enforce it with SNP_FEATURES_PRESENT.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette