linux-kernel - Re: [RFC v2 01/17] x86/apic: Add new driver for Secure AVIC

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Message-ID: <20250407131716.GCZ_PQXC9Gkc-LzS33@fat_crate.local>
Date: Mon, 7 Apr 2025 15:17:16 +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,
	kirill.shutemov@...ux.intel.com, huibo.wang@....com,
	naveen.rao@....com
Subject: Re: [RFC v2 01/17] x86/apic: Add new driver for Secure AVIC

On Wed, Apr 02, 2025 at 04:04:34PM +0530, Neeraj Upadhyay wrote:
> - snp_get_unsupported_features() looks like below.
>   It checks that, for the feature bits which are part of SNP_FEATURES_IMPL_REQ,
>   if they are enabled in hypervisor (and so reported in sev_status),
>   guest need to implement/enable those features. SAVIC also falls in that category
>   of SNP features.
> 
>   So, if CONFIG_AMD_SECURE_AVIC is disabled, guest would run with SAVIC feature
>   disabled in guest. This would cause undefined behavior for that guest if SAVIC
>   feature is active for that guest in hypervisor.

Ok, so SNP_FEATURES_IMPL_REQ will contain the SAVIC bit (unconditionally,
without the ifdeffery) and SNP_FEATURES_PRESENT will contain that thing you
had suggested with the ifdeffery to denote whether SAVIC support has been
enabled at build time:

https://lore.kernel.org/r/e0362a96-4b3a-44b1-8d54-806a6b045799@amd.com

or not.

Right?

-- 
Regards/Gruss,
    Boris.

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