linux-kernel - Re: [PATCH] x86/sev: Guard sev_evict_cache() with CONFIG_AMD_MEM

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Message-ID: <20250912204929.pls6245t746gtalr@amd.com>
Date: Fri, 12 Sep 2025 15:49:29 -0500
From: Michael Roth <michael.roth@....com>
To: Borislav Petkov <bp@...en8.de>
CC: Tom Lendacky <thomas.lendacky@....com>, <linux-kernel@...r.kernel.org>,
	<x86@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar
	<mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>, "Sean
 Christopherson" <seanjc@...gle.com>, <stable@...nel.org>
Subject: Re: [PATCH] x86/sev: Guard sev_evict_cache() with
 CONFIG_AMD_MEM_ENCRYPT

On Fri, Sep 12, 2025 at 10:42:03PM +0200, Borislav Petkov wrote:
> On Fri, Sep 12, 2025 at 03:29:19PM -0500, Tom Lendacky wrote:
> > The sev_evict_cache() is guest-related code and should be guarded by
> > CONFIG_AMD_MEM_ENCRYPT, not CONFIG_KVM_AMD_SEV. Move the function
> > declarations under the appropriate #ifdef.
> > 
> > Fixes: 7b306dfa326f ("x86/sev: Evict cache lines during SNP memory validation")
> > Cc: <stable@...nel.org>
> 
> Do we really want this in stable?
> 
> I haven't seen any breakages from it...

I think that's actually the concerning thing. If someone built a guest
kernel with CONFIG_KVM_AMD_SEV=y they might be under the impression that
this is performing evictions when it's actually just a stub function.

-Mike

> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette