linux-kernel - Re: [PATCH v2 0/4] x86, fpu/kvm: fix crash with AMX

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Message-ID: <20260115122204.GDaWjb7Npp80GK-mFn@fat_crate.local>
Date: Thu, 15 Jan 2026 13:22:04 +0100
From: Borislav Petkov <bp@...en8.de>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org, seanjc@...gle.com,
	x86@...nel.org
Subject: Re: [PATCH v2 0/4] x86, fpu/kvm: fix crash with AMX

On Thu, Jan 01, 2026 at 10:05:12AM +0100, Paolo Bonzini wrote:
> Fix a possible host panic, due to an unexpected #NM, when a KVM guest
> is using AMX features.
> 
> The guest's XFD value, which is stored in fpstate->xfd, is used for both
> guest execution and host XSAVE operations. 

This already sounds weird. Why?

Why don't we carry separate XFD copies - guest and host - which we use for the
guest and the host, respectively?

-- 
Regards/Gruss,
    Boris.

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