linux-kernel - Re: [PATCH 2/2] KVM: x86: Harden KVM against imbalanced load/put of guest FPU state

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Message-ID: <aQmYF8jDKlzecQ6A@intel.com>
Date: Tue, 4 Nov 2025 14:07:19 +0800
From: Chao Gao <chao.gao@...el.com>
To: Sean Christopherson <seanjc@...gle.com>
CC: Paolo Bonzini <pbonzini@...hat.com>, <kvm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Alexander Potapenko <glider@...gle.com>
Subject: Re: [PATCH 2/2] KVM: x86: Harden KVM against imbalanced load/put of
 guest FPU state

On Thu, Oct 30, 2025 at 11:58:02AM -0700, Sean Christopherson wrote:
>Assert, via KVM_BUG_ON(), that guest FPU state isn't/is in use when
>loading/putting the FPU to help detect KVM bugs without needing an assist
>from KASAN.  If an imbalanced load/put is detected, skip the redundant
>load/put to avoid clobbering guest state and/or crashing the host.
>
>Note, kvm_access_xstate_msr() already provides a similar assertion.
>
>Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Chao Gao <chao.gao@...el.com>