linux-kernel - Re: [PATCH v8 0/6] Introduce CET supervisor state support

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Message-ID: <f575567b-0d1f-4631-ad48-1ef5aaca1f75@intel.com>
Date: Fri, 23 May 2025 10:12:22 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Sean Christopherson <seanjc@...gle.com>, Chao Gao <chao.gao@...el.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
 tglx@...utronix.de, pbonzini@...hat.com, peterz@...radead.org,
 rick.p.edgecombe@...el.com, weijiang.yang@...el.com, john.allen@....com,
 bp@...en8.de, chang.seok.bae@...el.com, xin3.li@...el.com,
 Dave Hansen <dave.hansen@...ux.intel.com>, Eric Biggers
 <ebiggers@...gle.com>, "H. Peter Anvin" <hpa@...or.com>,
 Ingo Molnar <mingo@...hat.com>, Kees Cook <kees@...nel.org>,
 Maxim Levitsky <mlevitsk@...hat.com>, Mitchell Levy
 <levymitchell0@...il.com>, Nikolay Borisov <nik.borisov@...e.com>,
 Oleg Nesterov <oleg@...hat.com>, Sohil Mehta <sohil.mehta@...el.com>,
 Stanislav Spassov <stanspas@...zon.de>,
 Vignesh Balasubramanian <vigbalas@....com>
Subject: Re: [PATCH v8 0/6] Introduce CET supervisor state support

On 5/23/25 09:57, Sean Christopherson wrote:
> Side topic, and *probably* unrelated to this series, I tripped the following
> WARN when running it through the KVM tests (though I don't think it has anything
> to do with KVM?).  The WARN is the version of xfd_validate_state() that's guarded
> by CONFIG_X86_DEBUG_FPU=y.
> 
>    WARNING: CPU: 232 PID: 15391 at arch/x86/kernel/fpu/xstate.c:1543 xfd_validate_state+0x65/0x70

Huh, and the two processes getting hit by it:

   CPU: 232 UID: 0 PID: 15391 Comm: DefaultEventMan ...
   CPU: 77  UID: 0 PID: 14821 Comm: futex-default-S ...

don't _look_ like KVM test processes. My guess would be it's some
mixture of KVM and a signal handler fighting with XFD state.

I take it this is a Sapphire Rapids system? Is there anything
interesting about the config other than CONFIG_X86_DEBUG_FPU?