linux-kernel - Re: [PATCH v2 10/11] tools/objtool: Check for use of the ENQCMD instruction in the kernel

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Message-ID: <20211217225706.32ahbyf5yeuzrhre@treble>
Date:   Fri, 17 Dec 2021 14:57:06 -0800
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Fenghua Yu <fenghua.yu@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        iommu@...ts.linux-foundation.org, x86 <x86@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 10/11] tools/objtool: Check for use of the ENQCMD
 instruction in the kernel

On Fri, Dec 17, 2021 at 10:01:35PM +0000, Fenghua Yu wrote:
> The ENQCMD implicitly accesses the PASID_MSR to fill in the pasid field
> of the descriptor being submitted to an accelerator. But there is no
> precise (and stable across kernel changes) point at which the PASID_MSR
> is updated from the value for one task to the next.
> 
> Kernel code that uses accelerators must always use the ENQCMDS instruction
> which does not access the PASID_MSR.
> 
> Check for use of the ENQCMD instruction in the kernel and warn on its
> usage.
> 
> Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> Reviewed-by: Tony Luck <tony.luck@...el.com>
> ---
> v2:
> - Simplify handling ENQCMD (PeterZ and Josh)

Acked-by: Josh Poimboeuf <jpoimboe@...hat.com>

-- 
Josh