linux-kernel - Re: [PATCH] x86/cpufeatures: Force disable X86_FEATURE_ENQCMD and remove update

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Date:   Wed, 02 Jun 2021 12:20:18 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Fenghua Yu <fenghua.yu@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        x86 <x86@...nel.org>, iommu@...ts.linux-foundation.org,
        Ingo Molnar <mingo@...hat.com>, H Peter Anvin <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Christoph Hellwig <hch@...radead.org>,
        Peter Zijlstra <peterz@...radead.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Ashok Raj <ashok.raj@...el.com>,
        Jacob Jun Pan <jacob.jun.pan@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Sohil Mehta <sohil.mehta@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Vinod Koul <vkoul@...nel.org>, dmaengine@...r.kernel.org
Subject: Re: [PATCH] x86/cpufeatures: Force disable X86_FEATURE_ENQCMD and remove update_pasid()

On Wed, Jun 02 2021 at 12:14, Borislav Petkov wrote:

> On Sat, May 29, 2021 at 11:17:30AM +0200, Thomas Gleixner wrote:
>> --- a/arch/x86/include/asm/disabled-features.h
>> +++ b/arch/x86/include/asm/disabled-features.h
>> @@ -56,11 +56,8 @@
>>  # define DISABLE_PTI		(1 << (X86_FEATURE_PTI & 31))
>>  #endif
>>  
>> -#ifdef CONFIG_IOMMU_SUPPORT
>> -# define DISABLE_ENQCMD	0
>> -#else
>> -# define DISABLE_ENQCMD (1 << (X86_FEATURE_ENQCMD & 31))
>> -#endif
>> +/* Force disable because it's broken beyond repair */
>> +#define DISABLE_ENQCMD		(1 << (X86_FEATURE_ENQCMD & 31))
>
> Yeah, for that to work we need:
>
> ---
> From: Borislav Petkov <bp@...e.de>
> Date: Wed, 2 Jun 2021 12:07:52 +0200
> Subject: [PATCH] dmaengine: idxd: Use cpu_feature_enabled()
>
> When testing x86 feature bits, use cpu_feature_enabled() so that
> build-disabled features can remain off, regardless of what CPUID says.
>
> Fixes: 8e50d392652f ("dmaengine: idxd: Add shared workqueue support")
> Signed-off-by: Borislav Petkov <bp@...e.de>
> Cc: <stable@...r.kernel.org>

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>

Thanks for spotting this!

       tglx