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

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Message-ID: <YLdZ7bZDPNup1n9c@zn.tnic>
Date:   Wed, 2 Jun 2021 12:14:05 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Thomas Gleixner <tglx@...utronix.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 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>
---
 drivers/dma/idxd/init.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/dma/idxd/init.c b/drivers/dma/idxd/init.c
index 2a926bef87f2..776fd44aff5f 100644
--- a/drivers/dma/idxd/init.c
+++ b/drivers/dma/idxd/init.c
@@ -745,12 +745,12 @@ static int __init idxd_init_module(void)
 	 * If the CPU does not support MOVDIR64B or ENQCMDS, there's no point in
 	 * enumerating the device. We can not utilize it.
 	 */
-	if (!boot_cpu_has(X86_FEATURE_MOVDIR64B)) {
+	if (!cpu_feature_enabled(X86_FEATURE_MOVDIR64B)) {
 		pr_warn("idxd driver failed to load without MOVDIR64B.\n");
 		return -ENODEV;
 	}
 
-	if (!boot_cpu_has(X86_FEATURE_ENQCMD))
+	if (!cpu_feature_enabled(X86_FEATURE_ENQCMD))
 		pr_warn("Platform does not have ENQCMD(S) support.\n");
 	else
 		support_enqcmd = true;
-- 
2.29.2

For the newly CCed parties, pls check

https://lkml.kernel.org/r/87mtsd6gr9.ffs@nanos.tec.linutronix.de

for more info.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette