linux-kernel - Re: [PATCH] x86/resctrl: Fix to restore to original value when re-enabling hardware prefetch register

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Message-ID: <31b76df0-1b90-6494-57e7-fc9099c68e24@intel.com>
Date:   Tue, 24 May 2022 11:56:13 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Kohei Tarumizu <tarumizu.kohei@...itsu.com>,
        <fenghua.yu@...el.com>, <tglx@...utronix.de>, <mingo@...hat.com>,
        <bp@...en8.de>, <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
        <hpa@...or.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/resctrl: Fix to restore to original value when
 re-enabling hardware prefetch register

Hi Dave,

On 5/24/2022 11:41 AM, Dave Hansen wrote:
> On 5/17/22 21:55, Kohei Tarumizu wrote:
>> The current pseudo_lock.c code overwrites the value of the
>> MSR_MISC_FEATURE_CONTROL to 0 even if the original value is not 0.
>> Therefore, modify it to save and restore the original values.
>>
>> Fixes: 018961ae5579 ("x86/intel_rdt: Pseudo-lock region creation/removal core")
>> Fixes: 443810fe6160 ("x86/intel_rdt: Create debugfs files for pseudo-locking testing")
>> Fixes: 8a2fc0e1bc0c ("x86/intel_rdt: More precise L2 hit/miss measurements")
>> Signed-off-by: Kohei Tarumizu <tarumizu.kohei@...itsu.com>
> 
> Those commits are pretty old.  Is there any reason this is not stable@
> material?

While those commits are old the backport will not be trivial since some
lines affected did change since these original patches. I did not think it would
be worth the effort considering (1) the niche usages of this code, and (2) while these
patches can be found since v4.19 this code remains the only place in the kernel
that modifies this MSR (until the rest of Kohei's series lands). Apart from this
there is no particular reason why it cannot go to stable, we can surely make the
adjustments to make it palatable for v4.19.

Reinette