linux-kernel - Re: [PATCH v3 6/9] x86: resctrl: pseudo_lock: Fix to restore to original value when re-enabling hardware prefetch register

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Message-ID: <2eb705cd-8607-4b8c-2c0b-31265d503eed@intel.com>
Date:   Wed, 20 Apr 2022 13:56:07 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Kohei Tarumizu <tarumizu.kohei@...itsu.com>,
        catalin.marinas@....com, will@...nel.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        fenghua.yu@...el.com, reinette.chatre@...el.com
Subject: Re: [PATCH v3 6/9] x86: resctrl: pseudo_lock: Fix to restore to
 original value when re-enabling hardware prefetch register

On 4/19/22 20:02, Kohei Tarumizu wrote:
> The current pseudo_lock.c code overwrittes 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.

It would be nice to mention that the wrmsr()'s in this patch are only
done inside of an interrupt-disabled region.  Without that little tidbit
of information, it's not obviously correct that the smp_call_function()
in patch 8/9 is correct.

The x86 code here looks reasonable otherwise.  It's a little bit of a
shame that this is *ONLY* for BROADWELL_X for now, but I assume you were
just conservative about it because that's all you have to test on.