linux-kernel - Re: [PATCH v11 04/13] x86/cpufeatures: Add Bandwidth Monitoring Event Configuration feature flag

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Message-ID: <Y8/Bx7chrl1DC4Az@zn.tnic>
Date:   Tue, 24 Jan 2023 12:32:23 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Reinette Chatre <reinette.chatre@...el.com>
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Subject: Re: [PATCH v11 04/13] x86/cpufeatures: Add Bandwidth Monitoring
 Event Configuration feature flag

On Mon, Jan 09, 2023 at 03:43:11PM -0800, Reinette Chatre wrote:
> We could make a rule that no more resctrl related features are added to
> cpuinfo but I am hesitant to remove the ones that are already there.

Yes, that makes sense.

And note that we try for /proc/cpuinfo to contain flags where the kernel has
received (substantial) enablement work to support a feature. Shadow stack would
be one good example.

If resctrl needs to use a feature and it cannot use that feature without kernel
enablement, then yes, by all means, it should use /proc/cpuinfo and not the
corresponding CPUID bit. Because the presence of the flag in /proc/cpuinfo says
"yes, you can use the feature and the kernel you're running on has the required
support."

Thx.

-- 
Regards/Gruss,
    Boris.

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