linux-kernel - Re: [PATCH v5 11/15] x86/mtrr: construct a memory map with cache modes

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Message-ID: <269cf003-3f96-727d-4a7c-72d52dba8854@suse.com>
Date:   Fri, 21 Apr 2023 16:35:02 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Michael Kelley <mikelley@...rosoft.com>
Subject: Re: [PATCH v5 11/15] x86/mtrr: construct a memory map with cache
 modes

On 21.04.23 13:23, Borislav Petkov wrote:
> On Thu, Apr 20, 2023 at 05:10:03PM +0200, Juergen Gross wrote:
>> I think this will need another final loop over the MTRRs to check against the
>> constructed map if a MTRR is completely useless.
> 
> Yeah, I slept on it: so I think there should be a patch ontop which does
> add debug output - disabled by default and controllable by adding
> "mtrr=debug" on the cmdline or so - which dumps the cache map operations
> (add/remove) and the final table.

Okay.

> The reason being, when this cache_map thing hits upstream, we would need
> a way to debug any potential issues which people might report so asking
> them to do a "mtrr=debug" boot would be a good help.
> 
> And pls make the prints pr_info() and not pr_debug() because people
> should not have to recompile in order to enable that.

Agreed.

>> Another question: in case we detect such a hidden MTRR, should it be disabled
>> in order to have more MTRRs available for run-time adding?
> 
> Let's not do anything for now and address this if really needed.

Okay.


Juergen

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