linux-kernel - Re: [PATCH v4 09/12] x86/mtrr: construct a memory map with cache modes

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Message-ID: <2703abe4-f164-2208-99ac-0935ebd41716@suse.com>
Date:   Mon, 3 Apr 2023 08:57:48 +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>
Subject: Re: [PATCH v4 09/12] x86/mtrr: construct a memory map with cache
 modes

On 01.04.23 16:24, Borislav Petkov wrote:
> On Fri, Mar 31, 2023 at 03:23:13PM +0200, Juergen Gross wrote:
>> In general the critical case is add_map_entry_at() returning 2 (in the
>> case it is returning 1, the index can be set to -1, but there is always
>> the "continue" statement right after that, which would execute the "i++"
>> of the "for" statement).
>>
>> add_map_entry_at() can return 2 only, if it detects "merge_prev" and
>> "merge_next". "merge_prev" can be set only if the current index was > 0,
>> which makes it impossible to return 2 if the index was 0.
> 
> Yeah, in the meantime I did add some debug printks in order to find my
> way around that code...
> 
>> How should it be named? AMD TOP_MEM2 MSR?
> 
> It is already called that way - see "git grep TOP_MEM2" output.
> 
>> The problem isn't an added MTRR register, but a possibly replaced or removed
>> one. Handling that is much more complicated, so I've chosen to do it the simple
>> way.
> 
> Pls put that blurb over the function: needs to be called when MTRRs get
> modified so that the map is kept valid, yadda yadda...

Okay.


Juergen

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