linux-kernel - Re: [PATCH v3.1 10/12] x86/mtrr: use new cache_map in mtrr_type

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Date:   Mon, 27 Feb 2023 08:11:06 +0100
From:   Juergen Gross <jgross@...e.com>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v3.1 10/12] x86/mtrr: use new cache_map in
 mtrr_type_lookup()

On 26.02.23 18:00, Michael Kelley (LINUX) wrote:
> From: Juergen Gross <jgross@...e.com> Sent: Thursday, February 23, 2023 10:37 PM
>>
>> Instead of crawling through the MTRR register state, use the new
>> cache_map for looking up the cache type(s) of a memory region.
>>
>> This allows now to set the uniform parameter according to the
>> uniformity of the cache mode of the region, instead of setting it
>> only if the complete region is mapped by a single MTRR. This now
>> includes even the region covered by the fixed MTRR registers.
>>
>> Make sure uniform is always set.
>>
>> Signed-off-by: Juergen Gross <jgross@...e.com>
>> ---
>> V3:
>> - new patch
>> V3.1:
>> - fix type_merge() (Michael Kelley)
> 
> Thanks.  This version fixes the problem I previously reported with a normal
> VM.
> 
> However, I'm seeing a different problem in a Confidential VM where
> mtrr_overwrite_state() is used.  In this case, we have no MTRRs, and when
> mtrr_copy_map() is called, the copy is not done, and cache_map is set
> to NULL.  Subsequently when mtrr_type_lookup() is called, the check
> for a NULL cache_map causes MTRR_TYPE_UNCACHABLE to be returned.
> Then we're back to the original problem where pat_x_mtrr_type()
> returns UC- instead of WB.

Sigh. Just removing the test for cache_map being NULL in mtrr_type_lookup()
should do the job.

Will send V4 soon.


Juergen

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