linux-kernel - Re: [PATCH v2 01/10] x86/mtrr: fix MTRR fixup on APs

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Date:   Mon, 22 Aug 2022 10:32:28 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     xen-devel@...ts.xenproject.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, stable@...r.kernel.org
Subject: Re: [PATCH v2 01/10] x86/mtrr: fix MTRR fixup on APs

On 22.08.22 10:28, Borislav Petkov wrote:
> On Mon, Aug 22, 2022 at 07:17:40AM +0200, Juergen Gross wrote:
>> And then there is mtrr_state_warn() in arch/x86/kernel/cpu/mtrr/generic.c
>> which has a comment saying:
>>
>> /* Some BIOS's are messed up and don't set all MTRRs the same! */
> 
> That thing also says:
> 
>          pr_info("mtrr: probably your BIOS does not setup all CPUs.\n");
>          pr_info("mtrr: corrected configuration.\n");
> 
> because it'll go and force on all CPUs the MTRR state it read from the
> BSP in mtrr_bp_init->get_mtrr_state.
> 
>> Yes, the chances are slim to hit such a box,
> 
> Well, my workstation says:
> 
> $ dmesg | grep -i mtrr
> [    0.391514] mtrr: your CPUs had inconsistent variable MTRR settings
> [    0.395199] mtrr: probably your BIOS does not setup all CPUs.
> [    0.399199] mtrr: corrected configuration.
> 
> but that's the variable MTRRs.
> 
>> but your reasoning suggests I should remove the related code?
> 
> My reasoning says you should not do anything at all here - works as
> advertized. :-)
> 

And what about the:

   pr_warn("mtrr: your CPUs had inconsistent MTRRdefType settings\n");

This is the case the patch would fix.


Juergen

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