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

From: Juergen Gross
Date: Mon Aug 22 2022 - 04:32:35 EST


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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