Re: [PATCH v6 00/16] x86/mtrr: fix handling with PAT but without MTRR

Juergen Gross
2023-05-31T09:32:38Z

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On 31.05.23 10:35, Borislav Petkov wrote:
> On Wed, May 31, 2023 at 09:28:57AM +0200, Juergen Gross wrote:
>> Can you please boot the system with the MTRR patches and specify "mtrr=debug"
>> on the command line? I'd be interested in the raw register values being read
>> and the resulting memory type map.
>
> This is exactly why I wanted this option. And you're already putting it
> to good use. :-P
>
> Full dmesg below.
>
> [ 0.012878] last_pfn = 0x450000 max_arch_pfn = 0x400000000
> [ 0.018357] MTRR default type: uncachable
> [ 0.022347] MTRR fixed ranges enabled:
> [ 0.026085] 00000-9FFFF write-back
> [ 0.029650] A0000-BFFFF uncachable
> [ 0.033214] C0000-FFFFF write-protect
> [ 0.037039] MTRR variable ranges enabled:
> [ 0.041038] 0 base 000000000000000 mask 0003FFC00000000 write-back

16 GB WB at address 0.

> [ 0.047383] 1 base 000000400000000 mask 0003FFFC0000000 write-back

1 GB WB at address 16GB.

> [ 0.053730] 2 base 000000440000000 mask 0003FFFF0000000 write-back

256MB WB at address 17GB.

This means per default 0-44fffffff are WB.

> [ 0.060076] 3 base 0000000AE000000 mask 0003FFFFE000000 uncachable

32MB UC at AE000000

> [ 0.066421] 4 base 0000000B0000000 mask 0003FFFF0000000 uncachable

256MB UC at B0000000

> [ 0.072768] 5 base 0000000C0000000 mask 0003FFFC0000000 uncachable

512MB UC at C0000000

So an UC hole at AE000000-FFFFFFFF.

> [ 0.079114] 6 disabled
> [ 0.081635] 7 disabled
> [ 0.084156] 8 disabled
> [ 0.086677] 9 disabled
> [ 0.089203] total RAM covered: 16352M
> [ 0.093023] Found optimal setting for mtrr clean up

It seems as if mtrr_cleanup() did change the MTRR settings.

What it did would have been printed if pr_debug() would have been
active. :-(

> [ 0.097734] gran_size: 64K chunk_size: 64M num_reg: 8 lose cover RAM: 0G
> [ 0.104864] MTRR map: 6 entries (3 fixed + 3 variable; max 23), built from 10 variable MTRRs
> [ 0.113294] 0: 0000000000000000-000000000009ffff write-back
> [ 0.119033] 1: 00000000000a0000-00000000000bffff uncachable
> [ 0.124771] 2: 00000000000c0000-00000000000fffff write-protect
> [ 0.130769] 3: 0000000000100000-00000000adffffff write-back
> [ 0.136508] 4: 00000000ae000000-00000000afffffff uncachable
> [ 0.142246] 5: 0000000100000000-000000044fffffff write-back

The MTRR map seems to be fine assuming the MTRR values before the "clean up".

> [ 0.147992] x86/PAT: Configuration [0-7]: WB WC UC- UC WB WP UC- WT
> [ 0.155122] e820: update [mem 0xae000000-0xafffffff] usable ==> reserved
> [ 0.161663] e820: update [mem 0xc0000000-0xffffffff] usable ==> reserved
> [ 0.168358] e820: update [mem 0x110000000-0x1ffffffff] usable ==> reserved
> [ 0.175227] WARNING: BIOS bug: CPU MTRRs don't cover all of memory, losing
3840MB of RAM.

Clean up messed with the settings, resulting in loss of RAM.

Did you check whether CONFIG_MTRR_SANITIZER_ENABLE_DEFAULT was the same in both
kernels you've tested?

Juergen

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