Re: Are these MTRR settings correct?

[Robert Hancock <hancockrwd@gmail.com>]

On 12/13/2009 03:25 AM, Yinghai Lu wrote:
> On Sun, Dec 13, 2009 at 12:26 AM, Tvrtko Ursulin<tvrtko@ursulin.net>  wrote:
>> On Sunday 13 Dec 2009 08:07:44 Tvrtko Ursulin wrote:
>>> Hi all,
>>>
>>> They look a bit suspicious to me since machine has 4GB of RAM, and range
>>>   covered by MTRR seems to be short of that. Last entry is from the IGP I
>>>   believe, which is also strange because in BIOS an option to map that above
>>>   4G is set.
>>>
>>> tvrtko@deuteros:~>  cat /proc/mtrr
>>> reg00: base=0x000000000 (    0MB), size= 2048MB, count=1: write-back
>>> reg01: base=0x080000000 ( 2048MB), size= 1024MB, count=1: write-back
>>> reg02: base=0x0c0000000 ( 3072MB), size=  256MB, count=1: write-back
>>> reg03: base=0x0d0000000 ( 3328MB), size=  256MB, count=1: write-combining
>>
>> This IGP has a sideport memory, above sideport plus UMA was enabled in BIOS. If I limit it to
>> only 128Mb of sideport framebuffer then it looks like this:
>>
>> reg00: base=0x000000000 (    0MB), size= 2048MB, count=1: write-back
>> reg01: base=0x080000000 ( 2048MB), size= 1024MB, count=1: write-back
>> reg02: base=0x0c0000000 ( 3072MB), size=  256MB, count=1: write-back
>> reg03: base=0x0f0000000 ( 3840MB), size=  128MB, count=1: write-combining
>>
>> Still looks like from 3328MB to 3840MB is of status unknown?

No covering entry means that area is uncacheable. (In most cases - as 
Yinghai mentioned some AMD CPUs special-case any memory above 4GB as 
write-back without needing an MTRR entry.)

>>
>> dmesg in that case:
>>
>> [    0.000000] Linux version 2.6.32 (tvrtko@deuteros) (gcc version 4.4.1 [gcc-4_4-branch revision 150839] (SUSE Linux) ) #2 SMP PREEMPT Sat
>> Dec 12 20:44:59 GMT 2009
>> [    0.000000] Command line: root=UUID="78df20fb-791f-4a82-b1d6-4e043aa663d1" resume=UUID="fc2d8cd0-fed3-4196-b346-83de887dfcf7"
>> splash=silent quiet vga=0x31a 3
>> [    0.000000] KERNEL supported cpus:
>> [    0.000000]   Intel GenuineIntel
>> [    0.000000]   AMD AuthenticAMD
>> [    0.000000]   Centaur CentaurHauls
>> [    0.000000] BIOS-provided physical RAM map:
>> [    0.000000]  BIOS-e820: 0000000000000000 - 000000000009ec00 (usable)
>> [    0.000000]  BIOS-e820: 000000000009ec00 - 00000000000a0000 (reserved)
>> [    0.000000]  BIOS-e820: 00000000000e4000 - 0000000000100000 (reserved)
>> [    0.000000]  BIOS-e820: 0000000000100000 - 00000000cff90000 (usable)
>> [    0.000000]  BIOS-e820: 00000000cff90000 - 00000000cffa8000 (ACPI data)
>> [    0.000000]  BIOS-e820: 00000000cffa8000 - 00000000cffd0000 (ACPI NVS)
>> [    0.000000]  BIOS-e820: 00000000cffd0000 - 00000000d0000000 (reserved)
>> [    0.000000]  BIOS-e820: 00000000ff700000 - 0000000100000000 (reserved)
>> [    0.000000]  BIOS-e820: 0000000100000000 - 0000000130000000 (usable)
>> [    0.000000] DMI present.
>> [    0.000000] AMI BIOS detected: BIOS may corrupt low RAM, working around it.
>> [    0.000000] e820 update range: 0000000000000000 - 0000000000010000 (usable) ==>  (reserved)
>> [    0.000000] last_pfn = 0x130000 max_arch_pfn = 0x400000000
>> [    0.000000] MTRR default type: uncachable
>> [    0.000000] MTRR fixed ranges enabled:
>> [    0.000000]   00000-9FFFF write-back
>> [    0.000000]   A0000-EFFFF uncachable
>> [    0.000000]   F0000-FFFFF write-protect
>> [    0.000000] MTRR variable ranges enabled:
>> [    0.000000]   0 base 000000000000 mask FFFF80000000 write-back
>> [    0.000000]   1 base 000080000000 mask FFFFC0000000 write-back
>> [    0.000000]   2 base 0000C0000000 mask FFFFF0000000 write-back
>> [    0.000000]   3 disabled
>> [    0.000000]   4 disabled
>> [    0.000000]   5 disabled
>> [    0.000000]   6 disabled
>> [    0.000000]   7 disabled
>> [    0.000000] TOM2: 0000000130000000 aka 4864M
>
> that [d0000000, e0000000) is to mmio space.
>
> your var mtrrs is covering [0, d0000000)
>
> and AMD K8 Rev F, will auto cover your [4G, TOM2) aka [4G, 4G+3*256M) to WB ...
> ...
>
>> [    0.251043] node 0 link 0: io port [1000, ffffff]
>> [    0.251045] TOM: 00000000d0000000 aka 3328M
>> [    0.251046] Fam 10h mmconf [e0000000, efffffff]
>> [    0.251048] node 0 link 0: mmio [a0000, bffff]
>> [    0.251050] node 0 link 0: mmio [d0000000, dfffffff]
>> [    0.251051] node 0 link 0: mmio [e0000000, efffffff] ==>  none
>> [    0.251053] node 0 link 0: mmio [f0000000, fe7fffff]
>> [    0.251055] node 0 link 0: mmio [fe800000, fe9fffff]
>> [    0.251056] node 0 link 0: mmio [fea00000, ffefffff]
>> [    0.251058] TOM2: 0000000130000000 aka 4864M
>> [    0.251059] bus: [00,07] on node 0 link 0
>> [    0.251060] bus: 00 index 0 io port: [0, ffff]
>> [    0.251062] bus: 00 index 1 mmio: [a0000, bffff]
>> [    0.251063] bus: 00 index 2 mmio: [d0000000, dfffffff]
>> [    0.251064] bus: 00 index 3 mmio: [f0000000, ffffffff]
>> [    0.251065] bus: 00 index 4 mmio: [130000000, fcffffffff]
>> [    0.251072] ACPI: bus type pci registered
>> [    0.251107] PCI: MCFG configuration 0: base e0000000 segment 0 buses 0 - 255
>> [    0.251109] PCI: Not using MMCONFIG.
>> [    0.251110] PCI: Using configuration type 1 for base access
>> [    0.251111] PCI: Using configuration type 1 for extended access
>
> only concern that is your BIOS doesn't have [e000000, F0000000)
> reserved in e820 or acpi etc.

If you look later after in dmesg it is reserved in ACPI so it does use 
it after all. (This is a bit confusing in these cases, because it says 
"not using MMCONFIG" and then decides to use it a few lines later. Maybe 
it should say "skipping early MMCONFIG enable" or something instead.)

>
> you could try to use "pci=check_enable_amd_mmconf" in boot command
> line to enable it.
>
> YH