Re: c/s 19576 vs. AMD systems

["Jan Beulich" <jbeulich@novell.com>]

Keir,

these log fragments point out another issue: Only RAM regions should be
removed, but all other regions should remain. This is not the least because
Linux checks the E820 table to have e.g. the MCFG area covered as
reserved.

Jan

>>> Frank Arnold <frank.arnold@amd.com> 29.04.09 19:23 >>>
Am Mittwoch, den 29.04.2009, 09:53 +0100 schrieb Jan Beulich:
> Keir,
> 
> I'm afraid this change is going to hurt on AMD systems where memory extends
> beyond the 4Gb boundary: Both such systems that I have direct access to
> have their Intel MTRRs only defined up to the 4Gb boundary, yet through
> the use of AMD specific MSRs (SYS_CFG.Tom2ForceMemTypeWB and TOM2)
> the default memory type for everything beyond the 4Gb boundary is WB.
> On these systems there shouldn't be any clipping. I certainly can put together
> a patch for this, but it'll take me a couple of days until I'd get to it.

We can confirm this to be a very real issue. At least on 4 of our test
boxes the memory gets truncated after these changes.

One example:
Mainboard: ASUSTeK Computer INC. M2N-MX SE Plus
CPU:       AMD Athlon(tm) 64 X2 Dual Core Processor 5000+
           Family: 15, Model: 107, Stepping: 1
BIOS Information:
           Vendor: American Megatrends Inc.
           Version: 0302
           Release Date: 12/04/2007
Memory:    4 GB


With changeset 19575:dc5bd14a4675:
# xm info
...
total_memory           : 3967
...
# xm dmesg
...
(XEN) Xen-e820 RAM map:
(XEN)  0000000000000000 - 000000000009fc00 (usable)
(XEN)  000000000009fc00 - 00000000000a0000 (reserved)
(XEN)  00000000000e4000 - 0000000000100000 (reserved)
(XEN)  0000000000100000 - 00000000b7fb0000 (usable)
(XEN)  00000000b7fb0000 - 00000000b7fbe000 (ACPI data)
(XEN)  00000000b7fbe000 - 00000000b7fe0000 (ACPI NVS)
(XEN)  00000000b7fe0000 - 00000000b7fee000 (reserved)
(XEN)  00000000b7ff0000 - 00000000b8000000 (reserved)
(XEN)  00000000fec00000 - 00000000fec01000 (reserved)
(XEN)  00000000fee00000 - 00000000fef00000 (reserved)
(XEN)  00000000fff00000 - 0000000100000000 (reserved)
(XEN)  0000000100000000 - 0000000140000000 (usable)
(XEN) System RAM: 3967MB (4062524kB)
...


Same box with changeset 19582:648d7de355dd:
# xm info
...
total_memory           : 2943
...
# xm dmesg
...
(XEN) WARNING: MTRRs do not cover all of memory.
(XEN) Truncating memory map to 3145728kB
(XEN) Xen-e820 RAM map:
(XEN)  0000000000000000 - 000000000009fc00 (usable)
(XEN)  000000000009fc00 - 00000000000a0000 (reserved)
(XEN)  00000000000e4000 - 0000000000100000 (reserved)
(XEN)  0000000000100000 - 00000000b7fb0000 (usable)
(XEN)  00000000b7fb0000 - 00000000b7fbe000 (ACPI data)
(XEN)  00000000b7fbe000 - 00000000b7fe0000 (ACPI NVS)
(XEN)  00000000b7fe0000 - 00000000b7fee000 (reserved)
(XEN)  00000000b7ff0000 - 00000000b8000000 (reserved)
(XEN) System RAM: 2943MB (3013948kB)
...


-- 
Frank Arnold <frank.arnold@amd.com>
System Design Technician, Software Test
AMD Operating System Research Center
Dresden, Germany
Tel: +49 351 448 356702


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