Re: [Xen-devel] c/s 19576 vs. AMD systems

[Frank Arnold <frank.arnold@xxxxxxx>]

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@xxxxxxx>
System Design Technician, Software Test
AMD Operating System Research Center
Dresden, Germany
Tel: +49 351 448 356702


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