Public bug reported:
The kernel's Documentation/x86/mtrr.txt
or Documentation/mtrr.txt
describes the ioctl interface to the MTRRs.
The sample code for printing out the MTRRs ("mtrr-show.c") fails to
print many of the values. I think that this is a bug in the ioctl
implementation, not the documentation since the same code works on
Fedora 9.
/proc/mttr shows:
reg00: base=0xd0000000 (3328MB), size= 256MB: uncachable, count=1
reg01: base=0xe0000000 (3584MB), size= 512MB: uncachable, count=1
reg02: base=0x00000000 ( 0MB), size=4096MB: write-back, count=1
reg03: base=0x100000000 (4096MB), size=2048MB: write-back, count=1
reg04: base=0x180000000 (6144MB), size= 512MB: write-back, count=1
reg05: base=0x1a0000000 (6656MB), size= 256MB: write-back, count=1
The sample code prints:
Register: 0 base: 0xd0000000 size: 0x10000000 type: uncachable
Register: 1 base: 0xe0000000 size: 0x20000000 type: uncachable
Register: 2 disabled
Register: 3 disabled
Register: 4 disabled
Register: 5 disabled
Register: 6 disabled
Register: 7 disabled
If I remove the disabled check, it prints:
Register: 0 base: 0xd0000000 size: 0x10000000 type: uncachable
Register: 1 base: 0xe0000000 size: 0x20000000 type: uncachable
Register: 2 base: 0x0 size: 0x0 type: uncachable
Register: 3 base: 0x0 size: 0x0 type: uncachable
Register: 4 base: 0x0 size: 0x0 type: uncachable
Register: 5 base: 0x0 size: 0x0 type: uncachable
Register: 6 base: 0x0 size: 0x0 type: uncachable
Register: 7 base: 0x0 size: 0x0 type: uncachable
Note: the architecture is AMD64. The code is native (according to
file(1)).
The same code seems to work on a Fedora 9 x86-64 system, albeit one with
less than 4G of RAM.
BTW, the reason I care is that the MTRRs need to be rearranged for X to
work on my system and I want to do that programmatically.
** Affects: linux-meta (Ubuntu)
Importance: Undecided
Status: New
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MTRR ioctls don't work as documented
https://bugs.launchpad.net/bugs/253204
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