Re: PCI resource problems caused by improper address rounding

Robert Hancock
2007-12-19T00:11:38Z

Linus Torvalds wrote:
>
> On Tue, 18 Dec 2007, Richard Henderson wrote:
>> I've added dmesg, /proc/iomem, and lspci -v output to that bug.
>>
>> Basically, we have
>>
>> c0000000-cfffffff : free
>> ddf00000-dfefffff : PCI Bus #04
>> e0000000-efffffff : pnp 00:0b
>> f0000000-fedfffff : less than 256MB
>
> Gaah.
>
> That really is very unlucky. That 256M only goes at one point in the low
> 4GB, but the thing is, it fits perfectly well above it, and dammit, that
> resource is explicitly a 64-bit resource or a really good reason.
>
> However, I wonder about that
>
> e0000000-efffffff : pnp 00:0b
>
> thing. I actually suspect that that whole allocation is literally *meant*
> for that 256MB graphics aperture, but the kernel explicitly avoids it
> because it's listed in the PnP tables.

That is probably the MMCONFIG aperture, in that case any attempt to map
the graphics BAR there will have disastrous results. (This BIOS has an
MCFG table, though it looks like this Fedora kernel has MMCONFIG
disabled, so we can't tell what it actually contains.)

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