Re: [Xen-devel] [PATCH] Enable K8 GART as an IOMMU

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 13/2/07 23:19, "Langsdorf, Mark" <mark.langsdorf@xxxxxxx> wrote:

>>> /* Protected by balloon_lock. */
>>> -#define MAX_CONTIG_ORDER 9 /* 2MB */
>>> +#define MAX_CONTIG_ORDER 16 /* 256MB */
>>> static unsigned long discontig_frames[1<<MAX_CONTIG_ORDER];
>>> static multicall_entry_t cr_mcl[1<<MAX_CONTIG_ORDER];
>> 
>> This seems dangerous to me.
> 
> We need at least 64MB of contiguous memory for the aperture.

Not that I know anything much about the K8 GART, but I assume the aperture
is an address range that the GART takes control of and dynamically aliases
other RAM pages into? Is it necessary to burn 64MB of RAM (which is
presumably inaccessible when the GART is turned on)? Will the BIOS not
already have conveniently piointed the aperture into a RAM hole (e.g., just
below 4GB)?

 -- Keir



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