Re: [Xen-ia64-devel] [PATCH][RFC][TAKE4] the P2M/VP patches

[Alex Williamson <alex.williamson@xxxxxx>]

On Mon, 2006-04-10 at 11:46 +0900, Isaku Yamahata wrote:
> > (XEN) mem40: type=11, attr=0x1, 
> > range=[0x0000080000000000-0x0000100000000000) (8388608MB)
> Plase note that type = 11 = EFI_MEMORY_MAPPED_IO
> 
> About 8TB (~= 8388608MB / 1024)  is required to map this range
> to dom0 for the P2M conversion table.
> This is the reason why the xenheap is used up.
> Allocating from domheap instead of xenheap doesn't solve because
> 8TB is too huge.
> 
> I didn't expect such a huge range.
> (BTW What is the MMIO range is used for?)

Hi Yamahata,

   This is a 64bit MMIO space.  Currently nothing really gets mapped
here, but if we're trying to map these like memory, we're in trouble.
As seen here, the range is huge, and it's not likely to get smaller in
the future.

> Perhaps you may see dom0 boot message by skipping to map the MMIO range.
> If dom0 tries to do access the MMIO range, something go wrong though.
> dom_fw_init()
>   =>efi_memmap_walk_type(EFI_MEMORY_MAPPED_IO,
>                          dom_fw_dom0_passthrough, &arg);
>     => dom_fw_dom0_passthrough() <<<<<<<<< modify this function.
> 
> 
> Maybe some special code for handling such a huge range is needed.

   Yes, for the short term we may be able to ignore this range, but we
need a solution fairly soon as it's possible firmware or dom0 might
choose to map cards into this MMIO space (this range is also descried in
ACPI for dom0).  Identity mapping of the entire uncached address space
for dom0 might be sufficient until we start on driver domains.  Thanks,

        Alex

-- 
Alex Williamson                             HP Linux & Open Source Lab


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