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SubjectRe: [Pkg-xen-devel] ioatdma: Boot process hangs then reboots when using Xen + Linux 3.2
On Tue, 2012-03-06 at 06:14 -0800, Dan Williams wrote:
> [ 9.276817] ioatdma 0000:00:16.4: desc[0]:
> (0x300cc7000->0x300cc7040) cookie: 0 flags: 0x2 ctl: 0x29 (op: 0
> int_en: 1 compl: 1)
> ...
> [ 9.276832] ioatdma 0000:00:16.4: ioat_get_current_completion:
> phys_complete: 0xcc7000
> Thanks, this clearly shows that our descriptors are above 4GB and that
> the driver truncates the completion word.
> Is this new behavior for xen?

Xen makes a distinction between physical addresses and DMA addresses and
the latter can potentially be anywhere in the machine's real address
space while the former is what GFP_KERNEL etc controls.

You are using pci_pool_alloc which is the correct API to use for these
things since it's purpose is to handle cases where PHYS != DMA addr by
exposing the DMA address to the caller. As part of that you should also
be using dma_addr_t for DMA addresses since that is the type which is
defined to handle the appropriate DMA address size on the platform.

I think this DMA!=PHYS can also be true of some non-x86 architectures
without Xen too but I guess ioat is quite x86 specific? In any case it
is wrong, or at least non-portable, to use unsigned long for these
addresses even though it happens on x86 that physaddr == dma addr


Ian Campbell

Start every day off with a smile and get it over with.
-- W. C. Fields

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