[Xen-users] Crash while mapping a device's (large) memory region

[Quentin Garnier <qgarnier@xxxxxxxxxxxx>]

Hi,

I'm getting a crash trying to map more than 0x106 pages of a device's
memory region.

I'm using Xen-unstable from a few days ago (monday, I think), so it's a
2.6.16.13 kernel.

I have a device which has a 32MB-long memory region.  I've written a
very simple module to merely let userland mmap that region to expose the
issue I'm seeing.  The module is basically down to that:

In probe():
        base_addr = pci_resource_start(dev, 2);

In mmap():
        remap_pfn_range(vma, vma->vm_start, base_addr >> PAGE_SHIFT,
            vma->vm_end - vma->vm_start, vma->vm_page_prot);

Then I made a simple userland tool that mmap()s the device for a size
given as an argument.  I could see that I can map up to 0x106000 bytes,
but trying one more page gets me a crash in dom0, apparently in
hypercall_page, fore HYPERCALL_update_va_mapping().  It's hard to tell
what exactly happens though, but the trace seems to indicate it comes
from remap_pfn_range through remap_pte_range.

I really can't make sense of that value, and I don't think I understand
enough of Xen's internal to go further with debugging without some help,
so here I post, looking for clues about what happens.

The module work fines under an i386 kernel compiled from the same
sources.

Then again, my use of remap_pfn_range might be wrong, but why that 0x106
number anyway (it's 1MB and 6 pages)?

Quentin Garnier.

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