Re: [Xen-devel] [BUG] XEN 4.3.3 - segfault in xl create for HVM with PCI passthrough

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 05/11/14 12:39, Ian Campbell wrote:
> On Wed, 2014-11-05 at 13:01 +0100, Atom2 wrote:
>
> Thanks for all that, sadly it's not giving me any clues what is going
> wrong :-/
>
>> To me, it looks as if something is broken with the PCI passthrough stuff 
>> and that has started with 4.3.3. Strangely however, valgrind seems to 
>> work around that issue insofar that no segfault happens. Is there any 
>> explanation of the different behaviour between native execution of xl 
>> and starting xl under valgrind's control?
> Valgrind has it's own memory allocator etc, but it's supposed to catch
> errors, not hide them. I think even 3.10.0 is missing support for some
> hypercalls which are being used by passthrough, which is why we are
> continuing to see different behaviours.
>
> I think we are reaching the point of diminishing returns with vagrind.
> It probably is worth rerunning with "-v --leak-check=full", but after
> that we'd be looking at adding valgrind patches for the new hypercalls,
> which I don't think will be worthwhile (although I intend to write the
> patches anyway).
>
> So unless "-v --leak-check=full" tells me something (which I'm doubtful
> of at this stage) I think we're back to bisecting the changes since
> 4.3.1, sorry.

The lack valgrind support for XEN_DOMCTL_test_assign is causing PCI
Passthrough to fail.

This is where "libxl: error: libxl_pci.c:1045:libxl__device_pci_add: PCI
device 0000:0a:0b.0 cannot be assigned - no IOMMU?" comes from.

While I do have 10 patches I really should get around to upstreaming
into valgrind, the passthrough hypercalls are not amongst them.  Fixing
XEN_DOMCTL_test_assign is only the first step.

~Andrew


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