Re: [Xen-devel] [PATCH v2 2/4] x86/MSI-X: access MSI-X table only after having enabled MSI-X

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 10.04.15 at 22:02, <konrad.wilk@xxxxxxxxxx> wrote:
> On Wed, Mar 25, 2015 at 04:39:49PM +0000, Jan Beulich wrote:
>> As done in Linux by f598282f51 ("PCI: Fix the NIU MSI-X problem in a
>> better way") and its broken predecessor, make sure we don't access the
>> MSI-X table without having enabled MSI-X first, using the mask-all flag
>> instead to prevent interrupts from occurring.
> 
> This causes an regression with an Linux guest that has the XSA120 + XSA120
> addendum with PV guests (hadn't tried yet HVM).

You mentioning XSA-120 and its addendum - are these requirements
for the problem to be seen? I admit I may have tested a PV guest
only with an SR-IOV VF (and only a HVM guest also with an "ordinary"
device), but I'd like to be clear about the validity of the connection.

> When PV guest requests an MSI-X, pciback gets:
> 
> [  122.778654] xen-pciback: 0000:0a:00.0: enable MSI-X
> [  122.778861] pciback 0000:0a:00.0: xen map irq failed -6 for 1 domain
> [  122.778887] xen_pciback: 0000:0a:00.0: error enabling MSI-X for guest 1: 
> err -6!

Yeah, there were a few adjustments necessary to get similar issues
under control for HVM guests - maybe there's a path left not covered
by what's done for HVM guests.

> The device has the PCI_COMMAND enabled correctly:
> 
> # lspci -s 0a:0.0 -vvv | head
> 0a:00.0 Ethernet controller: Intel Corporation 82576 Gigabit Network 
> Connection (rev 01)
>         Subsystem: Super Micro Computer Inc Device 10c9
>         Control: I/O+ Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- 
> Stepping- SERR- FastB2B- DisINTx-
> 
> Attaching the 'xl dmesg', 'dmesg', and 'lspci'

Right - MSI-X is still disabled if the lspci really matches the state at
the time the failure occurred. I'm attaching the original patch with
some debugging code left in, which I suppose would show where
the problematic path is in case you can get to it before I would.

Jan

Attachment: x86-MSI-X-enable.patch
Description: Text document

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