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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

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).

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!

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'

The guest config is
[konrad@build-external tst036]$ more pf-pv.xm
extra="console=hvc0 debug "
kernel="/mnt/lab/bootstrap-x86_64/vmlinuz"
ramdisk="/mnt/lab/bootstrap-x86_64/initramfs.cpio.gz"
memory=2048
vcpus=6
name="pv-pf"
on_crash="preserve"
pci=["0000:0a:0.0"];

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