[PATCH] x86/xen: Set MSI_FLAG_PCI_MSIX support in Xen MSI domain

David Woodhouse
2023-01-15T22:14:39Z

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The Xen MSI → PIRQ magic does support MSI-X, so advertise it.

(In fact it's better off with MSI-X than MSI, because it's actually
broken by design for 32-bit MSI, since it puts the high bits of the
PIRQ# into the high 32 bits of the MSI message address, instead of the
Extended Destination ID field which is in bits 4-11.

Strictly speaking, this really fixes a much older commit 2e4386eba0c0
("x86/xen: Wrap XEN MSI management into irqdomain") which failed to set
the flag. But that never really mattered until __pci_enable_msix_range()
started to check and bail out early. So in 6.2-rc we see failures e.g.
to bring up networking on an Amazon EC2 m4.16xlarge instance:

[ 41.498694] ena 0000:00:03.0 (unnamed net_device) (uninitialized): Failed to enable MSI-X. irq_cnt -524
[ 41.498705] ena 0000:00:03.0: Can not reserve msix vectors
[ 41.498712] ena 0000:00:03.0: Failed to enable and set the admin interrupts

Side note: This is the first bug found, and first patch tested, by running
Xen guests under QEMU/KVM instead of running under actual Xen.

Fixes: 99f3d2797657 ("PCI/MSI: Reject MSI-X early")
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
arch/x86/pci/xen.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/arch/x86/pci/xen.c b/arch/x86/pci/xen.c
index b94f727251b6..790550479831 100644
--- a/arch/x86/pci/xen.c
+++ b/arch/x86/pci/xen.c
@@ -433,6 +433,7 @@ static struct msi_domain_ops xen_pci_msi_domain_ops = {
};

static struct msi_domain_info xen_pci_msi_domain_info = {
+ .flags = MSI_FLAG_PCI_MSIX,
.ops = &xen_pci_msi_domain_ops,
};

--
2.34.1

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