linux-kernel - [PATCH] x86/xen: Set MSI_FLAG_PCI

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Message-ID: <4bffa69a949bfdc92c4a18e5a1c3cbb3b94a0d32.camel@infradead.org>
Date:   Sun, 15 Jan 2023 22:14:19 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        xen-devel <xen-devel@...ts.xenproject.org>,
        Juergen Gross <jgross@...e.com>
Cc:     x86@...nel.org, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>, linux-pci@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Marc Zyngier <maz@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Ashok Raj <ashok.raj@...el.com>, Jon Mason <jdmason@...zu.us>,
        Allen Hubbe <allenbh@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        linuxppc-dev@...ts.ozlabs.org,
        "Ahmed S. Darwish" <darwi@...utronix.de>,
        Reinette Chatre <reinette.chatre@...el.com>
Subject: [PATCH] x86/xen: Set MSI_FLAG_PCI_MSIX support in Xen MSI domain

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@...zon.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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