linux-kernel - [tip: x86/urgent] x86/pci/xen: Set MSI_FLAG_PCI

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Message-ID: <167389820601.4906.4662164438390754868.tip-bot2@tip-bot2>
Date:   Mon, 16 Jan 2023 19:43:26 -0000
From:   "tip-bot2 for David Woodhouse" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     David Woodhouse <dwmw@...zon.co.uk>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/pci/xen: Set MSI_FLAG_PCI_MSIX support in Xen
 MSI domain

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     0a3a58de319552525507a3497da86df039a5e4e0
Gitweb:        https://git.kernel.org/tip/0a3a58de319552525507a3497da86df039a5e4e0
Author:        David Woodhouse <dwmw2@...radead.org>
AuthorDate:    Sun, 15 Jan 2023 22:14:19 
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Mon, 16 Jan 2023 20:40:44 +01:00

x86/pci/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>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Link: https://lore.kernel.org/r/4bffa69a949bfdc92c4a18e5a1c3cbb3b94a0d32.camel@infradead.org

---
 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 b94f727..7905504 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,
 };