FAILED: patch "[PATCH] x86/pci/xen: Disable PCI/MSI[-X] masking for XEN_HVM guests" failed to apply to 5.4-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 7e0815b3e09986d2fe651199363e135b9358132a Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Thu, 28 Apr 2022 15:50:54 +0200
Subject: [PATCH] x86/pci/xen: Disable PCI/MSI[-X] masking for XEN_HVM guests

When a XEN_HVM guest uses the XEN PIRQ/Eventchannel mechanism, then
PCI/MSI[-X] masking is solely controlled by the hypervisor, but contrary to
XEN_PV guests this does not disable PCI/MSI[-X] masking in the PCI/MSI
layer.

This can lead to a situation where the PCI/MSI layer masks an MSI[-X]
interrupt and the hypervisor grants the write despite the fact that it
already requested the interrupt. As a consequence interrupt delivery on the
affected device is not happening ever.

Set pci_msi_ignore_mask to prevent that like it's done for XEN_PV guests
already.

Fixes: 809f9267bbab ("xen: map MSIs into pirqs")
Reported-by: Jeremi Piotrowski <jpiotrowski@linux.microsoft.com>
Reported-by: Dusty Mabe <dustymabe@redhat.com>
Reported-by: Salvatore Bonaccorso <carnil@debian.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Noah Meyerhans <noahm@debian.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/87tuaduxj5.ffs@tglx

diff --git a/arch/x86/pci/xen.c b/arch/x86/pci/xen.c
index 9bb1e2941179..b94f727251b6 100644
--- a/arch/x86/pci/xen.c
+++ b/arch/x86/pci/xen.c
@@ -467,7 +467,6 @@ static __init void xen_setup_pci_msi(void)
 		else
 			xen_msi_ops.setup_msi_irqs = xen_setup_msi_irqs;
 		xen_msi_ops.teardown_msi_irqs = xen_pv_teardown_msi_irqs;
-		pci_msi_ignore_mask = 1;
 	} else if (xen_hvm_domain()) {
 		xen_msi_ops.setup_msi_irqs = xen_hvm_setup_msi_irqs;
 		xen_msi_ops.teardown_msi_irqs = xen_teardown_msi_irqs;
@@ -481,6 +480,11 @@ static __init void xen_setup_pci_msi(void)
 	 * in allocating the native domain and never use it.
 	 */
 	x86_init.irqs.create_pci_msi_domain = xen_create_pci_msi_domain;
+	/*
+	 * With XEN PIRQ/Eventchannels in use PCI/MSI[-X] masking is solely
+	 * controlled by the hypervisor.
+	 */
+	pci_msi_ignore_mask = 1;
 }
 
 #else /* CONFIG_PCI_MSI */