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From:   Dexuan Cui <decui@microsoft.com>
To:     Marc Zyngier <maz@kernel.org>, Thomas Gleixner <tglx@linutronix.de>
CC:     KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Sasha Levin <sashal@kernel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        Michael Kelley <mikelley@microsoft.com>,
        "Lili Deng (Wicresoft North America Ltd)" <v-lide@microsoft.com>
Subject: [PATCH] irqdomain: Add the missing assignment of domain->fwnode for
 named fwnode
Thread-Topic: [PATCH] irqdomain: Add the missing assignment of domain->fwnode
 for named fwnode
Thread-Index: AdVh4blqLc5rFg83RpSOwiBFpYO6dw==
Date:   Mon, 2 Sep 2019 23:14:56 +0000
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Recently device pass-through stops working for Linux VM running on Hyper-V.

git-bisect shows the regression is caused by the recent commit
467a3bb97432 ("PCI: hv: Allocate a named fwnode ..."), but the root cause
is that the commit d59f6617eef0 forgets to set the domain->fwnode for
IRQCHIP_FWNODE_NAMED*, and as a result:

1. The domain->fwnode remains to be NULL.

2. irq_find_matching_fwspec() returns NULL since "h->fwnode =3D=3D fwnode" =
is
false, and pci_set_bus_msi_domain() sets the Hyper-V PCI root bus's
msi_domain to NULL.

3. When the device is added onto the root bus, the device's dev->msi_domain
is set to NULL in pci_set_msi_domain().

4. When a device driver tries to enable MSI-X, pci_msi_setup_msi_irqs()
calls arch_setup_msi_irqs(), which uses the native MSI chip (i.e.
arch/x86/kernel/apic/msi.c: pci_msi_controller) to set up the irqs, but
actually pci_msi_setup_msi_irqs() is supposed to call
msi_domain_alloc_irqs() with the hbus->irq_domain, which is created in
hv_pcie_init_irq_domain() and is associated with the Hyper-V chip
hv_msi_irq_chip. Consequently, the irq line is not properly set up, and
the device driver can not receive any interrupt.

Fixes: d59f6617eef0 ("genirq: Allow fwnode to carry name information only")
Fixes: 467a3bb97432 ("PCI: hv: Allocate a named fwnode instead of an addres=
s-based one")
Reported-by: Lili Deng <v-lide@microsoft.com>
Signed-off-by: Dexuan Cui <decui@microsoft.com>
---

Note: the commit 467a3bb97432 ("PCI: hv: Allocate a named fwnode ...") has =
not
gone in Linus's tree yet (the commit is in linux-next for a while), so the =
commit ID
in the changelog can change when it goes in Linus's tree.

This patch works in my test, but I'm not 100% sure this is the right fix.=20

Looking forward to your comment!

 kernel/irq/irqdomain.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
index e7bbab149750..132672b74e4b 100644
--- a/kernel/irq/irqdomain.c
+++ b/kernel/irq/irqdomain.c
@@ -149,6 +149,7 @@ struct irq_domain *__irq_domain_add(struct fwnode_handl=
e *fwnode, int size,
 		switch (fwid->type) {
 		case IRQCHIP_FWNODE_NAMED:
 		case IRQCHIP_FWNODE_NAMED_ID:
+			domain->fwnode =3D fwnode;
 			domain->name =3D kstrdup(fwid->name, GFP_KERNEL);
 			if (!domain->name) {
 				kfree(domain);
--=20
2.19.1