[PATCH] PCI: hv: fix "spurious APIC interrupt" due to new vector reservation mode

[Dexuan Cui]

Last month the vector management code was reworked, and as a result of the
changes, e.g. commit 22d0b12f3560 ("genirq/irqdomain: Add force
reactivation flag to irq domains"), commit 4900be83602b ("x86/vector/msi:
Switch to global reservation mode") etc, now we must add this new flag
MSI_FLAG_MUST_REACTIVATE when calling pci_msi_create_irq_domain() on x86,
otherwise Hyper-V PCIe pass-through can't work, and we get:
"spurious APIC interrupt through vector ff on CPU#0, should never happen",
this is because no valid MSI/MSI-X vector is allocated.

Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Cc: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
Cc: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>
---

Currently the "reservation mode" patchset has not been in Linus's tree yet, so
today's mainline hasn't shown the issue, but today's linux-next has shown the
issue (PCIe pass-through on Hyper-V can't work).

I think any caller of pci_msi_create_irq_domain() that runs on x86 needs to
be updated, but besides pci-hyper I'm not sure which callers run on x86.

 drivers/pci/host/pci-hyperv.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/host/pci-hyperv.c b/drivers/pci/host/pci-hyperv.c
index 0fe3ea1..35a7683 100644
--- a/drivers/pci/host/pci-hyperv.c
+++ b/drivers/pci/host/pci-hyperv.c
@@ -1196,7 +1196,8 @@ static int hv_pcie_init_irq_domain(struct hv_pcibus_device *hbus)
 	hbus->msi_info.ops = &hv_msi_ops;
 	hbus->msi_info.flags = (MSI_FLAG_USE_DEF_DOM_OPS |
 		MSI_FLAG_USE_DEF_CHIP_OPS | MSI_FLAG_MULTI_PCI_MSI |
-		MSI_FLAG_PCI_MSIX);
+		MSI_FLAG_PCI_MSIX |
+		MSI_FLAG_MUST_REACTIVATE);
 	hbus->msi_info.handler = handle_edge_irq;
 	hbus->msi_info.handler_name = "edge";
 	hbus->msi_info.data = hbus;
-- 
2.7.4