AMD IOMMU: make interrupt work again

Commit 899110e3 ("AMD IOMMU: include IOMMU interrupt information in 'M'
debug key output") made the AMD IOMMU MSI setup code use more of the
generic MSI setup code (as other than for VT-d this is an ordinary MSI-
capable PCI device), but failed to notice that till now interrupt setup
there _required_ the subsequent affinity setup to be done, as that was
the only point where the MSI message would get written. The generic MSI
affinity setting routine, however, does only an incremental change,
i.e. relies on this setup to have been done before.

In order to not make the code even more clumsy, introduce a new low
level helper routine __setup_msi_irq(), thus eliminating the need for
the AMD IOMMU code to directly fiddle with the IRQ descriptor.

Reported-by: Suravee Suthikulanit <suravee.suthikulpanit@xxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/msi.c
+++ b/xen/arch/x86/msi.c
@@ -472,11 +472,18 @@ static struct msi_desc* alloc_msi_entry(
 
 int setup_msi_irq(struct irq_desc *desc, struct msi_desc *msidesc)
 {
+    return __setup_msi_irq(desc, msidesc,
+                           msi_maskable_irq(msidesc) ? &pci_msi_maskable
+                                                     : &pci_msi_nonmaskable);
+}
+
+int __setup_msi_irq(struct irq_desc *desc, struct msi_desc *msidesc,
+                    hw_irq_controller *handler)
+{
     struct msi_msg msg;
 
     desc->msi_desc = msidesc;
-    desc->handler = msi_maskable_irq(msidesc) ? &pci_msi_maskable
-                                              : &pci_msi_nonmaskable;
+    desc->handler = handler;
     msi_compose_msg(desc, &msg);
     return write_msi_msg(msidesc, &msg);
 }
--- a/xen/drivers/passthrough/amd/iommu_init.c
+++ b/xen/drivers/passthrough/amd/iommu_init.c
@@ -748,7 +748,7 @@ static void iommu_interrupt_handler(int 
 static bool_t __init set_iommu_interrupt_handler(struct amd_iommu *iommu)
 {
     int irq, ret;
-    struct irq_desc *desc;
+    hw_irq_controller *handler;
     unsigned long flags;
     u16 control;
 
@@ -759,7 +759,6 @@ static bool_t __init set_iommu_interrupt
         return 0;
     }
 
-    desc = irq_to_desc(irq);
     spin_lock_irqsave(&pcidevs_lock, flags);
     iommu->msi.dev = pci_get_pdev(iommu->seg, PCI_BUS(iommu->bdf),
                                   PCI_DEVFN2(iommu->bdf));
@@ -771,7 +770,6 @@ static bool_t __init set_iommu_interrupt
                         PCI_SLOT(iommu->bdf), PCI_FUNC(iommu->bdf));
         return 0;
     }
-    desc->msi_desc = &iommu->msi;
     control = pci_conf_read16(iommu->seg, PCI_BUS(iommu->bdf),
                               PCI_SLOT(iommu->bdf), PCI_FUNC(iommu->bdf),
                               iommu->msi.msi_attrib.pos + PCI_MSI_FLAGS);
@@ -781,14 +779,15 @@ static bool_t __init set_iommu_interrupt
         iommu->msi.msi_attrib.maskbit = 1;
         iommu->msi.msi.mpos = msi_mask_bits_reg(iommu->msi.msi_attrib.pos,
                                                 is_64bit_address(control));
-        desc->handler = &iommu_maskable_msi_type;
+        handler = &iommu_maskable_msi_type;
     }
     else
-        desc->handler = &iommu_msi_type;
-    ret = request_irq(irq, iommu_interrupt_handler, 0, "amd_iommu", iommu);
+        handler = &iommu_msi_type;
+    ret = __setup_msi_irq(irq_to_desc(irq), &iommu->msi, handler);
+    if ( !ret )
+        ret = request_irq(irq, iommu_interrupt_handler, 0, "amd_iommu", iommu);
     if ( ret )
     {
-        desc->handler = &no_irq_type;
         destroy_irq(irq);
         AMD_IOMMU_DEBUG("can't request irq\n");
         return 0;
--- a/xen/include/asm-x86/msi.h
+++ b/xen/include/asm-x86/msi.h
@@ -72,6 +72,7 @@ struct msi_msg {
 };
 
 struct irq_desc;
+struct hw_interrupt_type;
 struct msi_desc;
 /* Helper functions */
 extern int pci_enable_msi(struct msi_info *msi, struct msi_desc **desc);
@@ -79,6 +80,8 @@ extern void pci_disable_msi(struct msi_d
 extern int pci_prepare_msix(u16 seg, u8 bus, u8 devfn, bool_t off);
 extern void pci_cleanup_msi(struct pci_dev *pdev);
 extern int setup_msi_irq(struct irq_desc *, struct msi_desc *);
+extern int __setup_msi_irq(struct irq_desc *, struct msi_desc *,
+                           const struct hw_interrupt_type *);
 extern void teardown_msi_irq(int irq);
 extern int msi_free_vector(struct msi_desc *entry);
 extern int pci_restore_msi_state(struct pci_dev *pdev);