AMD IOMMU: fix an init time spinlock flaw

pcidevs_lock doesn't require interrupts to be disabled while being acquired.
However there remains an exception in AMD IOMMU code, where the lock is
acquired with interrupt disabled. This inconsistency might lead to deadlock.

The fix is straightforward to use spin_lock instead. Also interrupt has been
enabled when this function is invoked, so we're sure consistency around
pcidevs_lock can be guaranteed after this fix.

Signed-off-by: Quan Xu <quan.xu@intel.com>
Reviewed-by: Dario Faggioli <dario.faggioli@citrix.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/drivers/passthrough/amd/iommu_init.c

@@ -778,7 +778,6 @@ static bool_t __init set_iommu_interrupt_handler(struct amd_iommu *iommu)
 {
     int irq, ret;
     hw_irq_controller *handler;
-    unsigned long flags;
     u16 control;
 
     irq = create_irq(NUMA_NO_NODE);
@@ -788,10 +787,10 @@ static bool_t __init set_iommu_interrupt_handler(struct amd_iommu *iommu)
         return 0;
     }
 
-    spin_lock_irqsave(&pcidevs_lock, flags);
+    spin_lock(&pcidevs_lock);
     iommu->msi.dev = pci_get_pdev(iommu->seg, PCI_BUS(iommu->bdf),
                                   PCI_DEVFN2(iommu->bdf));
-    spin_unlock_irqrestore(&pcidevs_lock, flags);
+    spin_unlock(&pcidevs_lock);
     if ( !iommu->msi.dev )
     {
         AMD_IOMMU_DEBUG("IOMMU: no pdev for %04x:%02x:%02x.%u\n",