vfio: Provide module option to disable vfio_iommu_type1 hugepage support

Add a module option to vfio_iommu_type1 to disable IOMMU hugepage
support.  This causes iommu_map to only be called with single page
mappings, disabling the IOMMU driver's ability to use hugepages.
This option can be enabled by loading vfio_iommu_type1 with
disable_hugepages=1 or dynamically through sysfs.  If enabled
dynamically, only new mappings are restricted.
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/vfio_iommu_type1.c

@@ -48,6 +48,12 @@ module_param_named(allow_unsafe_interrupts,
 MODULE_PARM_DESC(allow_unsafe_interrupts,
 		 "Enable VFIO IOMMU support for on platforms without interrupt remapping support.");
 
+static bool disable_hugepages;
+module_param_named(disable_hugepages,
+		   disable_hugepages, bool, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(disable_hugepages,
+		 "Disable VFIO IOMMU support for IOMMU hugepages.");
+
 struct vfio_iommu {
 	struct iommu_domain	*domain;
 	struct mutex		lock;
@@ -270,6 +276,11 @@ static long vfio_pin_pages(unsigned long vaddr, long npage,
 		return -ENOMEM;
 	}
 
+	if (unlikely(disable_hugepages)) {
+		vfio_lock_acct(1);
+		return 1;
+	}
+
 	/* Lock all the consecutive pages from pfn_base */
 	for (i = 1, vaddr += PAGE_SIZE; i < npage; i++, vaddr += PAGE_SIZE) {
 		unsigned long pfn = 0;