vfio/type1: Convert all vaddr_get_pfns() callers to use vfio_batch

This is a step towards passing the structure to vaddr_get_pfns()
directly in order to provide greater distinction between page backed
pfns and pfnmaps.

Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Mitchell Augustin <mitchell.augustin@canonical.com>
Tested-by: Mitchell Augustin <mitchell.augustin@canonical.com>
Link: https://lore.kernel.org/r/20250218222209.1382449-3-alex.williamson@redhat.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

Author: Alex Williamson

drivers/vfio/vfio_iommu_type1.c

@@ -471,12 +471,12 @@ static int put_pfn(unsigned long pfn, int prot)
 
 #define VFIO_BATCH_MAX_CAPACITY (PAGE_SIZE / sizeof(struct page *))
 
-static void vfio_batch_init(struct vfio_batch *batch)
+static void __vfio_batch_init(struct vfio_batch *batch, bool single)
 {
 	batch->size = 0;
 	batch->offset = 0;
 
-	if (unlikely(disable_hugepages))
+	if (single || unlikely(disable_hugepages))
 		goto fallback;
 
 	batch->pages = (struct page **) __get_free_page(GFP_KERNEL);
@@ -491,6 +491,16 @@ static void vfio_batch_init(struct vfio_batch *batch)
 	batch->capacity = 1;
 }
 
+static void vfio_batch_init(struct vfio_batch *batch)
+{
+	__vfio_batch_init(batch, false);
+}
+
+static void vfio_batch_init_single(struct vfio_batch *batch)
+{
+	__vfio_batch_init(batch, true);
+}
+
 static void vfio_batch_unpin(struct vfio_batch *batch, struct vfio_dma *dma)
 {
 	while (batch->size) {
@@ -730,15 +740,17 @@ static long vfio_unpin_pages_remote(struct vfio_dma *dma, dma_addr_t iova,
 static int vfio_pin_page_external(struct vfio_dma *dma, unsigned long vaddr,
 				  unsigned long *pfn_base, bool do_accounting)
 {
-	struct page *pages[1];
+	struct vfio_batch batch;
 	struct mm_struct *mm;
 	int ret;
 
 	mm = dma->mm;
 	if (!mmget_not_zero(mm))
 		return -ENODEV;
 
-	ret = vaddr_get_pfns(mm, vaddr, 1, dma->prot, pfn_base, pages);
+	vfio_batch_init_single(&batch);
+
+	ret = vaddr_get_pfns(mm, vaddr, 1, dma->prot, pfn_base, batch.pages);
 	if (ret != 1)
 		goto out;
 
@@ -757,6 +769,7 @@ static int vfio_pin_page_external(struct vfio_dma *dma, unsigned long vaddr,
 	}
 
 out:
+	vfio_batch_fini(&batch);
 	mmput(mm);
 	return ret;
 }