[PATCH 2/3] vfio/type1: prepare for batched pinning with struct vfio_batch

[Daniel Jordan]

Get ready to pin more pages at once with struct vfio_batch, which
represents a batch of pinned pages.

The struct has a fallback page pointer to avoid two unlikely scenarios:
pointlessly allocating a page if disable_hugepages is enabled or failing
the whole pinning operation if the kernel can't allocate memory.

vaddr_get_pfn() becomes vaddr_get_pfns() to prepare for handling
multiple pages, though for now only one page is stored in the pages
array.

Signed-off-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
---
 drivers/vfio/vfio_iommu_type1.c | 71 +++++++++++++++++++++++++++------
 1 file changed, 58 insertions(+), 13 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 4d608bc552a4..c26c1a4697e5 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -97,6 +97,12 @@ struct vfio_dma {
 	unsigned long		*bitmap;
 };
 
+struct vfio_batch {
+	struct page		**pages;	/* for pin_user_pages_remote */
+	struct page		*fallback_page; /* if pages alloc fails */
+	int			capacity;	/* length of pages array */
+};
+
 struct vfio_group {
 	struct iommu_group	*iommu_group;
 	struct list_head	next;
@@ -415,6 +421,31 @@ static int put_pfn(unsigned long pfn, int prot)
 	return 0;
 }
 
+#define VFIO_BATCH_MAX_CAPACITY (PAGE_SIZE / sizeof(struct page *))
+
+static void vfio_batch_init(struct vfio_batch *batch)
+{
+	if (unlikely(disable_hugepages))
+		goto fallback;
+
+	batch->pages = (struct page **) __get_free_page(GFP_KERNEL);
+	if (!batch->pages)
+		goto fallback;
+
+	batch->capacity = VFIO_BATCH_MAX_CAPACITY;
+	return;
+
+fallback:
+	batch->pages = &batch->fallback_page;
+	batch->capacity = 1;
+}
+
+static void vfio_batch_fini(struct vfio_batch *batch)
+{
+	if (batch->capacity == VFIO_BATCH_MAX_CAPACITY)
+		free_page((unsigned long)batch->pages);
+}
+
 static int follow_fault_pfn(struct vm_area_struct *vma, struct mm_struct *mm,
 			    unsigned long vaddr, unsigned long *pfn,
 			    bool write_fault)
@@ -445,10 +476,10 @@ static int follow_fault_pfn(struct vm_area_struct *vma, struct mm_struct *mm,
  * Returns the positive number of pfns successfully obtained or a negative
  * error code.
  */
-static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
-			 int prot, unsigned long *pfn)
+static int vaddr_get_pfns(struct mm_struct *mm, unsigned long vaddr,
+			  long npages, int prot, unsigned long *pfn,
+			  struct page **pages)
 {
-	struct page *page[1];
 	struct vm_area_struct *vma;
 	unsigned int flags = 0;
 	int ret;
@@ -457,10 +488,10 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
 		flags |= FOLL_WRITE;
 
 	mmap_read_lock(mm);
-	ret = pin_user_pages_remote(mm, vaddr, 1, flags | FOLL_LONGTERM,
-				    page, NULL, NULL);
-	if (ret == 1) {
-		*pfn = page_to_pfn(page[0]);
+	ret = pin_user_pages_remote(mm, vaddr, npages, flags | FOLL_LONGTERM,
+				    pages, NULL, NULL);
+	if (ret > 0) {
+		*pfn = page_to_pfn(pages[0]);
 		goto done;
 	}
 
@@ -493,7 +524,7 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
  */
 static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
 				  long npage, unsigned long *pfn_base,
-				  unsigned long limit)
+				  unsigned long limit, struct vfio_batch *batch)
 {
 	unsigned long pfn = 0;
 	long ret, pinned = 0, lock_acct = 0;
@@ -504,7 +535,8 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
 	if (!current->mm)
 		return -ENODEV;
 
-	ret = vaddr_get_pfn(current->mm, vaddr, dma->prot, pfn_base);
+	ret = vaddr_get_pfns(current->mm, vaddr, 1, dma->prot, pfn_base,
+			     batch->pages);
 	if (ret < 0)
 		return ret;
 
@@ -531,7 +563,8 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
 	/* Lock all the consecutive pages from pfn_base */
 	for (vaddr += PAGE_SIZE, iova += PAGE_SIZE; pinned < npage;
 	     pinned++, vaddr += PAGE_SIZE, iova += PAGE_SIZE) {
-		ret = vaddr_get_pfn(current->mm, vaddr, dma->prot, &pfn);
+		ret = vaddr_get_pfns(current->mm, vaddr, 1, dma->prot, &pfn,
+				     batch->pages);
 		if (ret < 0)
 			break;
 
@@ -594,6 +627,7 @@ 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 mm_struct *mm;
 	int ret;
 
@@ -601,7 +635,7 @@ static int vfio_pin_page_external(struct vfio_dma *dma, unsigned long vaddr,
 	if (!mm)
 		return -ENODEV;
 
-	ret = vaddr_get_pfn(mm, vaddr, dma->prot, pfn_base);
+	ret = vaddr_get_pfns(mm, vaddr, 1, dma->prot, pfn_base, pages);
 	if (ret == 1 && do_accounting && !is_invalid_reserved_pfn(*pfn_base)) {
 		ret = vfio_lock_acct(dma, 1, true);
 		if (ret) {
@@ -1246,15 +1280,19 @@ static int vfio_pin_map_dma(struct vfio_iommu *iommu, struct vfio_dma *dma,
 {
 	dma_addr_t iova = dma->iova;
 	unsigned long vaddr = dma->vaddr;
+	struct vfio_batch batch;
 	size_t size = map_size;
 	long npage;
 	unsigned long pfn, limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
 	int ret = 0;
 
+	vfio_batch_init(&batch);
+
 	while (size) {
 		/* Pin a contiguous chunk of memory */
 		npage = vfio_pin_pages_remote(dma, vaddr + dma->size,
-					      size >> PAGE_SHIFT, &pfn, limit);
+					      size >> PAGE_SHIFT, &pfn, limit,
+					      &batch);
 		if (npage <= 0) {
 			WARN_ON(!npage);
 			ret = (int)npage;
@@ -1274,6 +1312,7 @@ static int vfio_pin_map_dma(struct vfio_iommu *iommu, struct vfio_dma *dma,
 		dma->size += npage << PAGE_SHIFT;
 	}
 
+	vfio_batch_fini(&batch);
 	dma->iommu_mapped = true;
 
 	if (ret)
@@ -1432,6 +1471,7 @@ static int vfio_bus_type(struct device *dev, void *data)
 static int vfio_iommu_replay(struct vfio_iommu *iommu,
 			     struct vfio_domain *domain)
 {
+	struct vfio_batch batch;
 	struct vfio_domain *d = NULL;
 	struct rb_node *n;
 	unsigned long limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
@@ -1442,6 +1482,8 @@ static int vfio_iommu_replay(struct vfio_iommu *iommu,
 		d = list_first_entry(&iommu->domain_list,
 				     struct vfio_domain, next);
 
+	vfio_batch_init(&batch);
+
 	n = rb_first(&iommu->dma_list);
 
 	for (; n; n = rb_next(n)) {
@@ -1489,7 +1531,8 @@ static int vfio_iommu_replay(struct vfio_iommu *iommu,
 
 				npage = vfio_pin_pages_remote(dma, vaddr,
 							      n >> PAGE_SHIFT,
-							      &pfn, limit);
+							      &pfn, limit,
+							      &batch);
 				if (npage <= 0) {
 					WARN_ON(!npage);
 					ret = (int)npage;
@@ -1522,6 +1565,7 @@ static int vfio_iommu_replay(struct vfio_iommu *iommu,
 		dma->iommu_mapped = true;
 	}
 
+	vfio_batch_fini(&batch);
 	return 0;
 
 unwind:
@@ -1562,6 +1606,7 @@ static int vfio_iommu_replay(struct vfio_iommu *iommu,
 		}
 	}
 
+	vfio_batch_fini(&batch);
 	return ret;
 }
 
-- 
2.30.0