udmabuf: add back support for mapping hugetlb pages

A user or admin can configure a VMM (Qemu) Guest's memory to be backed by
hugetlb pages for various reasons.  However, a Guest OS would still
allocate (and pin) buffers that are backed by regular 4k sized pages.  In
order to map these buffers and create dma-bufs for them on the Host, we
first need to find the hugetlb pages where the buffer allocations are
located and then determine the offsets of individual chunks (within those
pages) and use this information to eventually populate a scatterlist.

Testcase: default_hugepagesz=2M hugepagesz=2M hugepages=2500 options
were passed to the Host kernel and Qemu was launched with these
relevant options: qemu-system-x86_64 -m 4096m....
-device virtio-gpu-pci,max_outputs=1,blob=true,xres=1920,yres=1080
-display gtk,gl=on
-object memory-backend-memfd,hugetlb=on,id=mem1,size=4096M
-machine memory-backend=mem1

Replacing -display gtk,gl=on with -display gtk,gl=off above would
exercise the mmap handler.

Link: https://lkml.kernel.org/r/20240624063952.1572359-7-vivek.kasireddy@intel.com
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Acked-by: Mike Kravetz <mike.kravetz@oracle.com> (v2)
Acked-by: Dave Airlie <airlied@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Hugh Dickins <hughd@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Dongwon Kim <dongwon.kim@intel.com>
Cc: Junxiao Chang <junxiao.chang@intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

drivers/dma-buf/udmabuf.c

@@ -10,6 +10,7 @@
 #include <linux/miscdevice.h>
 #include <linux/module.h>
 #include <linux/shmem_fs.h>
+#include <linux/hugetlb.h>
 #include <linux/slab.h>
 #include <linux/udmabuf.h>
 #include <linux/vmalloc.h>
@@ -28,6 +29,7 @@ struct udmabuf {
 	struct page **pages;
 	struct sg_table *sg;
 	struct miscdevice *device;
+	pgoff_t *offsets;
 };
 
 static vm_fault_t udmabuf_vm_fault(struct vm_fault *vmf)
@@ -41,6 +43,8 @@ static vm_fault_t udmabuf_vm_fault(struct vm_fault *vmf)
 		return VM_FAULT_SIGBUS;
 
 	pfn = page_to_pfn(ubuf->pages[pgoff]);
+	pfn += ubuf->offsets[pgoff] >> PAGE_SHIFT;
+
 	return vmf_insert_pfn(vma, vmf->address, pfn);
 }
 
@@ -90,23 +94,29 @@ static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf,
 {
 	struct udmabuf *ubuf = buf->priv;
 	struct sg_table *sg;
+	struct scatterlist *sgl;
+	unsigned int i = 0;
 	int ret;
 
 	sg = kzalloc(sizeof(*sg), GFP_KERNEL);
 	if (!sg)
 		return ERR_PTR(-ENOMEM);
-	ret = sg_alloc_table_from_pages(sg, ubuf->pages, ubuf->pagecount,
-					0, ubuf->pagecount << PAGE_SHIFT,
-					GFP_KERNEL);
+
+	ret = sg_alloc_table(sg, ubuf->pagecount, GFP_KERNEL);
 	if (ret < 0)
-		goto err;
+		goto err_alloc;
+
+	for_each_sg(sg->sgl, sgl, ubuf->pagecount, i)
+		sg_set_page(sgl, ubuf->pages[i], PAGE_SIZE, ubuf->offsets[i]);
+
 	ret = dma_map_sgtable(dev, sg, direction, 0);
 	if (ret < 0)
-		goto err;
+		goto err_map;
 	return sg;
 
-err:
+err_map:
 	sg_free_table(sg);
+err_alloc:
 	kfree(sg);
 	return ERR_PTR(ret);
 }
@@ -143,6 +153,7 @@ static void release_udmabuf(struct dma_buf *buf)
 
 	for (pg = 0; pg < ubuf->pagecount; pg++)
 		put_page(ubuf->pages[pg]);
+	kfree(ubuf->offsets);
 	kfree(ubuf->pages);
 	kfree(ubuf);
 }
@@ -196,17 +207,77 @@ static const struct dma_buf_ops udmabuf_ops = {
 #define SEALS_WANTED (F_SEAL_SHRINK)
 #define SEALS_DENIED (F_SEAL_WRITE)
 
+static int handle_hugetlb_pages(struct udmabuf *ubuf, struct file *memfd,
+				pgoff_t offset, pgoff_t pgcnt,
+				pgoff_t *pgbuf)
+{
+	struct hstate *hpstate = hstate_file(memfd);
+	pgoff_t mapidx = offset >> huge_page_shift(hpstate);
+	pgoff_t subpgoff = (offset & ~huge_page_mask(hpstate)) >> PAGE_SHIFT;
+	pgoff_t maxsubpgs = huge_page_size(hpstate) >> PAGE_SHIFT;
+	struct page *hpage = NULL;
+	struct folio *folio;
+	pgoff_t pgidx;
+
+	mapidx <<= huge_page_order(hpstate);
+	for (pgidx = 0; pgidx < pgcnt; pgidx++) {
+		if (!hpage) {
+			folio = __filemap_get_folio(memfd->f_mapping,
+						    mapidx,
+						    FGP_ACCESSED, 0);
+			if (IS_ERR(folio))
+				return PTR_ERR(folio);
+
+			hpage = &folio->page;
+		}
+
+		get_page(hpage);
+		ubuf->pages[*pgbuf] = hpage;
+		ubuf->offsets[*pgbuf] = subpgoff << PAGE_SHIFT;
+		(*pgbuf)++;
+		if (++subpgoff == maxsubpgs) {
+			put_page(hpage);
+			hpage = NULL;
+			subpgoff = 0;
+			mapidx += pages_per_huge_page(hpstate);
+		}
+	}
+
+	if (hpage)
+		put_page(hpage);
+
+	return 0;
+}
+
+static int handle_shmem_pages(struct udmabuf *ubuf, struct file *memfd,
+			      pgoff_t offset, pgoff_t pgcnt,
+			      pgoff_t *pgbuf)
+{
+	pgoff_t pgidx, pgoff = offset >> PAGE_SHIFT;
+	struct page *page;
+
+	for (pgidx = 0; pgidx < pgcnt; pgidx++) {
+		page = shmem_read_mapping_page(memfd->f_mapping,
+					       pgoff + pgidx);
+		if (IS_ERR(page))
+			return PTR_ERR(page);
+
+		ubuf->pages[*pgbuf] = page;
+		(*pgbuf)++;
+	}
+
+	return 0;
+}
+
 static long udmabuf_create(struct miscdevice *device,
 			   struct udmabuf_create_list *head,
 			   struct udmabuf_create_item *list)
 {
 	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
 	struct file *memfd = NULL;
-	struct address_space *mapping = NULL;
 	struct udmabuf *ubuf;
 	struct dma_buf *buf;
-	pgoff_t pgoff, pgcnt, pgidx, pgbuf = 0, pglimit;
-	struct page *page;
+	pgoff_t pgcnt, pgbuf = 0, pglimit;
 	int seals, ret = -EINVAL;
 	u32 i, flags;
 
@@ -234,15 +305,20 @@ static long udmabuf_create(struct miscdevice *device,
 		ret = -ENOMEM;
 		goto err;
 	}
+	ubuf->offsets = kcalloc(ubuf->pagecount, sizeof(*ubuf->offsets),
+				GFP_KERNEL);
+	if (!ubuf->offsets) {
+		ret = -ENOMEM;
+		goto err;
+	}
 
 	pgbuf = 0;
 	for (i = 0; i < head->count; i++) {
 		ret = -EBADFD;
 		memfd = fget(list[i].memfd);
 		if (!memfd)
 			goto err;
-		mapping = memfd->f_mapping;
-		if (!shmem_mapping(mapping))
+		if (!shmem_file(memfd) && !is_file_hugepages(memfd))
 			goto err;
 		seals = memfd_fcntl(memfd, F_GET_SEALS, 0);
 		if (seals == -EINVAL)
@@ -251,16 +327,19 @@ static long udmabuf_create(struct miscdevice *device,
 		if ((seals & SEALS_WANTED) != SEALS_WANTED ||
 		    (seals & SEALS_DENIED) != 0)
 			goto err;
-		pgoff = list[i].offset >> PAGE_SHIFT;
-		pgcnt = list[i].size   >> PAGE_SHIFT;
-		for (pgidx = 0; pgidx < pgcnt; pgidx++) {
-			page = shmem_read_mapping_page(mapping, pgoff + pgidx);
-			if (IS_ERR(page)) {
-				ret = PTR_ERR(page);
-				goto err;
-			}
-			ubuf->pages[pgbuf++] = page;
-		}
+
+		pgcnt = list[i].size >> PAGE_SHIFT;
+		if (is_file_hugepages(memfd))
+			ret = handle_hugetlb_pages(ubuf, memfd,
+						   list[i].offset,
+						   pgcnt, &pgbuf);
+		else
+			ret = handle_shmem_pages(ubuf, memfd,
+						 list[i].offset,
+						 pgcnt, &pgbuf);
+		if (ret < 0)
+			goto err;
+
 		fput(memfd);
 		memfd = NULL;
 	}
@@ -287,6 +366,7 @@ static long udmabuf_create(struct miscdevice *device,
 		put_page(ubuf->pages[--pgbuf]);
 	if (memfd)
 		fput(memfd);
+	kfree(ubuf->offsets);
 	kfree(ubuf->pages);
 	kfree(ubuf);
 	return ret;