[PATCH v2 2/2] udmabuf: Add back support for mapping hugetlb pages (v2)

[Vivek Kasireddy <vivek.kasireddy@intel.com>]

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.

v2: Updated get_sg_table() to manually populate the scatterlist for
    both huge page and non-huge-page cases.

Cc: David Hildenbrand <david@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Dongwon Kim <dongwon.kim@intel.com>
Cc: Junxiao Chang <junxiao.chang@intel.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
---
 drivers/dma-buf/udmabuf.c | 84 +++++++++++++++++++++++++++++++++------
 1 file changed, 71 insertions(+), 13 deletions(-)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index 820c993c8659..10c47bf77fb5 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/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 +43,10 @@ static vm_fault_t udmabuf_vm_fault(struct vm_fault *vmf)
 		return VM_FAULT_SIGBUS;
 
 	pfn = page_to_pfn(ubuf->pages[pgoff]);
+	if (ubuf->offsets) {
+		pfn += ubuf->offsets[pgoff] >> PAGE_SHIFT;
+	}
+
 	return vmf_insert_pfn(vma, vmf->address, pfn);
 }
 
@@ -90,23 +96,31 @@ 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;
+	pgoff_t offset;
+	unsigned long 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) {
+		offset = ubuf->offsets ? ubuf->offsets[i] : 0;
+		sg_set_page(sgl, ubuf->pages[i], PAGE_SIZE, offset);
+	}
 	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 +157,7 @@ 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);
 }
@@ -206,7 +221,9 @@ static long udmabuf_create(struct miscdevice *device,
 	struct udmabuf *ubuf;
 	struct dma_buf *buf;
 	pgoff_t pgoff, pgcnt, pgidx, pgbuf = 0, pglimit;
-	struct page *page;
+	struct page *page, *hpage = NULL;
+	pgoff_t hpoff, chunkoff, maxchunks;
+	struct hstate *hpstate;
 	int seals, ret = -EINVAL;
 	u32 i, flags;
 
@@ -242,7 +259,7 @@ static long udmabuf_create(struct miscdevice *device,
 		if (!memfd)
 			goto err;
 		mapping = memfd->f_mapping;
-		if (!shmem_mapping(mapping))
+		if (!shmem_mapping(mapping) && !is_file_hugepages(memfd))
 			goto err;
 		seals = memfd_fcntl(memfd, F_GET_SEALS, 0);
 		if (seals == -EINVAL)
@@ -253,16 +270,56 @@ static long udmabuf_create(struct miscdevice *device,
 			goto err;
 		pgoff = list[i].offset >> PAGE_SHIFT;
 		pgcnt = list[i].size   >> PAGE_SHIFT;
+		if (is_file_hugepages(memfd)) {
+			if (!ubuf->offsets) {
+				ubuf->offsets = kmalloc_array(ubuf->pagecount,
+							      sizeof(*ubuf->offsets),
+							      GFP_KERNEL);
+				if (!ubuf->offsets) {
+					ret = -ENOMEM;
+					goto err;
+				}
+			}
+			hpstate = hstate_file(memfd);
+			hpoff = list[i].offset >> huge_page_shift(hpstate);
+			chunkoff = (list[i].offset &
+				    ~huge_page_mask(hpstate)) >> PAGE_SHIFT;
+			maxchunks = huge_page_size(hpstate) >> 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;
+			if (is_file_hugepages(memfd)) {
+				if (!hpage) {
+					hpage = find_get_page_flags(mapping, hpoff,
+								    FGP_ACCESSED);
+					if (!hpage) {
+						ret = -EINVAL;
+						goto err;
+					}
+				}
+				get_page(hpage);
+				ubuf->pages[pgbuf] = hpage;
+				ubuf->offsets[pgbuf++] = chunkoff << PAGE_SHIFT;
+				if (++chunkoff == maxchunks) {
+					put_page(hpage);
+					hpage = NULL;
+					chunkoff = 0;
+					hpoff++;
+				}
+			} else {
+				page = shmem_read_mapping_page(mapping, pgoff + pgidx);
+				if (IS_ERR(page)) {
+					ret = PTR_ERR(page);
+					goto err;
+				}
+				ubuf->pages[pgbuf++] = page;
 			}
-			ubuf->pages[pgbuf++] = page;
 		}
 		fput(memfd);
 		memfd = NULL;
+		if (hpage) {
+			put_page(hpage);
+			hpage = NULL;
+		}
 	}
 
 	exp_info.ops  = &udmabuf_ops;
@@ -287,6 +344,7 @@ 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;
-- 
2.39.2