[PATCH] udmabuf: Add support for mapping hugepages

[PATCH] udmabuf: Add support for mapping hugepages

[Vivek Kasireddy]

If the VMM's (Qemu) memory backend is backed up by memfd + Hugepages
(hugetlbfs and not THP), we have to first find the hugepage(s) where
the Guest allocations are located and then extract the regular 4k
sized subpages from them.

Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
---
 drivers/dma-buf/udmabuf.c | 40 +++++++++++++++++++++++++++++++--------
 1 file changed, 32 insertions(+), 8 deletions(-)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index db732f71e59a..4a976a56cbc3 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -11,6 +11,7 @@
 #include <linux/shmem_fs.h>
 #include <linux/slab.h>
 #include <linux/udmabuf.h>
+#include <linux/hugetlb.h>
 
 static const u32    list_limit = 1024;  /* udmabuf_create_list->count limit */
 static const size_t size_limit_mb = 64; /* total dmabuf size, in megabytes  */
@@ -162,8 +163,9 @@ static long udmabuf_create(struct miscdevice *device,
 	struct file *memfd = NULL;
 	struct udmabuf *ubuf;
 	struct dma_buf *buf;
-	pgoff_t pgoff, pgcnt, pgidx, pgbuf = 0, pglimit;
-	struct page *page;
+	pgoff_t pgoff, pgcnt, pgidx, pgbuf = 0, pglimit, subpgoff;
+	struct page *page, *hpage = NULL;
+	struct hstate *hpstate;
 	int seals, ret = -EINVAL;
 	u32 i, flags;
 
@@ -194,7 +196,8 @@ static long udmabuf_create(struct miscdevice *device,
 		memfd = fget(list[i].memfd);
 		if (!memfd)
 			goto err;
-		if (!shmem_mapping(file_inode(memfd)->i_mapping))
+		if (!shmem_mapping(file_inode(memfd)->i_mapping) &&
+		    !is_file_hugepages(memfd))
 			goto err;
 		seals = memfd_fcntl(memfd, F_GET_SEALS, 0);
 		if (seals == -EINVAL)
@@ -205,17 +208,38 @@ static long udmabuf_create(struct miscdevice *device,
 			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(
-				file_inode(memfd)->i_mapping, pgoff + pgidx);
-			if (IS_ERR(page)) {
-				ret = PTR_ERR(page);
+		if (is_file_hugepages(memfd)) {
+			hpstate = hstate_file(memfd);
+			pgoff = list[i].offset >> huge_page_shift(hpstate);
+			subpgoff = (list[i].offset &
+				    ~huge_page_mask(hpstate)) >> PAGE_SHIFT;
+			hpage = find_get_page_flags(
+					file_inode(memfd)->i_mapping,
+					pgoff, FGP_ACCESSED);
+			if (IS_ERR(hpage)) {
+				ret = PTR_ERR(hpage);
 				goto err;
 			}
+		}
+		for (pgidx = 0; pgidx < pgcnt; pgidx++) {
+			if (is_file_hugepages(memfd)) {
+				page = hpage + subpgoff + pgidx;
+				get_page(page);
+			} else {
+				page = shmem_read_mapping_page(
+					file_inode(memfd)->i_mapping,
+					pgoff + pgidx);
+				if (IS_ERR(page)) {
+					ret = PTR_ERR(page);
+					goto err;
+				}
+			}
 			ubuf->pages[pgbuf++] = page;
 		}
 		fput(memfd);
 		memfd = NULL;
+		if (hpage)
+			put_page(hpage);
 	}
 
 	exp_info.ops  = &udmabuf_ops;
-- 
2.30.2

Re: [PATCH] udmabuf: Add support for mapping hugepages

[Gerd Hoffmann]

  Hi,

> +		if (is_file_hugepages(memfd)) {
> +			hpstate = hstate_file(memfd);
> +			pgoff = list[i].offset >> huge_page_shift(hpstate);
> +			subpgoff = (list[i].offset &
> +				    ~huge_page_mask(hpstate)) >> PAGE_SHIFT;
> +			hpage = find_get_page_flags(
> +					file_inode(memfd)->i_mapping,
> +					pgoff, FGP_ACCESSED);
> +			if (IS_ERR(hpage)) {
> +				ret = PTR_ERR(hpage);
>  				goto err;
>  			}
> +		}
> +		for (pgidx = 0; pgidx < pgcnt; pgidx++) {
> +			if (is_file_hugepages(memfd)) {
> +				page = hpage + subpgoff + pgidx;
> +				get_page(page);

Hmm.  Does this work in case the page range spans multiple huge pages?

take care,
  Gerd

[PATCH] udmabuf: Add support for mapping hugepages (v2)

[Vivek Kasireddy]

If the VMM's (Qemu) memory backend is backed up by memfd + Hugepages
(hugetlbfs and not THP), we have to first find the hugepage(s) where
the Guest allocations are located and then extract the regular 4k
sized subpages from them.

v2: Ensure that the subpage offsets are calculated correctly when the
range of subpage allocations cuts across multiple hugepages.

Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
---
 drivers/dma-buf/udmabuf.c | 46 ++++++++++++++++++++++++++++++++-------
 1 file changed, 38 insertions(+), 8 deletions(-)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index db732f71e59a..f053d12a1eb3 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -11,6 +11,7 @@
 #include <linux/shmem_fs.h>
 #include <linux/slab.h>
 #include <linux/udmabuf.h>
+#include <linux/hugetlb.h>
 
 static const u32    list_limit = 1024;  /* udmabuf_create_list->count limit */
 static const size_t size_limit_mb = 64; /* total dmabuf size, in megabytes  */
@@ -162,8 +163,10 @@ static long udmabuf_create(struct miscdevice *device,
 	struct file *memfd = NULL;
 	struct udmabuf *ubuf;
 	struct dma_buf *buf;
-	pgoff_t pgoff, pgcnt, pgidx, pgbuf = 0, pglimit;
-	struct page *page;
+	pgoff_t pgoff, pgcnt, pgidx, pgbuf = 0, pglimit, subpgoff;
+	uint32_t maxsubpgs;
+	struct page *page, *hpage = NULL;
+	struct hstate *hpstate;
 	int seals, ret = -EINVAL;
 	u32 i, flags;
 
@@ -194,7 +197,8 @@ static long udmabuf_create(struct miscdevice *device,
 		memfd = fget(list[i].memfd);
 		if (!memfd)
 			goto err;
-		if (!shmem_mapping(file_inode(memfd)->i_mapping))
+		if (!shmem_mapping(file_inode(memfd)->i_mapping) &&
+		    !is_file_hugepages(memfd))
 			goto err;
 		seals = memfd_fcntl(memfd, F_GET_SEALS, 0);
 		if (seals == -EINVAL)
@@ -205,12 +209,38 @@ 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)) {
+			hpstate = hstate_file(memfd);
+			pgoff = list[i].offset >> huge_page_shift(hpstate);
+			subpgoff = (list[i].offset &
+				    ~huge_page_mask(hpstate)) >> PAGE_SHIFT;
+			maxsubpgs = huge_page_size(hpstate) >> PAGE_SHIFT;
+		}
 		for (pgidx = 0; pgidx < pgcnt; pgidx++) {
-			page = shmem_read_mapping_page(
-				file_inode(memfd)->i_mapping, pgoff + pgidx);
-			if (IS_ERR(page)) {
-				ret = PTR_ERR(page);
-				goto err;
+			if (is_file_hugepages(memfd)) {
+				hpage = find_get_page_flags(
+						file_inode(memfd)->i_mapping,
+						pgoff, FGP_ACCESSED);
+				if (IS_ERR(hpage)) {
+					ret = PTR_ERR(hpage);
+					goto err;
+				}
+
+				page = hpage + (subpgoff % maxsubpgs);
+				get_page(page);
+				put_page(hpage);
+
+				subpgoff++;
+				if (subpgoff % maxsubpgs == 0)
+					pgoff++;
+			} else {
+				page = shmem_read_mapping_page(
+					file_inode(memfd)->i_mapping,
+					pgoff + pgidx);
+				if (IS_ERR(page)) {
+					ret = PTR_ERR(page);
+					goto err;
+				}
 			}
 			ubuf->pages[pgbuf++] = page;
 		}
-- 
2.30.2

Re: [PATCH] udmabuf: Add support for mapping hugepages (v2)

[Gerd Hoffmann]

  Hi,

>  		for (pgidx = 0; pgidx < pgcnt; pgidx++) {
> +			if (is_file_hugepages(memfd)) {
> +				hpage = find_get_page_flags(
> +						file_inode(memfd)->i_mapping,
> +						pgoff, FGP_ACCESSED);
> +				if (IS_ERR(hpage)) {
> +					ret = PTR_ERR(hpage);
> +					goto err;
> +				}
> +
> +				page = hpage + (subpgoff % maxsubpgs);
> +				get_page(page);
> +				put_page(hpage);

if (hpage && subpgoff == maxsubpgs) {
	put_page(hpage);
	hpage = NULL;
}
if (!hpage) {
	hpage = find_get_page_flags(...)
	[ ... ]
}

Only lookup the huge page when you cross a hugepage border.

take care,
  Gerd

[PATCH] udmabuf: Add support for mapping hugepages (v3)

[Vivek Kasireddy]

If the VMM's (Qemu) memory backend is backed up by memfd + Hugepages
(hugetlbfs and not THP), we have to first find the hugepage(s) where
the Guest allocations are located and then extract the regular 4k
sized subpages from them.

v2: Ensure that the subpage and hugepage offsets are calculated correctly
when the range of subpage allocations cuts across multiple hugepages.

v3: Instead of repeatedly looking up the hugepage for each subpage,
only do it when the subpage allocation crosses over into a different
hugepage. (suggested by Gerd and DW)

Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Signed-off-by: Dongwon Kim <dongwon.kim@intel.com>
---
 drivers/dma-buf/udmabuf.c | 51 +++++++++++++++++++++++++++++++++------
 1 file changed, 44 insertions(+), 7 deletions(-)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index db732f71e59a..2e02bbfe30fd 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -11,6 +11,7 @@
 #include <linux/shmem_fs.h>
 #include <linux/slab.h>
 #include <linux/udmabuf.h>
+#include <linux/hugetlb.h>
 
 static const u32    list_limit = 1024;  /* udmabuf_create_list->count limit */
 static const size_t size_limit_mb = 64; /* total dmabuf size, in megabytes  */
@@ -163,7 +164,9 @@ 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 subpgoff, maxsubpgs;
+	struct hstate *hpstate;
 	int seals, ret = -EINVAL;
 	u32 i, flags;
 
@@ -194,7 +197,8 @@ static long udmabuf_create(struct miscdevice *device,
 		memfd = fget(list[i].memfd);
 		if (!memfd)
 			goto err;
-		if (!shmem_mapping(file_inode(memfd)->i_mapping))
+		if (!shmem_mapping(file_inode(memfd)->i_mapping) &&
+		    !is_file_hugepages(memfd))
 			goto err;
 		seals = memfd_fcntl(memfd, F_GET_SEALS, 0);
 		if (seals == -EINVAL)
@@ -205,17 +209,50 @@ 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)) {
+			hpstate = hstate_file(memfd);
+			pgoff = list[i].offset >> huge_page_shift(hpstate);
+			subpgoff = (list[i].offset &
+				    ~huge_page_mask(hpstate)) >> PAGE_SHIFT;
+			maxsubpgs = huge_page_size(hpstate) >> PAGE_SHIFT;
+		}
 		for (pgidx = 0; pgidx < pgcnt; pgidx++) {
-			page = shmem_read_mapping_page(
-				file_inode(memfd)->i_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(
+						file_inode(memfd)->i_mapping,
+						pgoff, FGP_ACCESSED);
+					if (IS_ERR(hpage)) {
+						ret = PTR_ERR(hpage);
+						goto err;
+					}
+				}
+				page = hpage + subpgoff;
+				get_page(page);
+				subpgoff++;
+				if (subpgoff == maxsubpgs) {
+					put_page(hpage);
+					hpage = NULL;
+					subpgoff = 0;
+					pgoff++;
+				}
+			} else {
+				page = shmem_read_mapping_page(
+					file_inode(memfd)->i_mapping,
+					pgoff + pgidx);
+				if (IS_ERR(page)) {
+					ret = PTR_ERR(page);
+					goto err;
+				}
 			}
 			ubuf->pages[pgbuf++] = page;
 		}
 		fput(memfd);
 		memfd = NULL;
+		if (hpage) {
+			put_page(hpage);
+			hpage = NULL;
+		}
 	}
 
 	exp_info.ops  = &udmabuf_ops;
-- 
2.30.2

Re: [PATCH] udmabuf: Add support for mapping hugepages (v3)

[Dongwon Kim]

I see the number of entries in the list often exceeds list_limit
currently hardcoded to 1024 for full HD scanout resource (==
1920*1080*4 bytes). Can we include a change to increase it to something
like 4096 or higher in this patch?

On Fri, Jun 04, 2021 at 01:59:39PM -0700, Vivek Kasireddy wrote:
> If the VMM's (Qemu) memory backend is backed up by memfd + Hugepages
> (hugetlbfs and not THP), we have to first find the hugepage(s) where
> the Guest allocations are located and then extract the regular 4k
> sized subpages from them.
> 
> v2: Ensure that the subpage and hugepage offsets are calculated correctly
> when the range of subpage allocations cuts across multiple hugepages.
> 
> v3: Instead of repeatedly looking up the hugepage for each subpage,
> only do it when the subpage allocation crosses over into a different
> hugepage. (suggested by Gerd and DW)
> 
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
> Signed-off-by: Dongwon Kim <dongwon.kim@intel.com>
> ---
>  drivers/dma-buf/udmabuf.c | 51 +++++++++++++++++++++++++++++++++------
>  1 file changed, 44 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> index db732f71e59a..2e02bbfe30fd 100644
> --- a/drivers/dma-buf/udmabuf.c
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -11,6 +11,7 @@
>  #include <linux/shmem_fs.h>
>  #include <linux/slab.h>
>  #include <linux/udmabuf.h>
> +#include <linux/hugetlb.h>
>  
>  static const u32    list_limit = 1024;  /* udmabuf_create_list->count limit */
>  static const size_t size_limit_mb = 64; /* total dmabuf size, in megabytes  */
> @@ -163,7 +164,9 @@ 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 subpgoff, maxsubpgs;
> +	struct hstate *hpstate;
>  	int seals, ret = -EINVAL;
>  	u32 i, flags;
>  
> @@ -194,7 +197,8 @@ static long udmabuf_create(struct miscdevice *device,
>  		memfd = fget(list[i].memfd);
>  		if (!memfd)
>  			goto err;
> -		if (!shmem_mapping(file_inode(memfd)->i_mapping))
> +		if (!shmem_mapping(file_inode(memfd)->i_mapping) &&
> +		    !is_file_hugepages(memfd))
>  			goto err;
>  		seals = memfd_fcntl(memfd, F_GET_SEALS, 0);
>  		if (seals == -EINVAL)
> @@ -205,17 +209,50 @@ 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)) {
> +			hpstate = hstate_file(memfd);
> +			pgoff = list[i].offset >> huge_page_shift(hpstate);
> +			subpgoff = (list[i].offset &
> +				    ~huge_page_mask(hpstate)) >> PAGE_SHIFT;
> +			maxsubpgs = huge_page_size(hpstate) >> PAGE_SHIFT;
> +		}
>  		for (pgidx = 0; pgidx < pgcnt; pgidx++) {
> -			page = shmem_read_mapping_page(
> -				file_inode(memfd)->i_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(
> +						file_inode(memfd)->i_mapping,
> +						pgoff, FGP_ACCESSED);
> +					if (IS_ERR(hpage)) {
> +						ret = PTR_ERR(hpage);
> +						goto err;
> +					}
> +				}
> +				page = hpage + subpgoff;
> +				get_page(page);
> +				subpgoff++;
> +				if (subpgoff == maxsubpgs) {
> +					put_page(hpage);
> +					hpage = NULL;
> +					subpgoff = 0;
> +					pgoff++;
> +				}
> +			} else {
> +				page = shmem_read_mapping_page(
> +					file_inode(memfd)->i_mapping,
> +					pgoff + pgidx);
> +				if (IS_ERR(page)) {
> +					ret = PTR_ERR(page);
> +					goto err;
> +				}
>  			}
>  			ubuf->pages[pgbuf++] = page;
>  		}
>  		fput(memfd);
>  		memfd = NULL;
> +		if (hpage) {
> +			put_page(hpage);
> +			hpage = NULL;
> +		}
>  	}
>  
>  	exp_info.ops  = &udmabuf_ops;
> -- 
> 2.30.2
> 

Re: [PATCH] udmabuf: Add support for mapping hugepages (v3)

[Gerd Hoffmann]

On Tue, Jun 08, 2021 at 10:35:58AM -0700, Dongwon Kim wrote:
> I see the number of entries in the list often exceeds list_limit
> currently hardcoded to 1024 for full HD scanout resource (==
> 1920*1080*4 bytes). Can we include a change to increase it to something
> like 4096 or higher in this patch?

Separate patch please (and maybe turn limits into module parameters
while being at it).

take care,
  Gerd

Re: [PATCH] udmabuf: Add support for mapping hugepages (v3)

[Gerd Hoffmann]

  Hi,

> +					hpage = find_get_page_flags(

checkpatch doesn't like that:

-:76: CHECK:OPEN_ENDED_LINE: Lines should not end with a '('

> +				page = shmem_read_mapping_page(

Same here.

take care,
  Gerd

[PATCH] udmabuf: Add support for mapping hugepages (v4)

[Vivek Kasireddy]

If the VMM's (Qemu) memory backend is backed up by memfd + Hugepages
(hugetlbfs and not THP), we have to first find the hugepage(s) where
the Guest allocations are located and then extract the regular 4k
sized subpages from them.

v2: Ensure that the subpage and hugepage offsets are calculated correctly
when the range of subpage allocations cuts across multiple hugepages.

v3: Instead of repeatedly looking up the hugepage for each subpage,
only do it when the subpage allocation crosses over into a different
hugepage. (suggested by Gerd and DW)

v4: Fix the following warning identified by checkpatch:
CHECK:OPEN_ENDED_LINE: Lines should not end with a '('

Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Signed-off-by: Dongwon Kim <dongwon.kim@intel.com>
---
 drivers/dma-buf/udmabuf.c | 50 +++++++++++++++++++++++++++++++++------
 1 file changed, 43 insertions(+), 7 deletions(-)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index db732f71e59a..d509f0d60794 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -11,6 +11,7 @@
 #include <linux/shmem_fs.h>
 #include <linux/slab.h>
 #include <linux/udmabuf.h>
+#include <linux/hugetlb.h>
 
 static const u32    list_limit = 1024;  /* udmabuf_create_list->count limit */
 static const size_t size_limit_mb = 64; /* total dmabuf size, in megabytes  */
@@ -160,10 +161,13 @@ static long udmabuf_create(struct miscdevice *device,
 {
 	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;
+	struct page *page, *hpage = NULL;
+	pgoff_t subpgoff, maxsubpgs;
+	struct hstate *hpstate;
 	int seals, ret = -EINVAL;
 	u32 i, flags;
 
@@ -194,7 +198,8 @@ static long udmabuf_create(struct miscdevice *device,
 		memfd = fget(list[i].memfd);
 		if (!memfd)
 			goto err;
-		if (!shmem_mapping(file_inode(memfd)->i_mapping))
+		mapping = file_inode(memfd)->i_mapping;
+		if (!shmem_mapping(mapping) && !is_file_hugepages(memfd))
 			goto err;
 		seals = memfd_fcntl(memfd, F_GET_SEALS, 0);
 		if (seals == -EINVAL)
@@ -205,17 +210,48 @@ 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)) {
+			hpstate = hstate_file(memfd);
+			pgoff = list[i].offset >> huge_page_shift(hpstate);
+			subpgoff = (list[i].offset &
+				    ~huge_page_mask(hpstate)) >> PAGE_SHIFT;
+			maxsubpgs = huge_page_size(hpstate) >> PAGE_SHIFT;
+		}
 		for (pgidx = 0; pgidx < pgcnt; pgidx++) {
-			page = shmem_read_mapping_page(
-				file_inode(memfd)->i_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,
+							pgoff, FGP_ACCESSED);
+					if (IS_ERR(hpage)) {
+						ret = PTR_ERR(hpage);
+						goto err;
+					}
+				}
+				page = hpage + subpgoff;
+				get_page(page);
+				subpgoff++;
+				if (subpgoff == maxsubpgs) {
+					put_page(hpage);
+					hpage = NULL;
+					subpgoff = 0;
+					pgoff++;
+				}
+			} else {
+				page = shmem_read_mapping_page(mapping,
+							       pgoff + pgidx);
+				if (IS_ERR(page)) {
+					ret = PTR_ERR(page);
+					goto err;
+				}
 			}
 			ubuf->pages[pgbuf++] = page;
 		}
 		fput(memfd);
 		memfd = NULL;
+		if (hpage) {
+			put_page(hpage);
+			hpage = NULL;
+		}
 	}
 
 	exp_info.ops  = &udmabuf_ops;
-- 
2.30.2

Re: [PATCH] udmabuf: Add support for mapping hugepages (v4)

[Gerd Hoffmann]

On Wed, Jun 09, 2021 at 11:29:15AM -0700, Vivek Kasireddy wrote:
> If the VMM's (Qemu) memory backend is backed up by memfd + Hugepages
> (hugetlbfs and not THP), we have to first find the hugepage(s) where
> the Guest allocations are located and then extract the regular 4k
> sized subpages from them.
> 
> v2: Ensure that the subpage and hugepage offsets are calculated correctly
> when the range of subpage allocations cuts across multiple hugepages.
> 
> v3: Instead of repeatedly looking up the hugepage for each subpage,
> only do it when the subpage allocation crosses over into a different
> hugepage. (suggested by Gerd and DW)
> 
> v4: Fix the following warning identified by checkpatch:
> CHECK:OPEN_ENDED_LINE: Lines should not end with a '('
> 
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
> Signed-off-by: Dongwon Kim <dongwon.kim@intel.com>

> +					hpage = find_get_page_flags(mapping,
> +							pgoff, FGP_ACCESSED);

checkpatch is still not happy.  Fixed that up & pushed to drm-misc-next.

thanks,
  Gerd