[PATCH v2 0/2] udmabuf: Add back support for mapping hugetlb pages (v2)

[PATCH v2 0/2] udmabuf: Add back support for mapping hugetlb pages (v2)

[Vivek Kasireddy]

The first patch ensures that the mappings needed for handling mmap
operation would be managed by using the pfn instead of struct page.
The second patch restores support for mapping hugetlb pages where
subpages of a hugepage are not directly used anymore (main reason
for revert) and instead the hugetlb pages and the relevant offsets
are used to populate the scatterlist for dma-buf export and for
mmap operation.

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 the second patch to manually populate the scatterlist

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>

Vivek Kasireddy (2):
  udmabuf: Use vmf_insert_pfn and VM_PFNMAP for handling mmap
  udmabuf: Add back support for mapping hugetlb pages (v2)

 drivers/dma-buf/udmabuf.c | 92 ++++++++++++++++++++++++++++++++-------
 1 file changed, 76 insertions(+), 16 deletions(-)

-- 
2.39.2

[PATCH v2 1/2] udmabuf: Use vmf_insert_pfn and VM_PFNMAP for handling mmap

[Vivek Kasireddy]

Add VM_PFNMAP to vm_flags in the mmap handler to ensure that
the mappings would be managed without using struct page.

And, in the vm_fault handler, use vmf_insert_pfn to share the
page's pfn to userspace instead of directly sharing the page
(via struct page *).

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>
Suggested-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
---
 drivers/dma-buf/udmabuf.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index c40645999648..820c993c8659 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -35,12 +35,13 @@ static vm_fault_t udmabuf_vm_fault(struct vm_fault *vmf)
 	struct vm_area_struct *vma = vmf->vma;
 	struct udmabuf *ubuf = vma->vm_private_data;
 	pgoff_t pgoff = vmf->pgoff;
+	unsigned long pfn;
 
 	if (pgoff >= ubuf->pagecount)
 		return VM_FAULT_SIGBUS;
-	vmf->page = ubuf->pages[pgoff];
-	get_page(vmf->page);
-	return 0;
+
+	pfn = page_to_pfn(ubuf->pages[pgoff]);
+	return vmf_insert_pfn(vma, vmf->address, pfn);
 }
 
 static const struct vm_operations_struct udmabuf_vm_ops = {
@@ -56,6 +57,7 @@ static int mmap_udmabuf(struct dma_buf *buf, struct vm_area_struct *vma)
 
 	vma->vm_ops = &udmabuf_vm_ops;
 	vma->vm_private_data = ubuf;
+	vm_flags_set(vma, VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP);
 	return 0;
 }
 
-- 
2.39.2

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

[Vivek Kasireddy]

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

Re: [PATCH v2 1/2] udmabuf: Use vmf_insert_pfn and VM_PFNMAP for handling mmap

[David Hildenbrand]

On 18.07.23 10:26, Vivek Kasireddy wrote:
> Add VM_PFNMAP to vm_flags in the mmap handler to ensure that
> the mappings would be managed without using struct page.
> 
> And, in the vm_fault handler, use vmf_insert_pfn to share the
> page's pfn to userspace instead of directly sharing the page
> (via struct page *).
> 
> 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>
> Suggested-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
> ---
>   drivers/dma-buf/udmabuf.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> index c40645999648..820c993c8659 100644
> --- a/drivers/dma-buf/udmabuf.c
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -35,12 +35,13 @@ static vm_fault_t udmabuf_vm_fault(struct vm_fault *vmf)
>   	struct vm_area_struct *vma = vmf->vma;
>   	struct udmabuf *ubuf = vma->vm_private_data;
>   	pgoff_t pgoff = vmf->pgoff;
> +	unsigned long pfn;
>   
>   	if (pgoff >= ubuf->pagecount)
>   		return VM_FAULT_SIGBUS;
> -	vmf->page = ubuf->pages[pgoff];
> -	get_page(vmf->page);
> -	return 0;
> +
> +	pfn = page_to_pfn(ubuf->pages[pgoff]);
> +	return vmf_insert_pfn(vma, vmf->address, pfn);
>   }
>   
>   static const struct vm_operations_struct udmabuf_vm_ops = {
> @@ -56,6 +57,7 @@ static int mmap_udmabuf(struct dma_buf *buf, struct vm_area_struct *vma)
>   
>   	vma->vm_ops = &udmabuf_vm_ops;
>   	vma->vm_private_data = ubuf;
> +	vm_flags_set(vma, VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP);
>   	return 0;
>   }
>   

Looks reasonable to me.

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb

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

[David Hildenbrand]

On 18.07.23 10:26, Vivek Kasireddy wrote:
> 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(-)

LGTM, in general. But I really hope Mike can comment.

-- 
Cheers,

David / dhildenb

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

[Mike Kravetz]

On 07/18/23 01:26, Vivek Kasireddy wrote:
> 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);

Is the intention to increase the ref count of the hugetlb page once for
each 'sub-page' added?  Or, am I reading that incorrectly?

> +				ubuf->pages[pgbuf] = hpage;

Ah!, answering my own question.  Since the 'head page' is added to the
array the ref count of the head page will decremented in
release_udmabuf.

> +				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);

It may not matter to your users, but the semantics for hugetlb and shmem
pages is different.  hugetlb requires the pages exist in the page cache
while shmem will create/add pages to the cache if necessary.

> +				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
> 

Nothing else stands out,

Acked-by: Mike Kravetz <mike.kravetz@oracle.com>

I see there is a RFC for the coherency issue with hole punch.
-- 
Mike Kravetz

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

[Kasireddy, Vivek]

Hi Mike,

> 
> On 07/18/23 01:26, Vivek Kasireddy wrote:
> > 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);
> 
> Is the intention to increase the ref count of the hugetlb page once for
> each 'sub-page' added?  Or, am I reading that incorrectly?
Yes, that's the intention; I figured it makes sense to do it that way.

> 
> > +				ubuf->pages[pgbuf] = hpage;
> 
> Ah!, answering my own question.  Since the 'head page' is added to the
> array the ref count of the head page will decremented in
> release_udmabuf.
Yes, that's right.

> 
> > +				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);
> 
> It may not matter to your users, but the semantics for hugetlb and shmem
> pages is different.  hugetlb requires the pages exist in the page cache
> while shmem will create/add pages to the cache if necessary.
Ok; got it.

> 
> > +				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
> >
> 
> Nothing else stands out,
> 
> Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
Thank you for the quick review!

> 
> I see there is a RFC for the coherency issue with hole punch.
Yes.

Thanks,
Vivek

> --
> Mike Kravetz

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

[Peter Xu]

On Wed, Jul 19, 2023 at 05:42:54AM +0000, Kasireddy, Vivek wrote:
> > > +			} else {
> > > +				page =
> > shmem_read_mapping_page(mapping, pgoff + pgidx);
> > 
> > It may not matter to your users, but the semantics for hugetlb and shmem
> > pages is different.  hugetlb requires the pages exist in the page cache
> > while shmem will create/add pages to the cache if necessary.
> Ok; got it.

Would it be nice to do the same for both (perhaps always try to allocate)?

Thanks,

-- 
Peter Xu