| Message ID | 20230718082605.1570740-3-vivek.kasireddy@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | udmabuf: Add back support for mapping hugetlb pages (v2) | expand |
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.
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.
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
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,
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;
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(-)