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Subject[PATCH 4.13 28/47] drm/vgem: Pin our pages for dmabuf exports
Date
4.13-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Chris Wilson <chris@chris-wilson.co.uk>

commit 71bb23c707c141b176bc084179ca5ee58d5fd26a upstream.

When the caller maps their dmabuf and we return an sg_table, the caller
doesn't expect the pages beneath that sg_table to vanish on a whim (i.e.
under mempressure). The contract is that the pages are pinned for the
duration of the mapping (from dma_buf_map_attachment() to
dma_buf_unmap_attachment). To comply, we need to introduce our own
vgem_object.pages_pin_count and elevate it across the mapping. However,
the drm_prime interface we use calls drv->prime_pin on dma_buf_attach
and drv->prime_unpin on dma_buf_detach, which while that does cover the
mapping is much broader than is desired -- but it will do for now.

v2: also hold the pin across prime_vmap/vunmap

Reported-by: Tomi Sarvela <tomi.p.sarvela@intel.com>
Testcase: igt/gem_concurrent_blit/*swap*vgem*
Fixes: 5ba6c9ff961a ("drm/vgem: Fix mmaping")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tomi Sarvela <tomi.p.sarvela@intel.com>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: <stable@vger.kernel.org> # needs a backport
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20170622134617.17912-1-chris@chris-wilson.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/gpu/drm/vgem/vgem_drv.c | 81 +++++++++++++++++++++++++++++-----------
drivers/gpu/drm/vgem/vgem_drv.h | 4 +
2 files changed, 64 insertions(+), 21 deletions(-)

--- a/drivers/gpu/drm/vgem/vgem_drv.c
+++ b/drivers/gpu/drm/vgem/vgem_drv.c
@@ -52,6 +52,7 @@ static void vgem_gem_free_object(struct
struct drm_vgem_gem_object *vgem_obj = to_vgem_bo(obj);

kvfree(vgem_obj->pages);
+ mutex_destroy(&vgem_obj->pages_lock);

if (obj->import_attach)
drm_prime_gem_destroy(obj, vgem_obj->table);
@@ -76,11 +77,15 @@ static int vgem_gem_fault(struct vm_faul
if (page_offset > num_pages)
return VM_FAULT_SIGBUS;

+ ret = -ENOENT;
+ mutex_lock(&obj->pages_lock);
if (obj->pages) {
get_page(obj->pages[page_offset]);
vmf->page = obj->pages[page_offset];
ret = 0;
- } else {
+ }
+ mutex_unlock(&obj->pages_lock);
+ if (ret) {
struct page *page;

page = shmem_read_mapping_page(
@@ -161,6 +166,8 @@ static struct drm_vgem_gem_object *__vge
return ERR_PTR(ret);
}

+ mutex_init(&obj->pages_lock);
+
return obj;
}

@@ -274,37 +281,66 @@ static const struct file_operations vgem
.release = drm_release,
};

+static struct page **vgem_pin_pages(struct drm_vgem_gem_object *bo)
+{
+ mutex_lock(&bo->pages_lock);
+ if (bo->pages_pin_count++ == 0) {
+ struct page **pages;
+
+ pages = drm_gem_get_pages(&bo->base);
+ if (IS_ERR(pages)) {
+ bo->pages_pin_count--;
+ mutex_unlock(&bo->pages_lock);
+ return pages;
+ }
+
+ bo->pages = pages;
+ }
+ mutex_unlock(&bo->pages_lock);
+
+ return bo->pages;
+}
+
+static void vgem_unpin_pages(struct drm_vgem_gem_object *bo)
+{
+ mutex_lock(&bo->pages_lock);
+ if (--bo->pages_pin_count == 0) {
+ drm_gem_put_pages(&bo->base, bo->pages, true, true);
+ bo->pages = NULL;
+ }
+ mutex_unlock(&bo->pages_lock);
+}
+
static int vgem_prime_pin(struct drm_gem_object *obj)
{
+ struct drm_vgem_gem_object *bo = to_vgem_bo(obj);
long n_pages = obj->size >> PAGE_SHIFT;
struct page **pages;

- /* Flush the object from the CPU cache so that importers can rely
- * on coherent indirect access via the exported dma-address.
- */
- pages = drm_gem_get_pages(obj);
+ pages = vgem_pin_pages(bo);
if (IS_ERR(pages))
return PTR_ERR(pages);

+ /* Flush the object from the CPU cache so that importers can rely
+ * on coherent indirect access via the exported dma-address.
+ */
drm_clflush_pages(pages, n_pages);
- drm_gem_put_pages(obj, pages, true, false);

return 0;
}

-static struct sg_table *vgem_prime_get_sg_table(struct drm_gem_object *obj)
+static void vgem_prime_unpin(struct drm_gem_object *obj)
{
- struct sg_table *st;
- struct page **pages;
+ struct drm_vgem_gem_object *bo = to_vgem_bo(obj);

- pages = drm_gem_get_pages(obj);
- if (IS_ERR(pages))
- return ERR_CAST(pages);
+ vgem_unpin_pages(bo);
+}

- st = drm_prime_pages_to_sg(pages, obj->size >> PAGE_SHIFT);
- drm_gem_put_pages(obj, pages, false, false);
+static struct sg_table *vgem_prime_get_sg_table(struct drm_gem_object *obj)
+{
+ struct drm_vgem_gem_object *bo = to_vgem_bo(obj);

- return st;
+ return drm_prime_pages_to_sg(bo->pages, bo->base.size >> PAGE_SHIFT);
}

static struct drm_gem_object* vgem_prime_import(struct drm_device *dev,
@@ -333,6 +369,8 @@ static struct drm_gem_object *vgem_prime
__vgem_gem_destroy(obj);
return ERR_PTR(-ENOMEM);
}
+
+ obj->pages_pin_count++; /* perma-pinned */
drm_prime_sg_to_page_addr_arrays(obj->table, obj->pages, NULL,
npages);
return &obj->base;
@@ -340,23 +378,23 @@ static struct drm_gem_object *vgem_prime

static void *vgem_prime_vmap(struct drm_gem_object *obj)
{
+ struct drm_vgem_gem_object *bo = to_vgem_bo(obj);
long n_pages = obj->size >> PAGE_SHIFT;
struct page **pages;
- void *addr;

- pages = drm_gem_get_pages(obj);
+ pages = vgem_pin_pages(bo);
if (IS_ERR(pages))
return NULL;

- addr = vmap(pages, n_pages, 0, pgprot_writecombine(PAGE_KERNEL));
- drm_gem_put_pages(obj, pages, false, false);
-
- return addr;
+ return vmap(pages, n_pages, 0, pgprot_writecombine(PAGE_KERNEL));
}

static void vgem_prime_vunmap(struct drm_gem_object *obj, void *vaddr)
{
+ struct drm_vgem_gem_object *bo = to_vgem_bo(obj);
+
vunmap(vaddr);
+ vgem_unpin_pages(bo);
}

static int vgem_prime_mmap(struct drm_gem_object *obj,
@@ -409,6 +447,7 @@ static struct drm_driver vgem_driver = {
.prime_handle_to_fd = drm_gem_prime_handle_to_fd,
.prime_fd_to_handle = drm_gem_prime_fd_to_handle,
.gem_prime_pin = vgem_prime_pin,
+ .gem_prime_unpin = vgem_prime_unpin,
.gem_prime_import = vgem_prime_import,
.gem_prime_export = drm_gem_prime_export,
.gem_prime_import_sg_table = vgem_prime_import_sg_table,
--- a/drivers/gpu/drm/vgem/vgem_drv.h
+++ b/drivers/gpu/drm/vgem/vgem_drv.h
@@ -43,7 +43,11 @@ struct vgem_file {
#define to_vgem_bo(x) container_of(x, struct drm_vgem_gem_object, base)
struct drm_vgem_gem_object {
struct drm_gem_object base;
+
struct page **pages;
+ unsigned int pages_pin_count;
+ struct mutex pages_lock;
+
struct sg_table *table;
};


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