[PATCH 1/2] drm: Ask whether drm_gem_get_pages() should clear the CPU cache
Chris Wilson
chris at chris-wilson.co.uk
Mon Oct 12 10:51:30 UTC 2020
On some processors (such as arch/x86), accessing a page via a WC PAT is
bypassed if the page is physically tagged in the CPU cache, and the
access is serviced by the cache instead -- which leads to incoherency
should the physical page itself be accessed using DMA. In order to
prevent the false cache sharing of the physical pages, we need to
explicitly flush the cache lines of those pages.
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
drivers/gpu/drm/drm_gem.c | 8 ++++++--
drivers/gpu/drm/drm_gem_shmem_helper.c | 8 +++++++-
drivers/gpu/drm/etnaviv/etnaviv_gem.c | 2 +-
drivers/gpu/drm/gma500/gtt.c | 2 +-
drivers/gpu/drm/msm/msm_gem.c | 2 +-
drivers/gpu/drm/omapdrm/omap_gem.c | 2 +-
drivers/gpu/drm/rockchip/rockchip_drm_gem.c | 2 +-
drivers/gpu/drm/tegra/gem.c | 2 +-
drivers/gpu/drm/vgem/vgem_drv.c | 2 +-
drivers/gpu/drm/vkms/vkms_gem.c | 2 +-
drivers/gpu/drm/xen/xen_drm_front_gem.c | 2 +-
include/drm/drm_gem.h | 2 +-
12 files changed, 23 insertions(+), 13 deletions(-)
diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index 1da67d34e55d..1948855d69e6 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -40,6 +40,7 @@
#include <linux/pagevec.h>
#include <drm/drm.h>
+#include <drm/drm_cache.h>
#include <drm/drm_device.h>
#include <drm/drm_drv.h>
#include <drm/drm_file.h>
@@ -525,6 +526,7 @@ static void drm_gem_check_release_pagevec(struct pagevec *pvec)
* drm_gem_get_pages - helper to allocate backing pages for a GEM object
* from shmem
* @obj: obj in question
+ * @clflush: whether to clear any CPU caches associated with the backing store
*
* This reads the page-array of the shmem-backing storage of the given gem
* object. An array of pages is returned. If a page is not allocated or
@@ -546,14 +548,13 @@ static void drm_gem_check_release_pagevec(struct pagevec *pvec)
* drm_gem_object_init(), but not for those initialized with
* drm_gem_private_object_init() only.
*/
-struct page **drm_gem_get_pages(struct drm_gem_object *obj)
+struct page **drm_gem_get_pages(struct drm_gem_object *obj, bool clflush)
{
struct address_space *mapping;
struct page *p, **pages;
struct pagevec pvec;
int i, npages;
-
if (WARN_ON(!obj->filp))
return ERR_PTR(-EINVAL);
@@ -589,6 +590,9 @@ struct page **drm_gem_get_pages(struct drm_gem_object *obj)
(page_to_pfn(p) >= 0x00100000UL));
}
+ if (clflush)
+ drm_clflush_pages(pages, npages);
+
return pages;
fail:
diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index fb11df7aced5..78a2eb77802b 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -152,7 +152,13 @@ static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem)
if (shmem->pages_use_count++ > 0)
return 0;
- pages = drm_gem_get_pages(obj);
+ /*
+ * On some processors (such as arch/x86), accessing a page via a WC PAT
+ * is bypassed if the page is physically tagged in the CPU cache, and
+ * the access is serviced by the cache instead -- which leads to
+ * incoherency should the physical page itself be accessed using DMA.
+ */
+ pages = drm_gem_get_pages(obj, !shmem->map_cached);
if (IS_ERR(pages)) {
DRM_DEBUG_KMS("Failed to get pages (%ld)\n", PTR_ERR(pages));
shmem->pages_use_count = 0;
diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
index 67d9a2b9ea6a..d8279ea363b3 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c
+++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
@@ -58,7 +58,7 @@ static void etnaviv_gem_scatterlist_unmap(struct etnaviv_gem_object *etnaviv_obj
static int etnaviv_gem_shmem_get_pages(struct etnaviv_gem_object *etnaviv_obj)
{
struct drm_device *dev = etnaviv_obj->base.dev;
- struct page **p = drm_gem_get_pages(&etnaviv_obj->base);
+ struct page **p = drm_gem_get_pages(&etnaviv_obj->base, false);
if (IS_ERR(p)) {
dev_dbg(dev->dev, "could not get pages: %ld\n", PTR_ERR(p));
diff --git a/drivers/gpu/drm/gma500/gtt.c b/drivers/gpu/drm/gma500/gtt.c
index 9278bcfad1bf..ada56aec7e68 100644
--- a/drivers/gpu/drm/gma500/gtt.c
+++ b/drivers/gpu/drm/gma500/gtt.c
@@ -197,7 +197,7 @@ static int psb_gtt_attach_pages(struct gtt_range *gt)
WARN_ON(gt->pages);
- pages = drm_gem_get_pages(>->gem);
+ pages = drm_gem_get_pages(>->gem, false);
if (IS_ERR(pages))
return PTR_ERR(pages);
diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index c79828d31822..a7a67ef4e27e 100644
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -102,7 +102,7 @@ static struct page **get_pages(struct drm_gem_object *obj)
int npages = obj->size >> PAGE_SHIFT;
if (use_pages(obj))
- p = drm_gem_get_pages(obj);
+ p = drm_gem_get_pages(obj, false);
else
p = get_pages_vram(obj, npages);
diff --git a/drivers/gpu/drm/omapdrm/omap_gem.c b/drivers/gpu/drm/omapdrm/omap_gem.c
index d8e09792793a..1ff272c4be33 100644
--- a/drivers/gpu/drm/omapdrm/omap_gem.c
+++ b/drivers/gpu/drm/omapdrm/omap_gem.c
@@ -236,7 +236,7 @@ static int omap_gem_attach_pages(struct drm_gem_object *obj)
if (!(omap_obj->flags & OMAP_BO_MEM_SHMEM) || omap_obj->pages)
return 0;
- pages = drm_gem_get_pages(obj);
+ pages = drm_gem_get_pages(obj, false);
if (IS_ERR(pages)) {
dev_err(obj->dev->dev, "could not get pages: %ld\n", PTR_ERR(pages));
return PTR_ERR(pages);
diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
index 7d5ebb10323b..003b76c3e623 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
@@ -80,7 +80,7 @@ static int rockchip_gem_get_pages(struct rockchip_gem_object *rk_obj)
int ret, i;
struct scatterlist *s;
- rk_obj->pages = drm_gem_get_pages(&rk_obj->base);
+ rk_obj->pages = drm_gem_get_pages(&rk_obj->base, false);
if (IS_ERR(rk_obj->pages))
return PTR_ERR(rk_obj->pages);
diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
index 26af8daa9a16..f075f005ecbb 100644
--- a/drivers/gpu/drm/tegra/gem.c
+++ b/drivers/gpu/drm/tegra/gem.c
@@ -289,7 +289,7 @@ static int tegra_bo_get_pages(struct drm_device *drm, struct tegra_bo *bo)
{
int err;
- bo->pages = drm_gem_get_pages(&bo->gem);
+ bo->pages = drm_gem_get_pages(&bo->gem, false);
if (IS_ERR(bo->pages))
return PTR_ERR(bo->pages);
diff --git a/drivers/gpu/drm/vgem/vgem_drv.c b/drivers/gpu/drm/vgem/vgem_drv.c
index fa54a6d1403d..f38dd590fa45 100644
--- a/drivers/gpu/drm/vgem/vgem_drv.c
+++ b/drivers/gpu/drm/vgem/vgem_drv.c
@@ -272,7 +272,7 @@ static struct page **vgem_pin_pages(struct drm_vgem_gem_object *bo)
if (bo->pages_pin_count++ == 0) {
struct page **pages;
- pages = drm_gem_get_pages(&bo->base);
+ pages = drm_gem_get_pages(&bo->base, false);
if (IS_ERR(pages)) {
bo->pages_pin_count--;
mutex_unlock(&bo->pages_lock);
diff --git a/drivers/gpu/drm/vkms/vkms_gem.c b/drivers/gpu/drm/vkms/vkms_gem.c
index 19a0e260a4df..1d17b0ef56c7 100644
--- a/drivers/gpu/drm/vkms/vkms_gem.c
+++ b/drivers/gpu/drm/vkms/vkms_gem.c
@@ -166,7 +166,7 @@ static struct page **_get_pages(struct vkms_gem_object *vkms_obj)
struct drm_gem_object *gem_obj = &vkms_obj->gem;
if (!vkms_obj->pages) {
- struct page **pages = drm_gem_get_pages(gem_obj);
+ struct page **pages = drm_gem_get_pages(gem_obj, false);
if (IS_ERR(pages))
return pages;
diff --git a/drivers/gpu/drm/xen/xen_drm_front_gem.c b/drivers/gpu/drm/xen/xen_drm_front_gem.c
index 4f34ef34ba60..520a15d75eb6 100644
--- a/drivers/gpu/drm/xen/xen_drm_front_gem.c
+++ b/drivers/gpu/drm/xen/xen_drm_front_gem.c
@@ -132,7 +132,7 @@ static struct xen_gem_object *gem_create(struct drm_device *dev, size_t size)
* with the backend
*/
xen_obj->num_pages = DIV_ROUND_UP(size, PAGE_SIZE);
- xen_obj->pages = drm_gem_get_pages(&xen_obj->base);
+ xen_obj->pages = drm_gem_get_pages(&xen_obj->base, false);
if (IS_ERR(xen_obj->pages)) {
ret = PTR_ERR(xen_obj->pages);
xen_obj->pages = NULL;
diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
index c38dd35da00b..118f13b1bb29 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -395,7 +395,7 @@ void drm_gem_free_mmap_offset(struct drm_gem_object *obj);
int drm_gem_create_mmap_offset(struct drm_gem_object *obj);
int drm_gem_create_mmap_offset_size(struct drm_gem_object *obj, size_t size);
-struct page **drm_gem_get_pages(struct drm_gem_object *obj);
+struct page **drm_gem_get_pages(struct drm_gem_object *obj, bool clflush);
void drm_gem_put_pages(struct drm_gem_object *obj, struct page **pages,
bool dirty, bool accessed);
--
2.20.1
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