From b17f0bfdaedda3543723c3d15913a67da8e4c532 Mon Sep 17 00:00:00 2001
From: Matthew Auld <matthew.auld@intel.com>
Date: Mon, 18 Oct 2021 18:45:02 +0100
Subject: drm/i915: extract bypass-llc check into helper
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Git-commit: 30f1dccd295b6865fad9e41873dce2f76998cbae
Patch-mainline: v5.16-rc1
References: jsc#PED-1166 jsc#PED-1168 jsc#PED-1170 jsc#PED-1218 jsc#PED-1220 jsc#PED-1222 jsc#PED-1223 jsc#PED-1225
It looks like we will need this in some more places, so extract as a
helper.
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211018174508.2137279-3-matthew.auld@intel.com
Acked-by: Patrik Jakobsson <pjakobsson@suse.de>
---
drivers/gpu/drm/i915/gem/i915_gem_object.c | 26 ++++++++++++++++++++++
drivers/gpu/drm/i915/gem/i915_gem_object.h | 1 +
drivers/gpu/drm/i915/gem/i915_gem_shmem.c | 17 +-------------
3 files changed, 28 insertions(+), 16 deletions(-)
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c
index 76ce6a1500bc..1e426a42a36c 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_object.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c
@@ -128,6 +128,32 @@ void i915_gem_object_set_cache_coherency(struct drm_i915_gem_object *obj,
!(obj->cache_coherent & I915_BO_CACHE_COHERENT_FOR_WRITE);
}
+bool i915_gem_object_can_bypass_llc(struct drm_i915_gem_object *obj)
+{
+ struct drm_i915_private *i915 = to_i915(obj->base.dev);
+
+ /*
+ * This is purely from a security perspective, so we simply don't care
+ * about non-userspace objects being able to bypass the LLC.
+ */
+ if (!(obj->flags & I915_BO_ALLOC_USER))
+ return false;
+
+ /*
+ * EHL and JSL add the 'Bypass LLC' MOCS entry, which should make it
+ * possible for userspace to bypass the GTT caching bits set by the
+ * kernel, as per the given object cache_level. This is troublesome
+ * since the heavy flush we apply when first gathering the pages is
+ * skipped if the kernel thinks the object is coherent with the GPU. As
+ * a result it might be possible to bypass the cache and read the
+ * contents of the page directly, which could be stale data. If it's
+ * just a case of userspace shooting themselves in the foot then so be
+ * it, but since i915 takes the stance of always zeroing memory before
+ * handing it to userspace, we need to prevent this.
+ */
+ return IS_JSL_EHL(i915);
+}
+
static void i915_gem_close_object(struct drm_gem_object *gem, struct drm_file *file)
{
struct drm_i915_gem_object *obj = to_intel_bo(gem);
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h b/drivers/gpu/drm/i915/gem/i915_gem_object.h
index 9df3ee60604e..59201801cec5 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_object.h
+++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h
@@ -514,6 +514,7 @@ i915_gem_object_finish_access(struct drm_i915_gem_object *obj)
void i915_gem_object_set_cache_coherency(struct drm_i915_gem_object *obj,
unsigned int cache_level);
+bool i915_gem_object_can_bypass_llc(struct drm_i915_gem_object *obj);
void i915_gem_object_flush_if_display(struct drm_i915_gem_object *obj);
void i915_gem_object_flush_if_display_locked(struct drm_i915_gem_object *obj);
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
index 11f072193f3b..cf11aa7e08a0 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
@@ -182,22 +182,7 @@ static int shmem_get_pages(struct drm_i915_gem_object *obj)
if (i915_gem_object_needs_bit17_swizzle(obj))
i915_gem_object_do_bit_17_swizzle(obj, st);
- /*
- * EHL and JSL add the 'Bypass LLC' MOCS entry, which should make it
- * possible for userspace to bypass the GTT caching bits set by the
- * kernel, as per the given object cache_level. This is troublesome
- * since the heavy flush we apply when first gathering the pages is
- * skipped if the kernel thinks the object is coherent with the GPU. As
- * a result it might be possible to bypass the cache and read the
- * contents of the page directly, which could be stale data. If it's
- * just a case of userspace shooting themselves in the foot then so be
- * it, but since i915 takes the stance of always zeroing memory before
- * handing it to userspace, we need to prevent this.
- *
- * By setting cache_dirty here we make the clflush in set_pages
- * unconditional on such platforms.
- */
- if (IS_JSL_EHL(i915) && obj->flags & I915_BO_ALLOC_USER)
+ if (i915_gem_object_can_bypass_llc(obj))
obj->cache_dirty = true;
__i915_gem_object_set_pages(obj, st, sg_page_sizes);
--
2.38.1