Re: [PATCH 03/10] drm/i915/uapi: expose the avail tracking

Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx> · Thu, 26 May 2022 08:58:05 +0100

On 25/05/2022 19:43, Matthew Auld wrote:
Vulkan would like to have a rough measure of how much device memory can
in theory be allocated. Also add unallocated_cpu_visible_size to track
the visible portion, in case the device is using small BAR.

I have concerns here that it isn't useful and could even be 
counter-productive. If we give unprivileged access it may be considered 
a side channel, but if we "lie" (report total region size) to 
unprivileged clients (like in this patch), then they don't co-operate 
well and end trashing.

Is Vulkan really sure it wants this and why?

Regards,

Tvrtko

Testcase: igt@i915_query@query-regions-unallocated
Testcase: igt@i915_query@query-regions-sanity-check
Signed-off-by: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
Cc: Lionel Landwerlin <lionel.g.landwerlin@xxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
Cc: Jon Bloomfield <jon.bloomfield@xxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: Jordan Justen <jordan.l.justen@xxxxxxxxx>
Cc: Kenneth Graunke <kenneth@xxxxxxxxxxxxx>
Cc: Akeem G Abodunrin <akeem.g.abodunrin@xxxxxxxxx>
---
  drivers/gpu/drm/i915/i915_query.c             | 10 +++++-
  drivers/gpu/drm/i915/i915_ttm_buddy_manager.c | 20 ++++++++++++
  drivers/gpu/drm/i915/i915_ttm_buddy_manager.h |  3 ++
  drivers/gpu/drm/i915/intel_memory_region.c    | 14 +++++++++
  drivers/gpu/drm/i915/intel_memory_region.h    |  3 ++
  include/uapi/drm/i915_drm.h                   | 31 ++++++++++++++++++-
  6 files changed, 79 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_query.c b/drivers/gpu/drm/i915/i915_query.c
index 9aa0b28aa6ee..e095c55f4d4b 100644
--- a/drivers/gpu/drm/i915/i915_query.c
+++ b/drivers/gpu/drm/i915/i915_query.c
@@ -502,7 +502,15 @@ static int query_memregion_info(struct drm_i915_private *i915,
  		else
  			info.probed_cpu_visible_size = mr->total;
  
-		info.unallocated_size = mr->avail;
+		if (perfmon_capable()) {
+			intel_memory_region_avail(mr,
+						  &info.unallocated_size,
+						  &info.unallocated_cpu_visible_size);
+		} else {
+			info.unallocated_size = info.probed_size;
+			info.unallocated_cpu_visible_size =
+				info.probed_cpu_visible_size;
+		}
  
  		if (__copy_to_user(info_ptr, &info, sizeof(info)))
  			return -EFAULT;
diff --git a/drivers/gpu/drm/i915/i915_ttm_buddy_manager.c b/drivers/gpu/drm/i915/i915_ttm_buddy_manager.c
index a5109548abc0..aa5c91e44438 100644
--- a/drivers/gpu/drm/i915/i915_ttm_buddy_manager.c
+++ b/drivers/gpu/drm/i915/i915_ttm_buddy_manager.c
@@ -365,6 +365,26 @@ u64 i915_ttm_buddy_man_visible_size(struct ttm_resource_manager *man)
  	return bman->visible_size;
  }
  
+/**
+ * i915_ttm_buddy_man_visible_size - Query the avail tracking for the manager.
+ *
+ * @man: The buddy allocator ttm manager
+ * @avail: The total available memory in pages for the entire manager.
+ * @visible_avail: The total available memory in pages for the CPU visible
+ * portion. Note that this will always give the same value as @avail on
+ * configurations that don't have a small BAR.
+ */
+void i915_ttm_buddy_man_avail(struct ttm_resource_manager *man,
+			     u64 *avail, u64 *visible_avail)
+{
+	struct i915_ttm_buddy_manager *bman = to_buddy_manager(man);
+
+	mutex_lock(&bman->lock);
+	*avail = bman->mm.avail >> PAGE_SHIFT;
+	*visible_avail = bman->visible_avail;
+	mutex_unlock(&bman->lock);
+}
+
  #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
  void i915_ttm_buddy_man_force_visible_size(struct ttm_resource_manager *man,
  					   u64 size)
diff --git a/drivers/gpu/drm/i915/i915_ttm_buddy_manager.h b/drivers/gpu/drm/i915/i915_ttm_buddy_manager.h
index 52d9586d242c..d64620712830 100644
--- a/drivers/gpu/drm/i915/i915_ttm_buddy_manager.h
+++ b/drivers/gpu/drm/i915/i915_ttm_buddy_manager.h
@@ -61,6 +61,9 @@ int i915_ttm_buddy_man_reserve(struct ttm_resource_manager *man,
  
  u64 i915_ttm_buddy_man_visible_size(struct ttm_resource_manager *man);
  
+void i915_ttm_buddy_man_avail(struct ttm_resource_manager *man,
+			      u64 *avail, u64 *avail_visible);
+
  #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
  void i915_ttm_buddy_man_force_visible_size(struct ttm_resource_manager *man,
  					   u64 size);
diff --git a/drivers/gpu/drm/i915/intel_memory_region.c b/drivers/gpu/drm/i915/intel_memory_region.c
index e38d2db1c3e3..94ee26e99549 100644
--- a/drivers/gpu/drm/i915/intel_memory_region.c
+++ b/drivers/gpu/drm/i915/intel_memory_region.c
@@ -279,6 +279,20 @@ void intel_memory_region_set_name(struct intel_memory_region *mem,
  	va_end(ap);
  }
  
+void intel_memory_region_avail(struct intel_memory_region *mr,
+			       u64 *avail, u64 *visible_avail)
+{
+	if (mr->type == INTEL_MEMORY_LOCAL) {
+		i915_ttm_buddy_man_avail(mr->region_private,
+					 avail, visible_avail);
+		*avail <<= PAGE_SHIFT;
+		*visible_avail <<= PAGE_SHIFT;
+	} else {
+		*avail = mr->total;
+		*visible_avail = mr->total;
+	}
+}
+
  void intel_memory_region_destroy(struct intel_memory_region *mem)
  {
  	int ret = 0;
diff --git a/drivers/gpu/drm/i915/intel_memory_region.h b/drivers/gpu/drm/i915/intel_memory_region.h
index 3d8378c1b447..2214f251bec3 100644
--- a/drivers/gpu/drm/i915/intel_memory_region.h
+++ b/drivers/gpu/drm/i915/intel_memory_region.h
@@ -127,6 +127,9 @@ int intel_memory_region_reserve(struct intel_memory_region *mem,
  void intel_memory_region_debug(struct intel_memory_region *mr,
  			       struct drm_printer *printer);
  
+void intel_memory_region_avail(struct intel_memory_region *mr,
+			       u64 *avail, u64 *visible_avail);
+
  struct intel_memory_region *
  i915_gem_ttm_system_setup(struct drm_i915_private *i915,
  			  u16 type, u16 instance);
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 9df419a45244..e30f31a440b3 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -3228,7 +3228,15 @@ struct drm_i915_memory_region_info {
  	 */
  	__u64 probed_size;
  
-	/** @unallocated_size: Estimate of memory remaining (-1 = unknown) */
+	/**
+	 * @unallocated_size: Estimate of memory remaining (-1 = unknown)
+	 *
+	 * Requires CAP_PERFMON or CAP_SYS_ADMIN to get reliable accounting.
+	 * Without this (or if this is an older kernel) the value here will
+	 * always equal the @probed_size. Note this is only currently tracked
+	 * for I915_MEMORY_CLASS_DEVICE regions (for other types the value here
+	 * will always equal the @probed_size).
+	 */
  	__u64 unallocated_size;
  
  	union {
@@ -3262,6 +3270,27 @@ struct drm_i915_memory_region_info {
  			 * @probed_size.
  			 */
  			__u64 probed_cpu_visible_size;
+
+			/**
+			 * @unallocated_cpu_visible_size: Estimate of CPU
+			 * visible memory remaining (-1 = unknown).
+			 *
+			 * Note this is only tracked for
+			 * I915_MEMORY_CLASS_DEVICE regions (for other types the
+			 * value here will always equal the
+			 * @probed_cpu_visible_size).
+			 *
+			 * Requires CAP_PERFMON or CAP_SYS_ADMIN to get reliable
+			 * accounting.  Without this the value here will always
+			 * equal the @probed_cpu_visible_size. Note this is only
+			 * currently tracked for I915_MEMORY_CLASS_DEVICE
+			 * regions (for other types the value here will also
+			 * always equal the @probed_cpu_visible_size).
+			 *
+			 * If this is an older kernel the value here will be
+			 * zero, see also @probed_cpu_visible_size.
+			 */
+			__u64 unallocated_cpu_visible_size;
  		};
  	};
  };






