drm/amdgpu: Surface svm_default_granularity, a RW module parameter

Enables users to update SVM's default granularity, used in
buffer migration and handling of recoverable page faults.
Param value is set in terms of log(numPages(buffer)),
e.g. 9 for a 2 MIB buffer

Signed-off-by: Ramesh Errabolu <Ramesh.Errabolu@amd.com>
Reviewed-by: Philip Yang <Philip.Yang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Author: rerrabolu

drivers/gpu/drm/amd/amdgpu/amdgpu.h

@@ -237,6 +237,7 @@ extern int sched_policy;
 extern bool debug_evictions;
 extern bool no_system_mem_limit;
 extern int halt_if_hws_hang;
+extern uint amdgpu_svm_default_granularity;
 #else
 static const int __maybe_unused sched_policy = KFD_SCHED_POLICY_HWS;
 static const bool __maybe_unused debug_evictions; /* = false */

drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c

@@ -169,6 +169,16 @@ uint amdgpu_sdma_phase_quantum = 32;
 char *amdgpu_disable_cu;
 char *amdgpu_virtual_display;
 bool enforce_isolation;
+
+/* Specifies the default granularity for SVM, used in buffer
+ * migration and restoration of backing memory when handling
+ * recoverable page faults.
+ *
+ * The value is given as log(numPages(buffer)); for a 2 MiB
+ * buffer it computes to be 9
+ */
+uint amdgpu_svm_default_granularity = 9;
+
 /*
  * OverDrive(bit 14) disabled by default
  * GFX DCS(bit 19) disabled by default
@@ -320,6 +330,13 @@ module_param_named(pcie_gen2, amdgpu_pcie_gen2, int, 0444);
 MODULE_PARM_DESC(msi, "MSI support (1 = enable, 0 = disable, -1 = auto)");
 module_param_named(msi, amdgpu_msi, int, 0444);
 
+/**
+ * DOC: svm_default_granularity (uint)
+ * Used in buffer migration and handling of recoverable page faults
+ */
+MODULE_PARM_DESC(svm_default_granularity, "SVM's default granularity in log(2^Pages), default 9 = 2^9 = 2 MiB");
+module_param_named(svm_default_granularity, amdgpu_svm_default_granularity, uint, 0644);
+
 /**
  * DOC: lockup_timeout (string)
  * Set GPU scheduler timeout value in ms.

drivers/gpu/drm/amd/amdkfd/kfd_priv.h

@@ -868,6 +868,12 @@ struct svm_range_list {
 	struct task_struct		*faulting_task;
 	/* check point ts decides if page fault recovery need be dropped */
 	uint64_t			checkpoint_ts[MAX_GPU_INSTANCE];
+
+	/* Default granularity to use in buffer migration
+	 * and restoration of backing memory while handling
+	 * recoverable page faults
+	 */
+	uint8_t default_granularity;
 };
 
 /* Process data */

drivers/gpu/drm/amd/amdkfd/kfd_svm.c

@@ -309,12 +309,13 @@ static void svm_range_free(struct svm_range *prange, bool do_unmap)
 }
 
 static void
-svm_range_set_default_attributes(int32_t *location, int32_t *prefetch_loc,
-				 uint8_t *granularity, uint32_t *flags)
+svm_range_set_default_attributes(struct svm_range_list *svms, int32_t *location,
+				 int32_t *prefetch_loc, uint8_t *granularity,
+				 uint32_t *flags)
 {
 	*location = KFD_IOCTL_SVM_LOCATION_UNDEFINED;
 	*prefetch_loc = KFD_IOCTL_SVM_LOCATION_UNDEFINED;
-	*granularity = 9;
+	*granularity = svms->default_granularity;
 	*flags =
 		KFD_IOCTL_SVM_FLAG_HOST_ACCESS | KFD_IOCTL_SVM_FLAG_COHERENT;
 }
@@ -358,7 +359,7 @@ svm_range *svm_range_new(struct svm_range_list *svms, uint64_t start,
 		bitmap_copy(prange->bitmap_access, svms->bitmap_supported,
 			    MAX_GPU_INSTANCE);
 
-	svm_range_set_default_attributes(&prange->preferred_loc,
+	svm_range_set_default_attributes(svms, &prange->preferred_loc,
 					 &prange->prefetch_loc,
 					 &prange->granularity, &prange->flags);
 
@@ -2703,9 +2704,10 @@ svm_range_get_range_boundaries(struct kfd_process *p, int64_t addr,
 	*is_heap_stack = vma_is_initial_heap(vma) || vma_is_initial_stack(vma);
 
 	start_limit = max(vma->vm_start >> PAGE_SHIFT,
-		      (unsigned long)ALIGN_DOWN(addr, 2UL << 8));
+		      (unsigned long)ALIGN_DOWN(addr, 1UL << p->svms.default_granularity));
 	end_limit = min(vma->vm_end >> PAGE_SHIFT,
-		    (unsigned long)ALIGN(addr + 1, 2UL << 8));
+		    (unsigned long)ALIGN(addr + 1, 1UL << p->svms.default_granularity));
+
 	/* First range that starts after the fault address */
 	node = interval_tree_iter_first(&p->svms.objects, addr + 1, ULONG_MAX);
 	if (node) {
@@ -3249,6 +3251,12 @@ int svm_range_list_init(struct kfd_process *p)
 		if (KFD_IS_SVM_API_SUPPORTED(p->pdds[i]->dev->adev))
 			bitmap_set(svms->bitmap_supported, i, 1);
 
+	 /* Value of default granularity cannot exceed 0x1B, the
+	  * number of pages supported by a 4-level paging table
+	  */
+	svms->default_granularity = min_t(u8, amdgpu_svm_default_granularity, 0x1B);
+	pr_debug("Default SVM Granularity to use: %d\n", svms->default_granularity);
+
 	return 0;
 }
 
@@ -3776,7 +3784,7 @@ svm_range_get_attr(struct kfd_process *p, struct mm_struct *mm,
 	node = interval_tree_iter_first(&svms->objects, start, last);
 	if (!node) {
 		pr_debug("range attrs not found return default values\n");
-		svm_range_set_default_attributes(&location, &prefetch_loc,
+		svm_range_set_default_attributes(svms, &location, &prefetch_loc,
 						 &granularity, &flags_and);
 		flags_or = flags_and;
 		if (p->xnack_enabled)