[PATCH 19/20] drm/xe/vm: Support for adding null page VMA to VM on request

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

From: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>

The XE2 (and PVC) HW has a limitation that the pagefault due to invalid
access will halt the corresponding EUs. So, in order to activate the
debugger, kmd needs to install the temporal page to unhalt the EUs.
Plan to be used for pagefault handling when the EU debugger is running.
The idea is to install a null page vma if the pagefault is from an invalid
access. After installing null page pte, the user debugger can continue to
run/inspect without causing a fatal failure or reset and stop.
Based on Bruce's implementation [1].

[1] https://lore.kernel.org/intel-xe/20230829231648.4438-1-yu.bruce.chang@intel.com/

Cc: Oak Zeng <oak.zeng@intel.com>
Cc: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Cc: Stuart Summers <stuart.summers@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Co-developed-by: Bruce Chang <yu.bruce.chang@intel.com>
Signed-off-by: Bruce Chang <yu.bruce.chang@intel.com>
Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
---
 drivers/gpu/drm/xe/xe_vm.c | 33 +++++++++++++++++++++++++++++++++
 drivers/gpu/drm/xe/xe_vm.h |  2 ++
 2 files changed, 35 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
index 5a05563009b2..444ef151431a 100644
--- a/drivers/gpu/drm/xe/xe_vm.c
+++ b/drivers/gpu/drm/xe/xe_vm.c
@@ -4534,3 +4534,36 @@ int xe_vm_alloc_cpu_addr_mirror_vma(struct xe_vm *vm, uint64_t start, uint64_t r
 
 	return xe_vm_alloc_vma(vm, &map_req, false);
 }
+
+struct xe_vma *xe_vm_create_null_vma(struct xe_vm *vm, u64 addr)
+{
+	struct xe_vma_mem_attr default_attr = {
+		.preferred_loc = {
+			.devmem_fd = DRM_XE_PREFERRED_LOC_DEFAULT_DEVICE,
+			.migration_policy = DRM_XE_MIGRATE_ALL_PAGES,
+		},
+		.atomic_access = DRM_XE_ATOMIC_UNDEFINED,
+		.default_pat_index = vm->xe->pat.idx[XE_CACHE_NONE],
+		.pat_index = vm->xe->pat.idx[XE_CACHE_NONE],
+	};
+	struct xe_vma *vma;
+	u32 page_size;
+	int err;
+
+	if (xe_vm_is_closed_or_banned(vm))
+		return ERR_PTR(-ENOENT);
+
+	page_size = vm->flags & XE_VM_FLAG_64K ? SZ_64K : SZ_4K;
+	vma = xe_vma_create(vm, NULL, 0, addr, addr + page_size - 1,
+			    &default_attr, VMA_CREATE_FLAG_IS_NULL);
+	if (IS_ERR_OR_NULL(vma))
+		return vma;
+
+	err = xe_vm_insert_vma(vm, vma);
+	if (err) {
+		xe_vma_destroy_late(vma);
+		return ERR_PTR(err);
+	}
+
+	return vma;
+}
diff --git a/drivers/gpu/drm/xe/xe_vm.h b/drivers/gpu/drm/xe/xe_vm.h
index ef8a5019574e..ebaaa855e231 100644
--- a/drivers/gpu/drm/xe/xe_vm.h
+++ b/drivers/gpu/drm/xe/xe_vm.h
@@ -411,4 +411,6 @@ static inline struct drm_exec *xe_vm_validation_exec(struct xe_vm *vm)
 #define xe_vm_has_valid_gpu_mapping(tile, tile_present, tile_invalidated)	\
 	((READ_ONCE(tile_present) & ~READ_ONCE(tile_invalidated)) & BIT((tile)->id))
 
+struct xe_vma *xe_vm_create_null_vma(struct xe_vm *vm, u64 addr);
+
 #endif
-- 
2.43.0