[PATCH 2/2] amd/amdgpu: force to trigger a no-retry-fault after a retry-fault

[Alex Sierra]

Only for the debugger use case.

[why]
Avoid endless translation retries, after an invalid address access has
been issued to the GPU. Instead, the trap handler is forced to enter by
generating a no-retry-fault.
A s_trap instruction is inserted in the debugger case to let the wave to
enter trap handler to save context.

[how]
Intentionally using an invalid flag combination (F and P set at the same
time) to trigger a no-retry-fault, after a retry-fault happens. This is
only valid under compute context.

Change-Id: I4180c30e2631dc0401cbd6171f8a6776e4733c9a
Signed-off-by: Alex Sierra <alex.sierra at amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
index d51ac8771ae0..cd36195ff8be 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
@@ -3202,11 +3202,18 @@ bool amdgpu_vm_handle_fault(struct amdgpu_device *adev, unsigned int pasid,
 	flags = AMDGPU_PTE_VALID | AMDGPU_PTE_SNOOPED |
 		AMDGPU_PTE_SYSTEM;
 
-	if (amdgpu_vm_fault_stop == AMDGPU_VM_FAULT_STOP_NEVER) {
+	if (vm->is_compute_context) {
+		/* Setting PTE flags to trigger a no-retry-fault  */
+		flags = AMDGPU_PTE_EXECUTABLE | AMDGPU_PDE_PTE |
+			AMDGPU_PTE_TF;
+		value = 0;
+
+	} else if (amdgpu_vm_fault_stop == AMDGPU_VM_FAULT_STOP_NEVER) {
 		/* Redirect the access to the dummy page */
 		value = adev->dummy_page_addr;
 		flags |= AMDGPU_PTE_EXECUTABLE | AMDGPU_PTE_READABLE |
 			AMDGPU_PTE_WRITEABLE;
+
 	} else {
 		/* Let the hw retry silently on the PTE */
 		value = 0;
-- 
2.17.1