Problem:
While developing the amd_close_race IGT test (which intentionally triggers
execute permission faults by removing VM_PAGE_EXECUTABLE from GPU page table
entries), we discovered that on Navi10 (GFX 10.1.x) these faults produce
zero diagnostic output. The GPU simply hangs silently for ~10s until the
scheduler timeout fires. There is no way to distinguish an execute
permission fault from any other type of GPU hang.
Root cause:
GFX 10.1.x defaults to noretry=0, which sets
RETRY_PERMISSION_OR_INVALID_PAGE_FAULT=1 in the GFXHUB UTCL2 registers
(gfxhub_v2_0.c line 313). With this bit set, permission faults (valid PTE,
wrong R/W/X bits) are handled entirely within the UTCL1/UTCL2 hardware
loop: UTCL2 returns an XNACK to UTCL1, and UTCL1 re-requests the
translation indefinitely, expecting software to eventually fix the
permission bits (as happens in SVM/HMM recovery). No interrupt of any kind
reaches the IH ring.
This is different from invalid-page faults (V=0) which DO generate a retry
fault interrupt that the driver can escalate to a no-retry fault. Permission
faults with valid PTEs loop silently forever in hardware.
GFX 10.3+ already defaults to noretry=1, which makes permission faults
generate immediate L2 protection fault interrupts. GFX 10.1.x was
inadvertently left out of this default.
Fix:
Change the noretry=1 threshold from IP_VERSION(10, 3, 0) to
IP_VERSION(10, 1, 0) in amdgpu_gmc_noretry_set(). This is a one-line
change that aligns GFX 10.1.x behavior with GFX 10.3+ and all newer
generations.
With noretry=1, the existing non-retry fault handler
(gmc_v10_0_process_interrupt) already decodes and prints the full
GCVM_L2_PROTECTION_FAULT_STATUS register including PERMISSION_FAULTS,
faulting address, VMID, PASID, and process name. No additional logging
code is needed — the fix is purely routing permission faults to the
existing, fully-capable non-retry interrupt handler.
v2: Dropped GFX10-specific logging from gmc_v10_0.c and
kfd_int_process_v10.c (Felix Kuehling). v1 added logging in the retry
fault handler, but with noretry=1 permission faults take the non-retry
path — the v1 retry handler code was dead and would never execute.
Tested on Navi10 (GFX 10.1.10):
- Execute permission faults now produce immediate, clear output:
[gfxhub] page fault (src_id:0 ring:64 vmid:4 pasid:592)
Process amd_close_race pid 13380 thread amd_close_race pid 13384
in page at address 0x40001000 from client 0x1b (UTCL2)
GCVM_L2_PROTECTION_FAULT_STATUS:0x00700881
PERMISSION_FAULTS: 0x8
- No regressions with properly-mapped GPU workloads
Cc: Christian Koenig <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Vitaly Prosyak <vitaly.prosyak@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>