From a5f7a5bb3b7f28ba7e4fa246775b29a0e5537255 Mon Sep 17 00:00:00 2001 From: Jinke Han Date: Tue, 8 Sep 2026 15:37:42 +0800 Subject: x86/kprobes: Fix crash when probing CS CALL instructions When using eBPF to probe CS CALL instructions within a function, a crash can be triggered. The eBPF tool probes offset 257 of the __hrtimer_run_queues() function: <__hrtimer_run_queues+249>: nopl 0x0(%rax,%rax,1) <__hrtimer_run_queues+254>: mov %r14,%rdi <__hrtimer_run_queues+257>: cs call <__x86_indirect_thunk_r12> <__hrtimer_run_queues+263>: mov %eax,%r12d <__hrtimer_run_queues+266>: xchg %ax,%ax <__hrtimer_run_queues+268>: mov %r13,%rdi Which triggers this crash: BUG: unable to handle page fault for address: 00000000000f41c9 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page PGD 0 P4D 0 Oops: 0002 [#1] SMP NOPTI CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P RIP: 0010:__hrtimer_run_queues+0x106/0x230 Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is at the 6th byte of the above CS CALL instruction. Since the CS CALL instruction occupies 6 bytes, the exception occurred in the middle of that call instruction. The root cause is that when using eBPF tools to probe in the middle of a function, a kprobe with INT3 is used as the underlying implementation. During single-step emulation of the original CALL instruction, int3_emulate_call() assumes that the probed CALL instruction is 5 bytes long. However, the actual CS-prefixed CALL instruction occupies 6 bytes, so it constructs an incorrect exception return address. When the CPU returns from the kprobe handler, the next instruction to be executed is at the address of the last byte of that CS CALL instruction. Coincidentally, starting from that address, the CPU fetches and decodes a completely different instruction, which ultimately triggers a kernel crash. Fix the issue by using the actual instruction length obtained from the instruction decoder when constructing the exception return address, rather than relying on the hardcoded CALL_INSN_SIZE macro. [ mingo: Refined the changelog ] Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step") Suggested-by: Masami Hiramatsu (Google) Signed-off-by: Jinke Han Signed-off-by: Ingo Molnar Reviewed-by: Masami Hiramatsu (Google) Acked-by: Yafang Shao Acked-by: Borislav Petkov Cc: Peter Zijlstra Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000 --- Documentation/gpu/panthor.rst | 56 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 56 insertions(+) create mode 100644 Documentation/gpu/panthor.rst (limited to 'Documentation/gpu/panthor.rst') diff --git a/Documentation/gpu/panthor.rst b/Documentation/gpu/panthor.rst new file mode 100644 index 000000000..7a8417412 --- /dev/null +++ b/Documentation/gpu/panthor.rst @@ -0,0 +1,56 @@ +.. SPDX-License-Identifier: GPL-2.0+ + +========================= + drm/Panthor CSF driver +========================= + +.. _panthor-usage-stats: + +Panthor DRM client usage stats implementation +============================================== + +The drm/Panthor driver implements the DRM client usage stats specification as +documented in :ref:`drm-client-usage-stats`. + +Example of the output showing the implemented key value pairs and entirety of +the currently possible format options: + +:: + pos: 0 + flags: 02400002 + mnt_id: 29 + ino: 491 + drm-driver: panthor + drm-client-id: 10 + drm-engine-panthor: 111110952750 ns + drm-cycles-panthor: 94439687187 + drm-maxfreq-panthor: 1000000000 Hz + drm-curfreq-panthor: 1000000000 Hz + panthor-resident-memory: 10396 KiB + panthor-active-memory: 10396 KiB + drm-total-memory: 16480 KiB + drm-shared-memory: 0 + drm-active-memory: 16200 KiB + drm-resident-memory: 16480 KiB + drm-purgeable-memory: 0 + +Possible `drm-engine-` key names are: `panthor`. +`drm-curfreq-` values convey the current operating frequency for that engine. + +Users must bear in mind that engine and cycle sampling are disabled by default, +because of power saving concerns. `fdinfo` users and benchmark applications which +query the fdinfo file must make sure to toggle the job profiling status of the +driver by writing into the appropriate sysfs node:: + + echo > /sys/bus/platform/drivers/panthor/[a-f0-9]*.gpu/profiling + +Where `N` is a bit mask where cycle and timestamp sampling are respectively +enabled by the first and second bits. + +Possible `panthor-*-memory` keys are: `active` and `resident`. +These values convey the sizes of the internal driver-owned shmem BO's that +aren't exposed to user-space through a DRM handle, like queue ring buffers, +sync object arrays and heap chunks. Because they are all allocated and pinned +at creation time, only `panthor-resident-memory` is necessary to tell us their +size. `panthor-active-memory` shows the size of kernel BO's associated with +VM's and groups currently being scheduled for execution by the GPU. -- cgit v1.3.1