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 --- .../admin-guide/device-mapper/statistics.rst | 225 +++++++++++++++++++++ 1 file changed, 225 insertions(+) create mode 100644 Documentation/admin-guide/device-mapper/statistics.rst (limited to 'Documentation/admin-guide/device-mapper/statistics.rst') diff --git a/Documentation/admin-guide/device-mapper/statistics.rst b/Documentation/admin-guide/device-mapper/statistics.rst new file mode 100644 index 000000000..41ded0bc5 --- /dev/null +++ b/Documentation/admin-guide/device-mapper/statistics.rst @@ -0,0 +1,225 @@ +============= +DM statistics +============= + +Device Mapper supports the collection of I/O statistics on user-defined +regions of a DM device. If no regions are defined no statistics are +collected so there isn't any performance impact. Only bio-based DM +devices are currently supported. + +Each user-defined region specifies a starting sector, length and step. +Individual statistics will be collected for each step-sized area within +the range specified. + +The I/O statistics counters for each step-sized area of a region are +in the same format as `/sys/block/*/stat` or `/proc/diskstats` (see: +Documentation/admin-guide/iostats.rst). But two extra counters (12 and 13) are +provided: total time spent reading and writing. When the histogram +argument is used, the 14th parameter is reported that represents the +histogram of latencies. All these counters may be accessed by sending +the @stats_print message to the appropriate DM device via dmsetup. + +The reported times are in milliseconds and the granularity depends on +the kernel ticks. When the option precise_timestamps is used, the +reported times are in nanoseconds. + +Each region has a corresponding unique identifier, which we call a +region_id, that is assigned when the region is created. The region_id +must be supplied when querying statistics about the region, deleting the +region, etc. Unique region_ids enable multiple userspace programs to +request and process statistics for the same DM device without stepping +on each other's data. + +The creation of DM statistics will allocate memory via kmalloc or +fallback to using vmalloc space. At most, 1/4 of the overall system +memory may be allocated by DM statistics. The admin can see how much +memory is used by reading: + + /sys/module/dm_mod/parameters/stats_current_allocated_bytes + +Messages +======== + + @stats_create [ ...] [ []] + Create a new region and return the region_id. + + + "-" + whole device + "+" + a range of 512-byte sectors + starting with . + + + "" + the range is subdivided into areas each containing + sectors. + "/" + the range is subdivided into the specified + number of areas. + + + The number of optional arguments + + + The following optional arguments are supported: + + precise_timestamps + use precise timer with nanosecond resolution + instead of the "jiffies" variable. When this argument is + used, the resulting times are in nanoseconds instead of + milliseconds. Precise timestamps are a little bit slower + to obtain than jiffies-based timestamps. + histogram:n1,n2,n3,n4,... + collect histogram of latencies. The + numbers n1, n2, etc are times that represent the boundaries + of the histogram. If precise_timestamps is not used, the + times are in milliseconds, otherwise they are in + nanoseconds. For each range, the kernel will report the + number of requests that completed within this range. For + example, if we use "histogram:10,20,30", the kernel will + report four numbers a:b:c:d. a is the number of requests + that took 0-10 ms to complete, b is the number of requests + that took 10-20 ms to complete, c is the number of requests + that took 20-30 ms to complete and d is the number of + requests that took more than 30 ms to complete. + + + An optional parameter. A name that uniquely identifies + the userspace owner of the range. This groups ranges together + so that userspace programs can identify the ranges they + created and ignore those created by others. + The kernel returns this string back in the output of + @stats_list message, but it doesn't use it for anything else. + If we omit the number of optional arguments, program id must not + be a number, otherwise it would be interpreted as the number of + optional arguments. + + + An optional parameter. A word that provides auxiliary data + that is useful to the client program that created the range. + The kernel returns this string back in the output of + @stats_list message, but it doesn't use this value for anything. + + @stats_delete + Delete the region with the specified id. + + + region_id returned from @stats_create + + @stats_clear + Clear all the counters except the in-flight i/o counters. + + + region_id returned from @stats_create + + @stats_list [] + List all regions registered with @stats_create. + + + An optional parameter. + If this parameter is specified, only matching regions + are returned. + If it is not specified, all regions are returned. + + Output format: + : + + precise_timestamps histogram:n1,n2,n3,... + + The strings "precise_timestamps" and "histogram" are printed only + if they were specified when creating the region. + + @stats_print [ ] + Print counters for each step-sized area of a region. + + + region_id returned from @stats_create + + + The index of the starting line in the output. + If omitted, all lines are returned. + + + The number of lines to include in the output. + If omitted, all lines are returned. + + Output format for each step-sized area of a region: + + + + counters + + The first 11 counters have the same meaning as + `/sys/block/*/stat or /proc/diskstats`. + + Please refer to Documentation/admin-guide/iostats.rst for details. + + 1. the number of reads completed + 2. the number of reads merged + 3. the number of sectors read + 4. the number of milliseconds spent reading + 5. the number of writes completed + 6. the number of writes merged + 7. the number of sectors written + 8. the number of milliseconds spent writing + 9. the number of I/Os currently in progress + 10. the number of milliseconds spent doing I/Os + 11. the weighted number of milliseconds spent doing I/Os + + Additional counters: + + 12. the total time spent reading in milliseconds + 13. the total time spent writing in milliseconds + + @stats_print_clear [ ] + Atomically print and then clear all the counters except the + in-flight i/o counters. Useful when the client consuming the + statistics does not want to lose any statistics (those updated + between printing and clearing). + + + region_id returned from @stats_create + + + The index of the starting line in the output. + If omitted, all lines are printed and then cleared. + + + The number of lines to process. + If omitted, all lines are printed and then cleared. + + @stats_set_aux + Store auxiliary data aux_data for the specified region. + + + region_id returned from @stats_create + + + The string that identifies data which is useful to the client + program that created the range. The kernel returns this + string back in the output of @stats_list message, but it + doesn't use this value for anything. + +Examples +======== + +Subdivide the DM device 'vol' into 100 pieces and start collecting +statistics on them:: + + dmsetup message vol 0 @stats_create - /100 + +Set the auxiliary data string to "foo bar baz" (the escape for each +space must also be escaped, otherwise the shell will consume them):: + + dmsetup message vol 0 @stats_set_aux 0 foo\\ bar\\ baz + +List the statistics:: + + dmsetup message vol 0 @stats_list + +Print the statistics:: + + dmsetup message vol 0 @stats_print 0 + +Delete the statistics:: + + dmsetup message vol 0 @stats_delete 0 -- cgit v1.3.1