Changes in trace_remote.c

e4bf304f000e6fcceaf60b1455a5124b783b3a66 - Merge tag 'trace-ringbuffer-v7.1' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Wed, 15 Apr 2026 22:59:46 +0000

Merge tag 'trace-ringbuffer-v7.1' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracePull ring-buffer updates from Steven Rostedt: - Add remote buffers for pKVM pKVM has a hypervisor component that is used to protect the guest from the host kernel. This hypervisor is a black box to the kernel as the kernel is to user space. The remote buffers are used to have a memory mapping between the hypervisor and the kernel where kernel may send commands to enable tracing within the hypervisor. Then the kernel will read this memory mapping just like user space can read the memory mapped ring buffer of the kernel tracing system. Since the hypervisor only has a single context, it doesn't need to worry about races between normal context, interrupt context and NMIs like the kernel does. The ring buffer it uses doesn't need to be as complex. The remote buffers are a simple version of the ring buffer that works in a single context. They are still per-CPU and use sub buffers. The data layout is the same as the kernel's ring buffer to share the same parsing. Currently, only ARM64 implements pKVM, but there's work to implement it also in x86. The remote buffer code is separated out from the ARM implementation so that it can be used in the future by x86. The ARM64 updates for pKVM is in the ARM/KVM tree and it merged in the remote buffers of this tree. - Make the backup instance non reusable The backup instance is a copy of the persistent ring buffer so that the persistent ring buffer could start recording again without using the data from the previous boot. The backup isn't for normal tracing. It is made read-only, and after it is consumed, it is automatically removed. - Have backup copy persistent instance before it starts recording To allow the persistent ring buffer to start recording from the kernel command line commands, move the copy of the backup instance to before the the command line options start recording. - Report header_page overwrite field as "char" and not "int' The rust parser of the header_page file was triggering a warning when it defined the overwrite variable as "int" but it was only a single byte in size. - Fix memory barriers for the trace_buffer CPU mask When a CPU comes online, the bit is set to allow readers to know that the CPU buffer is allocated. The bit is set after the allocation is done, and a smp_wmb() is performed after the allocation and before the setting of the bit. But instead of adding a smp_rmb() to all readers, since once a buffer is created for a CPU it is not deleted if that CPU goes offline, so this allocation is almost always done at boot up before any readers exist. If for the unlikely case where a CPU comes online for the first time after the system boot has finished, send an IPI to all CPUs to force the smp_rmb() for each CPU. - Show clock function being used in debugging ring buffer data When the ring buffer checks are enabled and the ring buffer detects an inconsistency in the times of the invents, print out the clock being used when the error occurred. There was a very hard to hit bug that would happen every so often and it ended up being only triggered when the jiffies clock was being used. If the bug showed the clock being used, it would have been much easier to find the problem (which was an internal function was being traced which caused the clock accounting to go off).* tag 'trace-ringbuffer-v7.1' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (26 commits) ring-buffer: Prevent off-by-one array access in ring_buffer_desc_page() ring-buffer: Report header_page overwrite as char tracing: Allow backup to save persistent ring buffer before it starts tracing/Documentation: Add a section about backup instance tracing: Remove the backup instance automatically after read tracing: Make the backup instance non-reusable ring-buffer: Enforce read ordering of trace_buffer cpumask and buffers ring-buffer: Show what clock function is used on timestamp errors tracing: Check for undefined symbols in simple_ring_buffer tracing: load/unload page callbacks for simple_ring_buffer Documentation: tracing: Add tracing remotes tracing: selftests: Add trace remote tests tracing: Add a trace remote module for testing tracing: Introduce simple_ring_buffer ring-buffer: Export buffer_data_page and macros tracing: Add helpers to create trace remote events tracing: Add events/ root files to trace remotes tracing: Add events to trace remotes tracing: Add init callback to trace remotes tracing: Add non-consuming read to trace remotes ... List of files: /linux/kernel/trace/trace_remote.c

775cb093bc50649e83ad00ce5347d6fbd4aa8387 - tracing: Add events/ root files to trace remotes

Mon, 09 Mar 2026 16:24:56 +0000

tracing: Add events/ root files to trace remotesJust like for the kernel events directory, add 'enable', 'header_page'and 'header_event' at the root of the trace remote events/ directory.Link: https://patch.msgid.link/20260309162516.2623589-11-vdonnefort@google.comReviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) List of files: /linux/kernel/trace/trace_remote.c

072529158e604cc964feb78dcf094c6975828146 - tracing: Add events to trace remotes

Mon, 09 Mar 2026 16:24:55 +0000

tracing: Add events to trace remotesAn event is predefined point in the writer code that allows to logdata. Following the same scheme as kernel events, add remote events,described to user-space within the events/ tracefs directory found inthe corresponding trace remote.Remote events are expected to be described during the trace remoteregistration.Add also a .enable_event callback for trace_remote to toggle the eventlogging, if supported.Link: https://patch.msgid.link/20260309162516.2623589-10-vdonnefort@google.comReviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) List of files: /linux/kernel/trace/trace_remote.c

bf2ba0f8ca1af14aaaa765cbb93caf564d383aad - tracing: Add init callback to trace remotes

Mon, 09 Mar 2026 16:24:54 +0000

tracing: Add init callback to trace remotesAdd a .init call back so the trace remote callers can add entries to thetracefs directory.Link: https://patch.msgid.link/20260309162516.2623589-9-vdonnefort@google.comReviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) List of files: /linux/kernel/trace/trace_remote.c

330b0cceb30634864d1e9c661eb5524c52d70c07 - tracing: Add non-consuming read to trace remotes

Mon, 09 Mar 2026 16:24:53 +0000

tracing: Add non-consuming read to trace remotesAllow reading the trace file for trace remotes. This performs anon-consuming read of the trace buffer.Link: https://patch.msgid.link/20260309162516.2623589-8-vdonnefort@google.comReviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) List of files: /linux/kernel/trace/trace_remote.c

9af4ab0e11e336e2671d303ffcc6578e3546d9fc - tracing: Add reset to trace remotes

Mon, 09 Mar 2026 16:24:52 +0000

tracing: Add reset to trace remotesAllow to reset the trace remote buffer by writing to the Tracefs "trace"file. This is similar to the regular Tracefs interface.Link: https://patch.msgid.link/20260309162516.2623589-7-vdonnefort@google.comReviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) List of files: /linux/kernel/trace/trace_remote.c

96e43537af5461b26f50904c6055046ba65d742f - tracing: Introduce trace remotes

Mon, 09 Mar 2026 16:24:51 +0000

tracing: Introduce trace remotesA trace remote relies on ring-buffer remotes to read and controlcompatible tracing buffers, written by entity such as firmware orhypervisor.Add a Tracefs directory remotes/ that contains all instances of traceremotes. Each instance follows the same hierarchy as any other to easethe support by existing user-space tools.This currently does not provide any event support, which will comelater.Link: https://patch.msgid.link/20260309162516.2623589-6-vdonnefort@google.comReviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) List of files: /linux/kernel/trace/trace_remote.c