Changes in simple_ring_buffer.c

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

Thu, 16 Apr 2026 00:59:46 +0200

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/simple_ring_buffer.c

e74c3a8891c05f88eeb87121de7e12dc95766a4a - Merge tag 'kvmarm-7.1' of git://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm into HEAD

Mon, 13 Apr 2026 11:49:54 +0200

Merge tag 'kvmarm-7.1' of git://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm into HEADKVM/arm64 updates for 7.1* New features:- Add support for tracing in the standalone EL2 hypervisor code, which should help both debugging and performance analysis. This comes with a full infrastructure for 'remote' trace buffers that can be exposed by non-kernel entities such as firmware.- Add support for GICv5 Per Processor Interrupts (PPIs), as the starting point for supporting the new GIC architecture in KVM.- Finally add support for pKVM protected guests, with anonymous memory being used as a backing store. About time!* Improvements and bug fixes:- Rework the dreaded user_mem_abort() function to make it more maintainable, reducing the amount of state being exposed to the various helpers and rendering a substantial amount of state immutable.- Expand the Stage-2 page table dumper to support NV shadow page tables on a per-VM basis.- Tidy up the pKVM PSCI proxy code to be slightly less hard to follow.- Fix both SPE and TRBE in non-VHE configurations so that they do not generate spurious, out of context table walks that ultimately lead to very bad HW lockups.- A small set of patches fixing the Stage-2 MMU freeing in error cases.- Tighten-up accepted SMC immediate value to be only #0 for host SMCCC calls.- The usual cleanups and other selftest churn. List of files: /linux/kernel/trace/simple_ring_buffer.c

2de32a25a3f721052c9aaf753a65b96f63c2c7d9 - Merge branch kvm-arm64/hyp-tracing into kvmarm-master/next

Wed, 08 Apr 2026 13:21:51 +0200

Merge branch kvm-arm64/hyp-tracing into kvmarm-master/next* kvm-arm64/hyp-tracing: (40 commits) : . : EL2 tracing support, adding both 'remote' ring-buffer : infrastructure and the tracing itself, courtesy of : Vincent Donnefort. From the cover letter: : : "The growing set of features supported by the hypervisor in protected : mode necessitates debugging and profiling tools. Tracefs is the : ideal candidate for this task: : : * It is simple to use and to script. : : * It is supported by various tools, from the trace-cmd CLI to the : Android web-based perfetto. : : * The ring-buffer, where are stored trace events consists of linked : pages, making it an ideal structure for sharing between kernel and : hypervisor. : : This series first introduces a new generic way of creating remote events and : remote buffers. Then it adds support to the pKVM hypervisor." : . tracing: selftests: Extend hotplug testing for trace remotes tracing: Non-consuming read for trace remotes with an offline CPU tracing: Adjust cmd_check_undefined to show unexpected undefined symbols tracing: Restore accidentally removed SPDX tag KVM: arm64: avoid unused-variable warning tracing: Generate undef symbols allowlist for simple_ring_buffer KVM: arm64: tracing: add ftrace dependency tracing: add more symbols to whitelist tracing: Update undefined symbols allow list for simple_ring_buffer KVM: arm64: Fix out-of-tree build for nVHE/pKVM tracing tracing: selftests: Add hypervisor trace remote tests KVM: arm64: Add selftest event support to nVHE/pKVM hyp KVM: arm64: Add hyp_enter/hyp_exit events to nVHE/pKVM hyp KVM: arm64: Add event support to the nVHE/pKVM hyp and trace remote KVM: arm64: Add trace reset to the nVHE/pKVM hyp KVM: arm64: Sync boot clock with the nVHE/pKVM hyp KVM: arm64: Add trace remote for the nVHE/pKVM hyp KVM: arm64: Add tracing capability for the nVHE/pKVM hyp KVM: arm64: Support unaligned fixmap in the pKVM hyp KVM: arm64: Initialise hyp_nr_cpus for nVHE hyp ...Signed-off-by: Marc Zyngier List of files: /linux/kernel/trace/simple_ring_buffer.c

635923081c792c830fb87e680d6dd5f348926b3f - tracing: load/unload page callbacks for simple_ring_buffer

Mon, 09 Mar 2026 17:25:03 +0100

tracing: load/unload page callbacks for simple_ring_bufferAdd load/unload callback used for each admitted page in the ring-buffer.This will be later useful for the pKVM hypervisor which uses a differentVA space and need to dynamically map/unmap the ring-buffer pages.Link: https://patch.msgid.link/20260309162516.2623589-18-vdonnefort@google.comReviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) List of files: /linux/kernel/trace/simple_ring_buffer.c

34e5b958bdad0f9cf16306368bbc2dc5b2a50143 - tracing: Introduce simple_ring_buffer

Mon, 09 Mar 2026 17:24:59 +0100

tracing: Introduce simple_ring_bufferAdd a simple implementation of the kernel ring-buffer. This intends tobe used later by ring-buffer remotes such as the pKVM hypervisor, hencethe need for a cut down version (write only) without any dependency.Link: https://patch.msgid.link/20260309162516.2623589-14-vdonnefort@google.comReviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) List of files: /linux/kernel/trace/simple_ring_buffer.c