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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. 1. ring-buffer -------------- To setup the per-cpu ring-buffers, a new interface is created: ring_buffer_remote: Describes what the kernel needs to know about the remote writer, that is, the set of pages forming the ring-buffer and a callback for the reader/head swapping (enables consuming read) ring_buffer_remote(): Creates a read-only ring-buffer from a ring_buffer_remote. To keep the internals of `struct ring_buffer` in sync with the remote, the meta-page is used. It was originally introduced to enable user-space mapping of the ring-buffer [1]. In this case, the kernel is not the producer anymore but the reader. The function to read that meta-page is: ring_buffer_poll_remote(): Update `struct ring_buffer` based on the remote meta-page. Wake-up readers if necessary. The kernel has to poll the meta-page to be notified of newly written events. 2. Tracefs ---------- This series introduce a new trace_remote that does the link between tracefs and the remote ring-buffer. The interface is found in the remotes/ directory at the root of the tracefs mount point. Each remote is like an instance and you'll find there a subset of the regular Tracefs user-space interface: remotes/test/ buffer_size_kb trace_clock trace_pipe trace per_cpu/ cpuX/ trace trace_pipe events/ test/ selftest/ enable id Behind the scenes, kernel/trace/trace_remote.c creates this tracefs hierarchy without relying on kernel/trace/trace.c. This is due to fundamental differences: * Remote tracing doesn't support trace_array's system-specific features (snapshots, tracers, etc.). * Logged event formats differ (e.g., no PID for remote events). * Buffer operations require specific remote interactions. 3. Simple Ring-Buffer --------------------- As the current ring-buffer.c implementation has too many dependencies to be used directly by the pKVM hypervisor. A new simple implementation is created and can be found in kernel/trace/simple-ring-buffer.c. This implementation is write-only and is used by both the pKVM hypervisor and a trace_remote test module. 4. Events --------- A new REMOTE_EVENT() macro is added to simplify the creation of events on the kernel side. As remote tracing buffer are read only, only the event structure and a way of printing must be declared. The prototype of the macro is very similar to the well-known TRACE_EVENT() REMOTE_EVENT(my_event, id, RE_STRUCT( re_field(u64, foobar) ), RE_PRINTK("foobar=%lld", __entry->foobar) ) ) 5. pKVM ------- The pKVM support simply creates a "hypervisor" trace_remote on the kernel side and inherits from simple-ring-buffer.c on the hypervisor side. A new event macro is created HYP_EVENT() that is under the hood re-using REMOTE_EVENT() (defined in the previous paragaph) as well as generate hypervisor specific struct and trace_() functions. 5. Limitations: --------------- Non-consuming reading of the buffer isn't supported (i.e. cat trace -> -EPERM) due to current the lack of support in the ring-buffer meta-page. [1] https://tracingsummit.org/ts/2022/hypervisortracing/ [2] https://lore.kernel.org/all/20240510140435.3550353-1-vdonnefort@google.com/ Changes since v3 (https://lore.kernel.org/all/20250224121353.98697-1-vdonnefort@google.com/) - Move tracefs support from kvm/hyp_trace.c into a generic trace_remote.c. - Move ring-buffer implementation from nvhe/trace.c into a generic simple-ring-buffer.c - Rebase on 6.15-rc4. Changes since v2 (https://lore.kernel.org/all/20250108114536.627715-1-vdonnefort@google.com/) - Fix ring-buffer remote reset - Fix fast-forward in rb_page_desc() - Refactor nvhe/trace.c - struct hyp_buffer_page more compact - Add a struct_len to trace_page_desc - Extend reset testing - Rebase on 6.14-rc3 Changes since v1 (https://lore.kernel.org/all/20240911093029.3279154-1-vdonnefort@google.com/) - Add 128-bits mult fallback in the unlikely event of an overflow. (John) - Fix ELF section sort. - __always_inline trace_* event macros. - Fix events//enable permissions. - Rename ring-buffer "writer" to "remote". - Rename CONFIG_PROTECTED_NVHE_TESTING to PKVM_SELFTEST to align with Quentin's upcoming selftest - Rebase on 6.13-rc3. Changes since RFC (https://lore.kernel.org/all/20240805173234.3542917-1-vdonnefort@google.com/) - hypervisor trace clock: - mult/shift computed in hyp_trace.c. (John) - Update clock when it deviates from kernel boot clock. (John) - Add trace_clock file. - Separate patch for better readability. - Add a proper reset interface which does not need to teardown the tracing buffers. (Steven) - Return -EPERM on trace access. (Steven) - Add per-cpu trace file. - Automatically teardown and free the tracing buffer when it is empty, without readers and not currently tracing. - Show in buffer_size_kb if the buffer is loaded in the hypervisor or not. - Extend tests to cover reset and unload. - CC timekeeping folks on relevant patches (Marc) Vincent Donnefort (24): ring-buffer: Introduce ring-buffer remotes tracing: Introduce trace remotes tracing: Add reset to trace remotes tracing: Add init callback to trace remotes tracing: Add events to trace remotes tracing: Add events/ root files to trace remotes tracing: Add helpers to create trace remote events ring-buffer: Expose buffer_data_page material tracing: Introduce simple_ring_buffer tracing: Add a trace remote module for testing tracing: selftests: Add trace remote tests tracing: load/unload page callbacks for simple_ring_buffer tracing: Check for undefined symbols in simple_ring_buffer KVM: arm64: Support unaligned fixmap in the nVHE hyp KVM: arm64: Add .hyp.data section KVM: arm64: Add clock support for the pKVM hyp KVM: arm64: Add tracing capability for the pKVM hyp KVM: arm64: Add trace remote for the pKVM hyp KVM: arm64: Sync boot clock with the pKVM hyp KVM: arm64: Add trace reset to the pKVM hyp KVM: arm64: Add event support to the pKVM hyp and trace remote KVM: arm64: Add hyp_enter/hyp_exit events to pKVM hyp KVM: arm64: Add selftest event support to pKVM hyp tracing: selftests: Add pKVM trace remote tests arch/arm64/include/asm/kvm_asm.h | 8 + arch/arm64/include/asm/kvm_define_hypevents.h | 21 + arch/arm64/include/asm/kvm_hyp.h | 1 - arch/arm64/include/asm/kvm_hypevents.h | 41 + arch/arm64/include/asm/kvm_hyptrace.h | 26 + arch/arm64/include/asm/sections.h | 1 + arch/arm64/kernel/image-vars.h | 6 + arch/arm64/kernel/vmlinux.lds.S | 36 +- arch/arm64/kvm/Kconfig | 18 + arch/arm64/kvm/Makefile | 2 + arch/arm64/kvm/arm.c | 11 + arch/arm64/kvm/hyp/include/nvhe/arm-smccc.h | 13 + arch/arm64/kvm/hyp/include/nvhe/clock.h | 16 + .../kvm/hyp/include/nvhe/define_events.h | 21 + arch/arm64/kvm/hyp/include/nvhe/trace.h | 59 ++ arch/arm64/kvm/hyp/nvhe/Makefile | 1 + arch/arm64/kvm/hyp/nvhe/clock.c | 65 ++ arch/arm64/kvm/hyp/nvhe/events.c | 36 + arch/arm64/kvm/hyp/nvhe/ffa.c | 2 +- arch/arm64/kvm/hyp/nvhe/hyp-main.c | 86 ++ arch/arm64/kvm/hyp/nvhe/hyp.lds.S | 8 + arch/arm64/kvm/hyp/nvhe/mm.c | 2 +- arch/arm64/kvm/hyp/nvhe/psci-relay.c | 5 +- arch/arm64/kvm/hyp/nvhe/setup.c | 4 + arch/arm64/kvm/hyp/nvhe/switch.c | 5 +- arch/arm64/kvm/hyp/nvhe/trace.c | 286 ++++++ arch/arm64/kvm/hyp_trace.c | 385 ++++++++ arch/arm64/kvm/hyp_trace.h | 11 + arch/arm64/kvm/pkvm.c | 1 + include/linux/ring_buffer.h | 102 +- include/linux/simple_ring_buffer.h | 57 ++ include/linux/trace_remote.h | 27 + include/linux/trace_remote_event.h | 33 + include/trace/define_remote_events.h | 73 ++ kernel/trace/Kconfig | 14 + kernel/trace/Makefile | 19 + kernel/trace/remote_test.c | 259 +++++ kernel/trace/remote_test_events.h | 10 + kernel/trace/ring_buffer.c | 254 ++++- kernel/trace/simple_ring_buffer.c | 404 ++++++++ kernel/trace/trace.c | 2 +- kernel/trace/trace.h | 6 + kernel/trace/trace_remote.c | 920 ++++++++++++++++++ .../ftrace/test.d/remotes/buffer_size.tc | 24 + .../selftests/ftrace/test.d/remotes/functions | 33 + .../ftrace/test.d/remotes/pkvm/buffer_size.tc | 10 + .../ftrace/test.d/remotes/pkvm/reset.tc | 10 + .../ftrace/test.d/remotes/pkvm/trace_pipe.tc | 10 + .../ftrace/test.d/remotes/pkvm/unloading.tc | 10 + .../selftests/ftrace/test.d/remotes/reset.tc | 105 ++ .../ftrace/test.d/remotes/trace_pipe.tc | 57 ++ .../ftrace/test.d/remotes/unloading.tc | 36 + 52 files changed, 3599 insertions(+), 53 deletions(-) create mode 100644 arch/arm64/include/asm/kvm_define_hypevents.h create mode 100644 arch/arm64/include/asm/kvm_hypevents.h create mode 100644 arch/arm64/include/asm/kvm_hyptrace.h create mode 100644 arch/arm64/kvm/hyp/include/nvhe/arm-smccc.h create mode 100644 arch/arm64/kvm/hyp/include/nvhe/clock.h create mode 100644 arch/arm64/kvm/hyp/include/nvhe/define_events.h create mode 100644 arch/arm64/kvm/hyp/include/nvhe/trace.h create mode 100644 arch/arm64/kvm/hyp/nvhe/clock.c create mode 100644 arch/arm64/kvm/hyp/nvhe/events.c create mode 100644 arch/arm64/kvm/hyp/nvhe/trace.c create mode 100644 arch/arm64/kvm/hyp_trace.c create mode 100644 arch/arm64/kvm/hyp_trace.h create mode 100644 include/linux/simple_ring_buffer.h create mode 100644 include/linux/trace_remote.h create mode 100644 include/linux/trace_remote_event.h create mode 100644 include/trace/define_remote_events.h create mode 100644 kernel/trace/remote_test.c create mode 100644 kernel/trace/remote_test_events.h create mode 100644 kernel/trace/simple_ring_buffer.c create mode 100644 kernel/trace/trace_remote.c create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/buffer_size.tc create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/functions create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/pkvm/buffer_size.tc create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/pkvm/reset.tc create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/pkvm/trace_pipe.tc create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/pkvm/unloading.tc create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/reset.tc create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/trace_pipe.tc create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/unloading.tc base-commit: 02ddfb981de88a2c15621115dd7be2431252c568 -- 2.49.0.967.g6a0df3ecc3-goog