From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f74.google.com (mail-wr1-f74.google.com [209.85.221.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 929592DF128 for ; Thu, 19 Feb 2026 15:03:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.74 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771513401; cv=none; b=meHALp4mXuXegOi9ulqe9vtpCPodoxAetfpf7+AYur4jslxX9KU7KIwzM5p84IzMdMxSILK3n5AfWrmH+ARzqwI7LF1CP4Lc008Xui2Edi9JpNnguxj2sMCBlN052P0ddIaib62Vi92d1pimTNI/I0DysWPuh7Q6Xrjuo9I5tGA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771513401; c=relaxed/simple; bh=uBfJTJGlZyJPRUmkwG6uhEhK2r2iRxXRKjWb09s0vnQ=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=IcyEgG5fhfXzOBXuRxCQRA0cjrHlaZ8tgCpVX7gx3S+Wb1OrqEd+Q274elgRCCpnU0u4d8L3ccIp8ApLdSC7oZP463EWZR12/vLqf1sJFs71Vw+YrhqqhH6mLmHRbAwGeyPuoLKPLL9rFPIb8k3YabGb4oxOpMgKKeWdd5b4W40= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--vdonnefort.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=WIgAeHMh; arc=none smtp.client-ip=209.85.221.74 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--vdonnefort.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="WIgAeHMh" Received: by mail-wr1-f74.google.com with SMTP id ffacd0b85a97d-43624564fc9so988914f8f.2 for ; Thu, 19 Feb 2026 07:03:19 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1771513398; x=1772118198; darn=vger.kernel.org; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=+sMZ7805PZwY51si6N+AufTW0sgIBbsPqYNSbMWUSu4=; b=WIgAeHMhrB+OnDPPfNL8X0cFtg9pTKL8/H+cLzWGUDRc+G3NjcjoA3NuAe0C9/+z94 mvX9IjNsd9AOKM9MPL6zmAXlEyAJ90YdkQXH4UrTeyDIZmAT86r8D6QDwrTjtH5HF/EI bmtFv6CpDtl7dcG0C2+9XK15QoykVrsPY9zmbHPDoW8fR5m2LlD2gMCwRk5iRAfSz+rz O6npHX+1g7AhrO5zhJX5sbHq+s87ouhMSLHELH1KENK9JO/3B+OBkA8BvA2o916Ln6+t yHLMto/nSxKu99+LODKh3MoX3uhr5GpEkVxG6bCWRY6c6ibIFTQgTEKyAGMPjQqWcKlB s+Fg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1771513398; x=1772118198; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=+sMZ7805PZwY51si6N+AufTW0sgIBbsPqYNSbMWUSu4=; b=KEsXEQ4a3241EPdWpqMTkouIDDz3puOcQ8egqQ/mqY2buA3i5R38qvFF5V4CJIdV+3 9/rScvyGL7vqI06glRVJPgjK0HgTG5PTNQTb0QCQu0jPIBN5upn25HKrxtcLH3VlqWqk wLggSqvVtBnbp8ZlYl4JXYl1ZMiCrcJYSLEgEkNsDCanlpfHlfigZyXoOKvfMnAN0TAw pEfNBln+eVxsLEFln1hHQXheiN5U1DaR4VO8aRWUaYAQymdzSy30J9rag1rhos+zVj6i 1XTJjD2a/UHXMlstWERD4hwzQxY5acHXHpUBIcb6HzhwlztpzezY/2ym2v7wWvupb4Q5 D5wQ== X-Forwarded-Encrypted: i=1; AJvYcCXhQAim736VKB+sJpGt6C+IkjTqKJhcSmwbgoUmorDc2yh3bOWWEgV50LQXkiqYo78nUu/hfPMd04Ch6CR4jUgSXfc=@vger.kernel.org X-Gm-Message-State: AOJu0YwpUYhnH5tPQAyPrbF2ROCc48ImzmNg5hzimu3XwLCkm/xOdips Gq54BfikiUMSUrpUb+f7DaKfN8dK8ZfDszcIWWCDoQM7+WPbIJpMQk02CWCiRVj9O1KLecRLcTq /nTOuSwcOmqV7sQZ4x1VVew== X-Received: from wmol21.prod.google.com ([2002:a05:600c:47d5:b0:480:680f:94dd]) (user=vdonnefort job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:37cc:b0:477:58af:a91d with SMTP id 5b1f17b1804b1-48379b93370mr304716025e9.5.1771513397673; Thu, 19 Feb 2026 07:03:17 -0800 (PST) Date: Thu, 19 Feb 2026 15:02:37 +0000 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.53.0.335.g19a08e0c02-goog Message-ID: <20260219150307.14538-1-vdonnefort@google.com> Subject: [PATCH v12 00/30] Tracefs support for pKVM From: Vincent Donnefort To: rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, linux-trace-kernel@vger.kernel.org, maz@kernel.org, oliver.upton@linux.dev, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com Cc: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, jstultz@google.com, qperret@google.com, will@kernel.org, aneesh.kumar@kernel.org, kernel-team@android.com, linux-kernel@vger.kernel.org, Vincent Donnefort Content-Type: text/plain; charset="UTF-8" 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. 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 |-- events | |-- enable | |-- header_event | |-- header_page | `-- test | `-- selftest | |-- enable | |-- format | `-- id |-- per_cpu | `-- cpu0 | |-- trace | `-- trace_pipe |-- trace |-- trace_pipe |-- tracing_on 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 v11 (https://lore.kernel.org/all/20260131132848.254084-1-vdonnefort@google.com/) - Fix kerneldoc (Steven) - Remove useless ring_buffer_event_data type cast (Steven) - Fix __free_ring_buffer_iter() (Steven) - Move trace seq locking into start/stop (Steven) changes since v10 (https://lore.kernel.org/all/20260126104419.1649811-1-vdonnefort@google.com/) - Move kerneldoc to .c files (Steven) - Return EBUSY on buffer_size_kb write if buffer is loaded (Steven) - Remove rb_iter/rb_iters union in trace_remote_iterator (Steven) - Rename a refactor trace file seq_operations (Steven) - Make trace_get_cpu() accessible to trace_remote.c (Steven) - Remove unnecessary cpus_read_unlock() (Steven) - !preempt on remote_test driver buffer writing (Steven) - Do not fail selftest if cpu/online is unavailable (Steven) - Add rational for trace_remote into documentation (Steven) changes since v9 (https://lore.kernel.org/all/20251202093623.2337860-1-vdonnefort@google.com/) - Add vCPU PID to hyp_enter/hyp_exit (Marc) - Remove useless X1 setting for tracing HVCs (Marc) - Fix REMOTE_PRINTK_COUNT_ARGS() - Rebase on 6.19-rc7 Changes since v8 (https://lore.kernel.org/all/20251107093840.3779150-1-vdonnefort@google.com/) - Do not enable tracing if unstable cnvct (Marc) - Add support for nVHE (Marc) - Add PKVM_DISABLE_STAGE2_ON_PANIC (Marc) - NVHE_EL2_TRACING depends on NVHE_EL2_DEBUG (Marc) - Add a reason for hyp_enter/hyp_exit events (Marc) - Remove PKVM_SELFTESTS in favour of NVHE_EL2_DEBUG - Add wrapper for arm_smccc_1_2, now used in nvhe/ffa.c Changes since v7 (https://lore.kernel.org/all/20251003133825.2068970-1-vdonnefort@google.com/) - Add missing EXPORT_SYMBOL_GPL for remote_test.ko - Rebase on 6.18-rc4 Changes since v6 (https://lore.kernel.org/all/20250821081412.1008261-1-vdonnefort@google.com/) - Add requires field to the selftest (Masami) - Use guard() for ring_buffer_poll_remote (Steven) - Rename ring_buffer_remote() to ring_buffer_alloc_remote() (Steven) - kerneldoc for trace_buffer_remote and simple_ring_buffer (Steven) - Validate trace_buffer_desc size in trace_remote_alloc_buffer (Steven) - Add non-consuming ring-buffer read (Steven) - Add spinning failsafe in simple_ring_buffer (Steven) - Range check for hyp_trace_desc::bpages_backing_* in hyp_trace_desc_validate() - unsigned int cpu in hyp_trace_desc_validate() - Fix event/format file - Add tests with an offline CPU - Add tests for non-consuming read - Add documentation - Rebase on 6.17 Changes since v5 (https://lore.kernel.org/all/20250516134031.661124-1-vdonnefort@google.com/) - Add tishift lib to the hyp (Aneesh) - Rebase on 6.17-rc2 Changes since v4 (https://lore.kernel.org/all/20250506164820.515876-1-vdonnefort@google.com/) - Extend meta-page with pages_touched and pages_lost - Create ring_buffer_types.h - Fix simple_ring_buffer build for 32-bits arch and x86 - Try unload buffer on reset (+ test) - Minor renaming and comments 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 (30): ring-buffer: Add page statistics to the meta-page ring-buffer: Store bpage pointers into subbuf_ids ring-buffer: Introduce ring-buffer remotes ring-buffer: Add non-consuming read for ring-buffer remotes tracing: Introduce trace remotes tracing: Add reset to trace remotes tracing: Add non-consuming read 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: Export buffer_data_page and macros tracing: Introduce simple_ring_buffer tracing: Add a trace remote module for testing tracing: selftests: Add trace remote tests Documentation: tracing: Add tracing remotes tracing: load/unload page callbacks for simple_ring_buffer tracing: Check for undefined symbols in simple_ring_buffer KVM: arm64: Add PKVM_DISABLE_STAGE2_ON_PANIC KVM: arm64: Add clock support to nVHE/pKVM hyp KVM: arm64: Initialise hyp_nr_cpus for nVHE hyp KVM: arm64: Support unaligned fixmap in the pKVM hyp KVM: arm64: Add tracing capability for the nVHE/pKVM hyp KVM: arm64: Add trace remote for the nVHE/pKVM hyp KVM: arm64: Sync boot clock with the nVHE/pKVM hyp KVM: arm64: Add trace reset to the nVHE/pKVM hyp KVM: arm64: Add event support to the nVHE/pKVM hyp and trace remote KVM: arm64: Add hyp_enter/hyp_exit events to nVHE/pKVM hyp KVM: arm64: Add selftest event support to nVHE/pKVM hyp tracing: selftests: Add hypervisor trace remote tests Documentation/trace/index.rst | 11 + Documentation/trace/remotes.rst | 66 + arch/arm64/include/asm/kvm_asm.h | 8 + arch/arm64/include/asm/kvm_define_hypevents.h | 16 + arch/arm64/include/asm/kvm_host.h | 3 + arch/arm64/include/asm/kvm_hyp.h | 4 +- arch/arm64/include/asm/kvm_hypevents.h | 60 + arch/arm64/include/asm/kvm_hyptrace.h | 26 + arch/arm64/kernel/image-vars.h | 4 + arch/arm64/kernel/vmlinux.lds.S | 18 + arch/arm64/kvm/Kconfig | 64 +- arch/arm64/kvm/Makefile | 2 + arch/arm64/kvm/arm.c | 12 +- arch/arm64/kvm/handle_exit.c | 2 +- arch/arm64/kvm/hyp/include/nvhe/arm-smccc.h | 23 + arch/arm64/kvm/hyp/include/nvhe/clock.h | 16 + .../kvm/hyp/include/nvhe/define_events.h | 14 + arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 2 - arch/arm64/kvm/hyp/include/nvhe/trace.h | 70 + arch/arm64/kvm/hyp/nvhe/Makefile | 6 +- arch/arm64/kvm/hyp/nvhe/clock.c | 65 + arch/arm64/kvm/hyp/nvhe/events.c | 25 + arch/arm64/kvm/hyp/nvhe/ffa.c | 28 +- arch/arm64/kvm/hyp/nvhe/host.S | 2 +- arch/arm64/kvm/hyp/nvhe/hyp-main.c | 87 +- arch/arm64/kvm/hyp/nvhe/hyp.lds.S | 6 + arch/arm64/kvm/hyp/nvhe/mm.c | 4 +- arch/arm64/kvm/hyp/nvhe/psci-relay.c | 7 +- arch/arm64/kvm/hyp/nvhe/setup.c | 4 +- arch/arm64/kvm/hyp/nvhe/stacktrace.c | 6 +- arch/arm64/kvm/hyp/nvhe/switch.c | 5 +- arch/arm64/kvm/hyp/nvhe/trace.c | 306 ++++ arch/arm64/kvm/hyp_trace.c | 443 ++++++ arch/arm64/kvm/hyp_trace.h | 11 + arch/arm64/kvm/stacktrace.c | 8 +- fs/tracefs/inode.c | 1 + include/linux/ring_buffer.h | 58 + include/linux/ring_buffer_types.h | 41 + include/linux/simple_ring_buffer.h | 65 + include/linux/trace_remote.h | 48 + include/linux/trace_remote_event.h | 33 + include/trace/define_remote_events.h | 73 + include/uapi/linux/trace_mmap.h | 8 +- kernel/trace/Kconfig | 14 + kernel/trace/Makefile | 20 + kernel/trace/remote_test.c | 261 ++++ kernel/trace/remote_test_events.h | 10 + kernel/trace/ring_buffer.c | 356 ++++- kernel/trace/simple_ring_buffer.c | 517 +++++++ kernel/trace/trace.c | 4 +- kernel/trace/trace.h | 7 + kernel/trace/trace_remote.c | 1368 +++++++++++++++++ .../ftrace/test.d/remotes/buffer_size.tc | 25 + .../selftests/ftrace/test.d/remotes/functions | 88 ++ .../test.d/remotes/hypervisor/buffer_size.tc | 11 + .../ftrace/test.d/remotes/hypervisor/reset.tc | 11 + .../ftrace/test.d/remotes/hypervisor/trace.tc | 11 + .../test.d/remotes/hypervisor/trace_pipe.tc | 11 + .../test.d/remotes/hypervisor/unloading.tc | 11 + .../selftests/ftrace/test.d/remotes/reset.tc | 90 ++ .../selftests/ftrace/test.d/remotes/trace.tc | 127 ++ .../ftrace/test.d/remotes/trace_pipe.tc | 127 ++ .../ftrace/test.d/remotes/unloading.tc | 41 + 63 files changed, 4751 insertions(+), 120 deletions(-) create mode 100644 Documentation/trace/remotes.rst 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/ring_buffer_types.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/hypervisor/buffer_size.tc create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/hypervisor/reset.tc create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/hypervisor/trace.tc create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/hypervisor/trace_pipe.tc create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/hypervisor/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.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: 2b7a25df823dc7d8f56f8ce7c2d2dac391cea9c2 -- 2.53.0.335.g19a08e0c02-goog