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

Pull ring-buffer updates from Steven Rostedt:

- Add remote buffers for pKVM

pKVM has a hype

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

Pull 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
...

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tracing: Add a trace remote module for testing

Add a module to help testing the tracefs support for trace remotes. This
module:

* Use simple_ring_buffer to write into a ring-buffer.
* Declare a

tracing: Add a trace remote module for testing

Add a module to help testing the tracefs support for trace remotes. This
module:

* Use simple_ring_buffer to write into a ring-buffer.
* Declare a single "selftest" event that can be triggered from
user-space.
* Register a "test" trace remote.

This is intended to be used by trace remote selftests.

Link: https://patch.msgid.link/20260309162516.2623589-15-vdonnefort@google.com
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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