From 93de2a6a4b91b72607136dd656edf03fb399d27f Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 23 Sep 2026 09:37:21 -0700 Subject: KVM: SEV: Do cache maintenance on the source VM during intra-host migration Manually perform cache maintenance on the source VM during intra-host migration to ensure no stale data is left in CPU caches after the VM is destroyed. Because the source VM is "converted" to a non-SEV VM, KVM's memory reclaim flows won't trigger cache maintenance, e.g. when all guest memory is reclaimed in response to detaching from the mmu_notifier. Note, relying on the destination VM to do cache maintenance isn't an option as KVM doesn't require identical guest memory configurations, i.e. the source VM may have access to memory that the destination VM does not. Enforcing equivalent memory configurations is infeasible, as it would require a *deep* comparison of memslots, e.g. to verify that not only are the memslot identical, but what the memslots point at is also identical. Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration") Cc: stable@vger.kernel.org Reported-by: Stefan Teodorescu Signed-off-by: Sean Christopherson Message-ID: <20260923163721.1584779-3-seanjc@google.com> Signed-off-by: Paolo Bonzini --- Documentation/trace/remotes.rst | 66 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 66 insertions(+) create mode 100644 Documentation/trace/remotes.rst (limited to 'Documentation/trace/remotes.rst') diff --git a/Documentation/trace/remotes.rst b/Documentation/trace/remotes.rst new file mode 100644 index 000000000..1f9d764f6 --- /dev/null +++ b/Documentation/trace/remotes.rst @@ -0,0 +1,66 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=============== +Tracing Remotes +=============== + +:Author: Vincent Donnefort + +Overview +======== +Firmware and hypervisors are black boxes to the kernel. Having a way to see what +they are doing can be useful to debug both. This is where remote tracing buffers +come in. A remote tracing buffer is a ring buffer executed by the firmware or +hypervisor into memory that is memory mapped to the host kernel. This is similar +to how user space memory maps the kernel ring buffer but in this case the kernel +is acting like user space and the firmware or hypervisor is the "kernel" side. +With a trace remote ring buffer, the firmware and hypervisor can record events +for which the host kernel can see and expose to user space. + +Register a remote +================= +A remote must provide a set of callbacks `struct trace_remote_callbacks` whom +description can be found below. Those callbacks allows Tracefs to enable and +disable tracing and events, to load and unload a tracing buffer (a set of +ring-buffers) and to swap a reader page with the head page, which enables +consuming reading. + +.. kernel-doc:: include/linux/trace_remote.h + +Once registered, an instance will appear for this remote in the Tracefs +directory **remotes/**. Buffers can then be read using the usual Tracefs files +**trace_pipe** and **trace**. + +Declare a remote event +====================== +Macros are provided to ease the declaration of remote events, in a similar +fashion to in-kernel events. A declaration must provide an ID, a description of +the event arguments and how to print the event: + +.. code-block:: c + + REMOTE_EVENT(foo, EVENT_FOO_ID, + RE_STRUCT( + re_field(u64, bar) + ), + RE_PRINTK("bar=%lld", __entry->bar) + ); + +Then those events must be declared in a C file with the following: + +.. code-block:: c + + #define REMOTE_EVENT_INCLUDE_FILE foo_events.h + #include + +This will provide a `struct remote_event remote_event_foo` that can be given to +`trace_remote_register`. + +Registered events appear in the remote directory under **events/**. + +Simple ring-buffer +================== +A simple implementation for a ring-buffer writer can be found in +kernel/trace/simple_ring_buffer.c. + +.. kernel-doc:: include/linux/simple_ring_buffer.h -- cgit v1.3.1