KVM: SEV: Do cache maintenance on the source VM during intra-host migrationgrafted

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 <fane@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260923163721.1584779-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 46 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/ppc-memtrace b/Documentation/ABI/testing/ppc-memtrace
new file mode 100644
index 000000000..9606aed33
--- /dev/null
+++ b/Documentation/ABI/testing/ppc-memtrace
@@ -0,0 +1,46 @@
+What:		/sys/kernel/debug/powerpc/memtrace
+Date:		Aug 2017
+KernelVersion:	4.14
+Contact:	linuxppc-dev@lists.ozlabs.org
+Description:	This folder contains the relevant debugfs files for the
+		hardware trace macro to use. CONFIG_PPC64_HARDWARE_TRACING
+		must be set.
+
+What:		/sys/kernel/debug/powerpc/memtrace/enable
+Date:		Aug 2017
+KernelVersion:	4.14
+Contact:	linuxppc-dev@lists.ozlabs.org
+Description:	Write an integer containing the size in bytes of the memory
+		you want removed from each NUMA node to this file - it must be
+		aligned to the memblock size. This amount of RAM will be removed
+		from each NUMA node in the kernel mappings and the following
+		debugfs files will be created. Once memory is successfully
+		removed from each node, the following files are created. To
+		re-add memory to the kernel, echo 0 into this file (it will be
+		automatically onlined).
+
+What:		/sys/kernel/debug/powerpc/memtrace/<node-id>
+Date:		Aug 2017
+KernelVersion:	4.14
+Contact:	linuxppc-dev@lists.ozlabs.org
+Description:	This directory contains information about the removed memory
+		from the specific NUMA node.
+
+What:		/sys/kernel/debug/powerpc/memtrace/<node-id>/size
+Date:		Aug 2017
+KernelVersion:	4.14
+Contact:	linuxppc-dev@lists.ozlabs.org
+Description:	This contains the size of the memory removed from the node.
+
+What:		/sys/kernel/debug/powerpc/memtrace/<node-id>/start
+Date:		Aug 2017
+KernelVersion:	4.14
+Contact:	linuxppc-dev@lists.ozlabs.org
+Description:	This contains the start address of the removed memory.
+
+What:		/sys/kernel/debug/powerpc/memtrace/<node-id>/trace
+Date:		Aug 2017
+KernelVersion:	4.14
+Contact:	linuxppc-dev@lists.ozlabs.org
+Description:	This is where the hardware trace macro will output the trace
+		it generates.