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, 30 insertions, 0 deletions

diff --git a/drivers/md/bcache/Kconfig b/drivers/md/bcache/Kconfig
new file mode 100644
index 000000000..b2d10063d
--- /dev/null
+++ b/drivers/md/bcache/Kconfig
@@ -0,0 +1,30 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+config BCACHE
+	tristate "Block device as cache"
+	select BLOCK_HOLDER_DEPRECATED if SYSFS
+	select CRC64
+	select CLOSURES
+	help
+	Allows a block device to be used as cache for other devices; uses
+	a btree for indexing and the layout is optimized for SSDs.
+
+	See Documentation/admin-guide/bcache.rst for details.
+
+config BCACHE_DEBUG
+	bool "Bcache debugging"
+	depends on BCACHE
+	help
+	Don't select this option unless you're a developer
+
+	Enables extra debugging tools, allows expensive runtime checks to be
+	turned on.
+
+config BCACHE_ASYNC_REGISTRATION
+	bool "Asynchronous device registration"
+	depends on BCACHE
+	help
+	Add a sysfs file /sys/fs/bcache/register_async. Writing registering
+	device path into this file will returns immediately and the real
+	registration work is handled in kernel work queue in asynchronous
+	way.