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, 61 insertions, 0 deletions

diff --git a/drivers/thunderbolt/configfs.c b/drivers/thunderbolt/configfs.c
new file mode 100644
index 000000000..dc6bc363d
--- /dev/null
+++ b/drivers/thunderbolt/configfs.c
@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * ConfigFS support
+ *
+ * Copyright (C) 2026, Intel Corporation
+ * Author: Mika Westerberg <mika.westerberg@linux.intel.com>
+ */
+
+#include <linux/configfs.h>
+#include <linux/export.h>
+
+#include "tb.h"
+
+static const struct config_item_type tb_root_group_type = {
+	.ct_owner = THIS_MODULE,
+};
+
+static struct configfs_subsystem tb_configfs = {
+	.su_group = {
+		.cg_item = {
+			.ci_namebuf = "thunderbolt",
+			.ci_type = &tb_root_group_type,
+		},
+	},
+};
+
+/**
+ * tb_configfs_register_group() - Register Thunderbolt ConfigFS group
+ * @group: Group to register.
+ *
+ * Registers the new @group under Thunderbolt subsystem ConfigFS.
+ *
+ * Return: 0% in case of success, negative errno otherwise.
+ */
+int tb_configfs_register_group(struct config_group *group)
+{
+	return configfs_register_group(&tb_configfs.su_group, group);
+}
+EXPORT_SYMBOL_GPL(tb_configfs_register_group);
+
+/**
+ * tb_configfs_unregister_group() - Unregister previously registered group
+ * @group: Group to unregister.
+ */
+void tb_configfs_unregister_group(struct config_group *group)
+{
+	configfs_unregister_group(group);
+}
+EXPORT_SYMBOL_GPL(tb_configfs_unregister_group);
+
+int tb_configfs_init(void)
+{
+	config_group_init(&tb_configfs.su_group);
+	mutex_init(&tb_configfs.su_mutex);
+	return configfs_register_subsystem(&tb_configfs);
+}
+
+void tb_configfs_exit(void)
+{
+	configfs_unregister_subsystem(&tb_configfs);
+}