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, 33 insertions, 0 deletions

diff --git a/include/kunit/visibility.h b/include/kunit/visibility.h
new file mode 100644
index 000000000..7c34c8ffc
--- /dev/null
+++ b/include/kunit/visibility.h
@@ -0,0 +1,33 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * KUnit API to allow symbols to be conditionally visible during KUnit
+ * testing
+ *
+ * Copyright (C) 2022, Google LLC.
+ * Author: Rae Moar <rmoar@google.com>
+ */
+
+#ifndef _KUNIT_VISIBILITY_H
+#define _KUNIT_VISIBILITY_H
+
+#if IS_ENABLED(CONFIG_KUNIT)
+    /**
+     * VISIBLE_IF_KUNIT - A macro that sets symbols to be static if
+     * CONFIG_KUNIT is not enabled. Otherwise if CONFIG_KUNIT is enabled
+     * there is no change to the symbol definition.
+     */
+    #define VISIBLE_IF_KUNIT
+    /**
+     * EXPORT_SYMBOL_IF_KUNIT(symbol) - Exports symbol into
+     * EXPORTED_FOR_KUNIT_TESTING namespace only if CONFIG_KUNIT is
+     * enabled. Must use MODULE_IMPORT_NS("EXPORTED_FOR_KUNIT_TESTING")
+     * in test file in order to use symbols.
+     * @symbol: the symbol identifier to export
+     */
+    #define EXPORT_SYMBOL_IF_KUNIT(symbol) EXPORT_SYMBOL_NS(symbol, "EXPORTED_FOR_KUNIT_TESTING")
+#else
+    #define VISIBLE_IF_KUNIT static
+    #define EXPORT_SYMBOL_IF_KUNIT(symbol)
+#endif
+
+#endif /* _KUNIT_VISIBILITY_H */