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, 45 insertions, 0 deletions

diff --git a/drivers/md/dm-vdo/permassert.h b/drivers/md/dm-vdo/permassert.h
new file mode 100644
index 000000000..c34f2ba65
--- /dev/null
+++ b/drivers/md/dm-vdo/permassert.h
@@ -0,0 +1,45 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2023 Red Hat
+ */
+
+#ifndef PERMASSERT_H
+#define PERMASSERT_H
+
+#include <linux/compiler.h>
+
+#include "errors.h"
+
+/* Utilities for asserting that certain conditions are met */
+
+#define STRINGIFY(X) #X
+
+/*
+ * A hack to apply the "warn if unused" attribute to an integral expression.
+ *
+ * Since GCC doesn't propagate the warn_unused_result attribute to conditional expressions
+ * incorporating calls to functions with that attribute, this function can be used to wrap such an
+ * expression. With optimization enabled, this function contributes no additional instructions, but
+ * the warn_unused_result attribute still applies to the code calling it.
+ */
+static inline int __must_check vdo_must_use(int value)
+{
+	return value;
+}
+
+/* Assert that an expression is true and return an error if it is not. */
+#define VDO_ASSERT(expr, ...) vdo_must_use(__VDO_ASSERT(expr, __VA_ARGS__))
+
+/* Log a message if the expression is not true. */
+#define VDO_ASSERT_LOG_ONLY(expr, ...) __VDO_ASSERT(expr, __VA_ARGS__)
+
+#define __VDO_ASSERT(expr, ...)				      \
+	(likely(expr) ? VDO_SUCCESS			      \
+		      : vdo_assertion_failed(STRINGIFY(expr), __FILE__, __LINE__, __VA_ARGS__))
+
+/* Log an assertion failure message. */
+int vdo_assertion_failed(const char *expression_string, const char *file_name,
+			 int line_number, const char *format, ...)
+	__printf(4, 5);
+
+#endif /* PERMASSERT_H */