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, 62 insertions, 0 deletions

diff --git a/lib/kunit/string-stream.h b/lib/kunit/string-stream.h
new file mode 100644
index 000000000..7be2450c7
--- /dev/null
+++ b/lib/kunit/string-stream.h
@@ -0,0 +1,62 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * C++ stream style string builder used in KUnit for building messages.
+ *
+ * Copyright (C) 2019, Google LLC.
+ * Author: Brendan Higgins <brendanhiggins@google.com>
+ */
+
+#ifndef _KUNIT_STRING_STREAM_H
+#define _KUNIT_STRING_STREAM_H
+
+#include <linux/spinlock.h>
+#include <linux/types.h>
+#include <linux/stdarg.h>
+
+struct string_stream_fragment {
+	struct list_head node;
+	char *fragment;
+};
+
+struct string_stream {
+	size_t length;
+	struct list_head fragments;
+	/* length and fragments are protected by this lock */
+	spinlock_t lock;
+	gfp_t gfp;
+	bool append_newlines;
+};
+
+struct kunit;
+
+struct string_stream *kunit_alloc_string_stream(struct kunit *test, gfp_t gfp);
+void kunit_free_string_stream(struct kunit *test, struct string_stream *stream);
+
+struct string_stream *alloc_string_stream(gfp_t gfp);
+void free_string_stream(struct string_stream *stream);
+
+int __printf(2, 3) string_stream_add(struct string_stream *stream,
+				     const char *fmt, ...);
+
+int __printf(2, 0) string_stream_vadd(struct string_stream *stream,
+				      const char *fmt,
+				      va_list args);
+
+void string_stream_clear(struct string_stream *stream);
+
+char *string_stream_get_string(struct string_stream *stream);
+
+int string_stream_append(struct string_stream *stream,
+			 struct string_stream *other);
+
+bool string_stream_is_empty(struct string_stream *stream);
+
+void string_stream_destroy(struct string_stream *stream);
+
+static inline void string_stream_set_append_newlines(struct string_stream *stream,
+						     bool append_newlines)
+{
+	stream->append_newlines = append_newlines;
+}
+
+#endif /* _KUNIT_STRING_STREAM_H */