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, 48 insertions, 0 deletions

diff --git a/drivers/soc/apple/mailbox.h b/drivers/soc/apple/mailbox.h
new file mode 100644
index 000000000..f73a8913d
--- /dev/null
+++ b/drivers/soc/apple/mailbox.h
@@ -0,0 +1,48 @@
+/* SPDX-License-Identifier: GPL-2.0-only OR MIT */
+/*
+ * Apple mailbox message format
+ *
+ * Copyright The Asahi Linux Contributors
+ */
+
+#ifndef _APPLE_MAILBOX_H_
+#define _APPLE_MAILBOX_H_
+
+#include <linux/device.h>
+#include <linux/types.h>
+
+/* encodes a single 96bit message sent over the single channel */
+struct apple_mbox_msg {
+	u64 msg0;
+	u32 msg1;
+};
+
+struct apple_mbox {
+	struct device *dev;
+	void __iomem *regs;
+	const struct apple_mbox_hw *hw;
+	bool active;
+
+	int irq_recv_not_empty;
+	int irq_send_empty;
+
+	spinlock_t rx_lock;
+	spinlock_t tx_lock;
+
+	struct completion tx_empty;
+
+	/** Receive callback for incoming messages */
+	void (*rx)(struct apple_mbox *mbox, struct apple_mbox_msg msg, void *cookie);
+	void *cookie;
+};
+
+struct apple_mbox *apple_mbox_get(struct device *dev, int index);
+struct apple_mbox *apple_mbox_get_byname(struct device *dev, const char *name);
+
+int apple_mbox_start(struct apple_mbox *mbox);
+void apple_mbox_stop(struct apple_mbox *mbox);
+int apple_mbox_poll(struct apple_mbox *mbox);
+int apple_mbox_send(struct apple_mbox *mbox, struct apple_mbox_msg msg,
+		    bool atomic);
+
+#endif