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, 168 insertions, 0 deletions

diff --git a/drivers/scsi/arm/msgqueue.c b/drivers/scsi/arm/msgqueue.c
new file mode 100644
index 000000000..581158313
--- /dev/null
+++ b/drivers/scsi/arm/msgqueue.c
@@ -0,0 +1,168 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  linux/drivers/acorn/scsi/msgqueue.c
+ *
+ *  Copyright (C) 1997-1998 Russell King
+ *
+ *  message queue handling
+ */
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/stddef.h>
+#include <linux/init.h>
+
+#include "msgqueue.h"
+
+/*
+ * Function: struct msgqueue_entry *mqe_alloc(MsgQueue_t *msgq)
+ * Purpose : Allocate a message queue entry
+ * Params  : msgq - message queue to claim entry for
+ * Returns : message queue entry or NULL.
+ */
+static struct msgqueue_entry *mqe_alloc(MsgQueue_t *msgq)
+{
+	struct msgqueue_entry *mq;
+
+	if ((mq = msgq->free) != NULL)
+		msgq->free = mq->next;
+
+	return mq;
+}
+
+/*
+ * Function: void mqe_free(MsgQueue_t *msgq, struct msgqueue_entry *mq)
+ * Purpose : free a message queue entry
+ * Params  : msgq - message queue to free entry from
+ *	     mq   - message queue entry to free
+ */
+static void mqe_free(MsgQueue_t *msgq, struct msgqueue_entry *mq)
+{
+	if (mq) {
+		mq->next = msgq->free;
+		msgq->free = mq;
+	}
+}
+
+/*
+ * Function: void msgqueue_initialise(MsgQueue_t *msgq)
+ * Purpose : initialise a message queue
+ * Params  : msgq - queue to initialise
+ */
+void msgqueue_initialise(MsgQueue_t *msgq)
+{
+	int i;
+
+	msgq->qe = NULL;
+	msgq->free = &msgq->entries[0];
+
+	for (i = 0; i < NR_MESSAGES; i++)
+		msgq->entries[i].next = &msgq->entries[i + 1];
+
+	msgq->entries[NR_MESSAGES - 1].next = NULL;
+}
+
+
+/*
+ * Function: void msgqueue_free(MsgQueue_t *msgq)
+ * Purpose : free a queue
+ * Params  : msgq - queue to free
+ */
+void msgqueue_free(MsgQueue_t *msgq)
+{
+}
+
+/*
+ * Function: int msgqueue_msglength(MsgQueue_t *msgq)
+ * Purpose : calculate the total length of all messages on the message queue
+ * Params  : msgq - queue to examine
+ * Returns : number of bytes of messages in queue
+ */
+int msgqueue_msglength(MsgQueue_t *msgq)
+{
+	struct msgqueue_entry *mq = msgq->qe;
+	int length = 0;
+
+	for (mq = msgq->qe; mq; mq = mq->next)
+		length += mq->msg.length;
+
+	return length;
+}
+
+/*
+ * Function: struct message *msgqueue_getmsg(MsgQueue_t *msgq, int msgno)
+ * Purpose : return a message
+ * Params  : msgq   - queue to obtain message from
+ *	   : msgno  - message number
+ * Returns : pointer to message string, or NULL
+ */
+struct message *msgqueue_getmsg(MsgQueue_t *msgq, int msgno)
+{
+	struct msgqueue_entry *mq;
+
+	for (mq = msgq->qe; mq && msgno; mq = mq->next, msgno--);
+
+	return mq ? &mq->msg : NULL;
+}
+
+/*
+ * Function: int msgqueue_addmsg(MsgQueue_t *msgq, int length, ...)
+ * Purpose : add a message onto a message queue
+ * Params  : msgq   - queue to add message on
+ *	     length - length of message
+ *	     ...    - message bytes
+ * Returns : != 0 if successful
+ */
+int msgqueue_addmsg(MsgQueue_t *msgq, int length, ...)
+{
+	struct msgqueue_entry *mq = mqe_alloc(msgq);
+	va_list ap;
+
+	if (mq) {
+		struct msgqueue_entry **mqp;
+		int i;
+
+		va_start(ap, length);
+		for (i = 0; i < length; i++)
+			mq->msg.msg[i] = va_arg(ap, unsigned int);
+		va_end(ap);
+
+		mq->msg.length = length;
+		mq->msg.fifo = 0;
+		mq->next = NULL;
+
+		mqp = &msgq->qe;
+		while (*mqp)
+			mqp = &(*mqp)->next;
+
+		*mqp = mq;
+	}
+
+	return mq != NULL;
+}
+
+/*
+ * Function: void msgqueue_flush(MsgQueue_t *msgq)
+ * Purpose : flush all messages from message queue
+ * Params  : msgq - queue to flush
+ */
+void msgqueue_flush(MsgQueue_t *msgq)
+{
+	struct msgqueue_entry *mq, *mqnext;
+
+	for (mq = msgq->qe; mq; mq = mqnext) {
+		mqnext = mq->next;
+		mqe_free(msgq, mq);
+	}
+	msgq->qe = NULL;
+}
+
+EXPORT_SYMBOL(msgqueue_initialise);
+EXPORT_SYMBOL(msgqueue_free);
+EXPORT_SYMBOL(msgqueue_msglength);
+EXPORT_SYMBOL(msgqueue_getmsg);
+EXPORT_SYMBOL(msgqueue_addmsg);
+EXPORT_SYMBOL(msgqueue_flush);
+
+MODULE_AUTHOR("Russell King");
+MODULE_DESCRIPTION("SCSI message queue handling");
+MODULE_LICENSE("GPL");