KVM: Don't pre-reserve xarray entries when storing empty/NULL attributesgrafted

Skip the xarray reservation loop when clearing all memory attributes, as
storing NULL only erases the entry and never needs to allocate, so no
reservation (and no cleanup of a failed one) is required in that case.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: David Ballesteros <davimaba.v@proton.me>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com
[sean: split to separate patch]
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 79 insertions, 0 deletions

diff --git a/drivers/scsi/arm/msgqueue.h b/drivers/scsi/arm/msgqueue.h
new file mode 100644
index 000000000..4bcc400f5
--- /dev/null
+++ b/drivers/scsi/arm/msgqueue.h
@@ -0,0 +1,79 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ *  linux/drivers/acorn/scsi/msgqueue.h
+ *
+ *  Copyright (C) 1997 Russell King
+ *
+ *  message queue handling
+ */
+#ifndef MSGQUEUE_H
+#define MSGQUEUE_H
+
+struct message {
+    char msg[8];
+    int length;
+    int fifo;
+};
+
+struct msgqueue_entry {
+    struct message msg;
+    struct msgqueue_entry *next;
+};
+
+#define NR_MESSAGES 4
+
+typedef struct {
+    struct msgqueue_entry *qe;
+    struct msgqueue_entry *free;
+    struct msgqueue_entry entries[NR_MESSAGES];
+} MsgQueue_t;
+
+/*
+ * Function: void msgqueue_initialise(MsgQueue_t *msgq)
+ * Purpose : initialise a message queue
+ * Params  : msgq - queue to initialise
+ */
+extern void msgqueue_initialise(MsgQueue_t *msgq);
+
+/*
+ * Function: void msgqueue_free(MsgQueue_t *msgq)
+ * Purpose : free a queue
+ * Params  : msgq - queue to free
+ */
+extern 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
+ */
+extern int msgqueue_msglength(MsgQueue_t *msgq);
+
+/*
+ * Function: struct message *msgqueue_getmsg(MsgQueue_t *msgq, int msgno)
+ * Purpose : return a message & its length
+ * Params  : msgq   - queue to obtain message from
+ *         : msgno  - message number
+ * Returns : pointer to message string, or NULL
+ */
+extern struct message *msgqueue_getmsg(MsgQueue_t *msgq, int msgno);
+
+/*
+ * 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
+ */
+extern int msgqueue_addmsg(MsgQueue_t *msgq, int length, ...);
+
+/*
+ * Function: void msgqueue_flush(MsgQueue_t *msgq)
+ * Purpose : flush all messages from message queue
+ * Params  : msgq - queue to flush
+ */
+extern void msgqueue_flush(MsgQueue_t *msgq);
+
+#endif