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, 63 insertions, 0 deletions

diff --git a/fs/proc/kmsg.c b/fs/proc/kmsg.c
new file mode 100644
index 000000000..2fc92a13f
--- /dev/null
+++ b/fs/proc/kmsg.c
@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/fs/proc/kmsg.c
+ *
+ *  Copyright (C) 1992  by Linus Torvalds
+ *
+ */
+
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/time.h>
+#include <linux/kernel.h>
+#include <linux/poll.h>
+#include <linux/proc_fs.h>
+#include <linux/fs.h>
+#include <linux/syslog.h>
+
+#include <asm/io.h>
+
+static int kmsg_open(struct inode * inode, struct file * file)
+{
+	return do_syslog(SYSLOG_ACTION_OPEN, NULL, 0, SYSLOG_FROM_PROC);
+}
+
+static int kmsg_release(struct inode * inode, struct file * file)
+{
+	(void) do_syslog(SYSLOG_ACTION_CLOSE, NULL, 0, SYSLOG_FROM_PROC);
+	return 0;
+}
+
+static ssize_t kmsg_read(struct file *file, char __user *buf,
+			 size_t count, loff_t *ppos)
+{
+	if ((file->f_flags & O_NONBLOCK) &&
+	    !do_syslog(SYSLOG_ACTION_SIZE_UNREAD, NULL, 0, SYSLOG_FROM_PROC))
+		return -EAGAIN;
+	return do_syslog(SYSLOG_ACTION_READ, buf, count, SYSLOG_FROM_PROC);
+}
+
+static __poll_t kmsg_poll(struct file *file, poll_table *wait)
+{
+	poll_wait(file, &log_wait, wait);
+	if (do_syslog(SYSLOG_ACTION_SIZE_UNREAD, NULL, 0, SYSLOG_FROM_PROC))
+		return EPOLLIN | EPOLLRDNORM;
+	return 0;
+}
+
+
+static const struct proc_ops kmsg_proc_ops = {
+	.proc_flags	= PROC_ENTRY_PERMANENT,
+	.proc_read	= kmsg_read,
+	.proc_poll	= kmsg_poll,
+	.proc_open	= kmsg_open,
+	.proc_release	= kmsg_release,
+	.proc_lseek	= generic_file_llseek,
+};
+
+static int __init proc_kmsg_init(void)
+{
+	proc_create("kmsg", S_IRUSR, NULL, &kmsg_proc_ops);
+	return 0;
+}
+fs_initcall(proc_kmsg_init);