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, 70 insertions, 0 deletions

diff --git a/Documentation/admin-guide/mono.rst b/Documentation/admin-guide/mono.rst
new file mode 100644
index 000000000..c6dab5680
--- /dev/null
+++ b/Documentation/admin-guide/mono.rst
@@ -0,0 +1,70 @@
+Mono(tm) Binary Kernel Support for Linux
+-----------------------------------------
+
+To configure Linux to automatically execute Mono-based .NET binaries
+(in the form of .exe files) without the need to use the mono CLR
+wrapper, you can use the BINFMT_MISC kernel support.
+
+This will allow you to execute Mono-based .NET binaries just like any
+other program after you have done the following:
+
+1) You MUST FIRST install the Mono CLR support, either by downloading
+   a binary package, a source tarball or by installing from Git. Binary
+   packages for several distributions can be found at:
+
+	https://www.mono-project.com/download/
+
+   Instructions for compiling Mono can be found at:
+
+	https://www.mono-project.com/docs/compiling-mono/linux/
+
+   Once the Mono CLR support has been installed, just check that
+   ``/usr/bin/mono`` (which could be located elsewhere, for example
+   ``/usr/local/bin/mono``) is working.
+
+2) You have to compile BINFMT_MISC either as a module or into
+   the kernel (``CONFIG_BINFMT_MISC``) and set it up properly.
+   If you choose to compile it as a module, you will have
+   to insert it manually with modprobe/insmod, as kmod
+   cannot be easily supported with binfmt_misc.
+   Read the file ``binfmt_misc.txt`` in this directory to know
+   more about the configuration process.
+
+3) Add the following entries to ``/etc/rc.local`` or similar script
+   to be run at system startup:
+
+   .. code-block:: sh
+
+    # Insert BINFMT_MISC module into the kernel
+    if [ ! -e /proc/sys/fs/binfmt_misc/register ]; then
+        /sbin/modprobe binfmt_misc
+	# Some distributions, like Fedora Core, perform
+	# the following command automatically when the
+	# binfmt_misc module is loaded into the kernel
+	# or during normal boot up (systemd-based systems).
+	# Thus, it is possible that the following line
+	# is not needed at all.
+	mount -t binfmt_misc none /proc/sys/fs/binfmt_misc
+    fi
+
+    # Register support for .NET CLR binaries
+    if [ -e /proc/sys/fs/binfmt_misc/register ]; then
+	# Replace /usr/bin/mono with the correct pathname to
+	# the Mono CLR runtime (usually /usr/local/bin/mono
+	# when compiling from sources or CVS).
+        echo ':CLR:M::MZ::/usr/bin/mono:' > /proc/sys/fs/binfmt_misc/register
+    else
+        echo "No binfmt_misc support"
+        exit 1
+    fi
+
+4) Check that ``.exe`` binaries can be ran without the need of a
+   wrapper script, simply by launching the ``.exe`` file directly
+   from a command prompt, for example::
+
+	/usr/bin/xsd.exe
+
+   .. note::
+
+      If this fails with a permission denied error, check
+      that the ``.exe`` file has execute permissions.