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, 23 insertions, 0 deletions

diff --git a/Documentation/driver-api/wmi.rst b/Documentation/driver-api/wmi.rst
new file mode 100644
index 000000000..b847bcdcb
--- /dev/null
+++ b/Documentation/driver-api/wmi.rst
@@ -0,0 +1,23 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+==============
+WMI Driver API
+==============
+
+The WMI driver core supports a more modern bus-based interface for interacting
+with WMI devices, and an older GUID-based interface. The latter interface is
+considered to be deprecated, so new WMI drivers should generally avoid it since
+it has some issues with multiple WMI devices sharing the same GUID.
+The modern bus-based interface instead maps each WMI device to a
+:c:type:`struct wmi_device <wmi_device>`, so it supports WMI devices sharing the
+same GUID. Drivers can then register a :c:type:`struct wmi_driver <wmi_driver>`
+which will be bound to compatible WMI devices by the driver core.
+
+.. kernel-doc:: include/linux/wmi.h
+   :internal:
+
+.. kernel-doc:: drivers/platform/wmi/string.c
+   :export:
+
+.. kernel-doc:: drivers/platform/wmi/core.c
+   :export: