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, 34 insertions, 0 deletions

diff --git a/Documentation/admin-guide/sysctl/abi.rst b/Documentation/admin-guide/sysctl/abi.rst
new file mode 100644
index 000000000..4e6db0a2a
--- /dev/null
+++ b/Documentation/admin-guide/sysctl/abi.rst
@@ -0,0 +1,34 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+================================
+Documentation for /proc/sys/abi/
+================================
+
+.. See scripts/check-sysctl-docs to keep this up to date:
+.. scripts/check-sysctl-docs -vtable="abi" \
+..         Documentation/admin-guide/sysctl/abi.rst \
+..         $(git grep -l register_sysctl_)
+
+Copyright (c) 2020, Stephen Kitt
+
+For general info, see Documentation/admin-guide/sysctl/index.rst.
+
+------------------------------------------------------------------------------
+
+The files in ``/proc/sys/abi`` can be used to see and modify
+ABI-related settings.
+
+Currently, these files might (depending on your configuration)
+show up in ``/proc/sys/kernel``:
+
+.. contents:: :local:
+
+vsyscall32 (x86)
+================
+
+Determines whether the kernels maps a vDSO page into 32-bit processes;
+can be set to 1 to enable, or 0 to disable. Defaults to enabled if
+``CONFIG_COMPAT_VDSO`` is set, disabled otherwise.
+
+This controls the same setting as the ``vdso32`` kernel boot
+parameter.