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, 77 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-firmware b/Documentation/ABI/testing/sysfs-class-firmware
new file mode 100644
index 000000000..fba87a55f
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-firmware
@@ -0,0 +1,77 @@
+What: 		/sys/class/firmware/.../data
+Date:		July 2022
+KernelVersion:	5.19
+Contact:	Russ Weight <russ.weight@linux.dev>
+Description:	The data sysfs file is used for firmware-fallback and for
+		firmware uploads. Cat a firmware image to this sysfs file
+		after you echo 1 to the loading sysfs file. When the firmware
+		image write is complete, echo 0 to the loading sysfs file. This
+		sequence will signal the completion of the firmware write and
+		signal the lower-level driver that the firmware data is
+		available.
+
+What: 		/sys/class/firmware/.../cancel
+Date:		July 2022
+KernelVersion:	5.19
+Contact:	Russ Weight <russ.weight@linux.dev>
+Description:	Write-only. For firmware uploads, write a "1" to this file to
+		request that the transfer of firmware data to the lower-level
+		device be canceled. This request will be rejected (EBUSY) if
+		the update cannot be canceled (e.g. a FLASH write is in
+		progress) or (ENODEV) if there is no firmware update in progress.
+
+What: 		/sys/class/firmware/.../error
+Date:		July 2022
+KernelVersion:	5.19
+Contact:	Russ Weight <russ.weight@linux.dev>
+Description:	Read-only. Returns a string describing a failed firmware
+		upload. This string will be in the form of <STATUS>:<ERROR>,
+		where <STATUS> will be one of the status strings described
+		for the status sysfs file and <ERROR> will be one of the
+		following: "hw-error", "timeout", "user-abort", "device-busy",
+		"invalid-file-size", "read-write-error", "flash-wearout". The
+		error sysfs file is only meaningful when the current firmware
+		upload status is "idle". If this file is read while a firmware
+		transfer is in progress, then the read will fail with EBUSY.
+
+What: 		/sys/class/firmware/.../loading
+Date:		July 2022
+KernelVersion:	5.19
+Contact:	Russ Weight <russ.weight@linux.dev>
+Description:	The loading sysfs file is used for both firmware-fallback and
+		for firmware uploads. Echo 1 onto the loading file to indicate
+		you are writing a firmware file to the data sysfs node. Echo
+		-1 onto this file to abort the data write or echo 0 onto this
+		file to indicate that the write is complete. For firmware
+		uploads, the zero value also triggers the transfer of the
+		firmware data to the lower-level device driver.
+
+What: 		/sys/class/firmware/.../remaining_size
+Date:		July 2022
+KernelVersion:	5.19
+Contact:	Russ Weight <russ.weight@linux.dev>
+Description:	Read-only. For firmware upload, this file contains the size
+		of the firmware data that remains to be transferred to the
+		lower-level device driver. The size value is initialized to
+		the full size of the firmware image that was previously
+		written to the data sysfs file. This value is periodically
+		updated during the "transferring" phase of the firmware
+		upload.
+		Format: "%u".
+
+What: 		/sys/class/firmware/.../status
+Date:		July 2022
+KernelVersion:	5.19
+Contact:	Russ Weight <russ.weight@linux.dev>
+Description:	Read-only. Returns a string describing the current status of
+		a firmware upload. The string will be one of the following:
+		idle, "receiving", "preparing", "transferring", "programming".
+
+What: 		/sys/class/firmware/.../timeout
+Date:		July 2022
+KernelVersion:	5.19
+Contact:	Russ Weight <russ.weight@linux.dev>
+Description:	This file supports the timeout mechanism for firmware
+		fallback.  This file has no affect on firmware uploads. For
+		more information on timeouts please see the documentation
+		for firmware fallback.