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, 129 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-watchdog b/Documentation/ABI/testing/sysfs-class-watchdog
new file mode 100644
index 000000000..70eabccf0
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-watchdog
@@ -0,0 +1,129 @@
+What:		/sys/class/watchdog/watchdogn/bootstatus
+Date:		August 2015
+Contact:	Wim Van Sebroeck <wim@iguana.be>
+Description:
+		It is a read only file. It contains status of the watchdog
+		device at boot. It is equivalent to WDIOC_GETBOOTSTATUS of
+		ioctl interface.
+
+What:		/sys/class/watchdog/watchdogn/options
+Date:		April 2023
+Contact:	Thomas Weißschuh
+Description:
+		It is a read only file. It contains options of watchdog device.
+
+What:		/sys/class/watchdog/watchdogn/fw_version
+Date:		April 2023
+Contact:	Thomas Weißschuh
+Description:
+		It is a read only file. It contains firmware version of
+		watchdog device.
+
+What:		/sys/class/watchdog/watchdogn/identity
+Date:		August 2015
+Contact:	Wim Van Sebroeck <wim@iguana.be>
+Description:
+		It is a read only file. It contains identity string of
+		watchdog device.
+
+What:		/sys/class/watchdog/watchdogn/nowayout
+Date:		August 2015
+Contact:	Wim Van Sebroeck <wim@iguana.be>
+Description:
+		It is a read/write file. While reading, it gives '1'
+		if the device has the nowayout feature set, otherwise
+		it gives '0'. Writing a '1' to the file enables the
+		nowayout feature. Once set, the nowayout feature
+		cannot be disabled, so writing a '0' either has no
+		effect (if the feature was already disabled) or
+		results in a permission error.
+
+What:		/sys/class/watchdog/watchdogn/state
+Date:		August 2015
+Contact:	Wim Van Sebroeck <wim@iguana.be>
+Description:
+		It is a read only file. It gives active/inactive status of
+		watchdog device.
+
+What:		/sys/class/watchdog/watchdogn/status
+Date:		August 2015
+Contact:	Wim Van Sebroeck <wim@iguana.be>
+Description:
+		It is a read only file. It contains watchdog device's
+		internal status bits. It is equivalent to WDIOC_GETSTATUS
+		of ioctl interface.
+
+What:		/sys/class/watchdog/watchdogn/timeleft
+Date:		August 2015
+Contact:	Wim Van Sebroeck <wim@iguana.be>
+Description:
+		It is a read only file. It contains value of time left for
+		reset generation. It is equivalent to WDIOC_GETTIMELEFT of
+		ioctl interface.
+
+What:		/sys/class/watchdog/watchdogn/timeout
+Date:		August 2015
+Contact:	Wim Van Sebroeck <wim@iguana.be>
+Description:
+		It is a read only file. It is read to know about current
+		value of timeout programmed.
+
+What:		/sys/class/watchdog/watchdogn/pretimeout
+Date:		December 2016
+Contact:	Wim Van Sebroeck <wim@iguana.be>
+Description:
+		It is a read only file. It specifies the time in seconds before
+		timeout when the pretimeout interrupt is delivered.  Pretimeout
+		is an optional feature.
+
+What:		/sys/class/watchdog/watchdogn/pretimeout_available_governors
+Date:		February 2017
+Contact:	Wim Van Sebroeck <wim@iguana.be>
+Description:
+		It is a read only file. It shows the pretimeout governors
+		available for this watchdog.
+
+What:		/sys/class/watchdog/watchdogn/pretimeout_governor
+Date:		February 2017
+Contact:	Wim Van Sebroeck <wim@iguana.be>
+Description:
+		It is a read/write file. When read, the currently assigned
+		pretimeout governor is returned.  When written, it sets
+		the pretimeout governor.
+
+What:		/sys/class/watchdog/watchdog1/access_cs0
+Date:		August 2019
+Contact:	Ivan Mikhaylov <i.mikhaylov@yadro.com>,
+		Alexander Amelkin <a.amelkin@yadro.com>
+Description:
+		It is a read/write file. This attribute exists only if the
+		system has booted from the alternate flash chip due to
+		expiration of a watchdog timer of AST2400/AST2500 when
+		alternate boot function was enabled with 'aspeed,alt-boot'
+		devicetree option for that watchdog or with an appropriate
+		h/w strapping (for WDT2 only).
+
+		At alternate flash the 'access_cs0' sysfs node provides:
+
+			ast2400:
+				a way to get access to the primary SPI flash
+				chip at CS0 after booting from the alternate
+				chip at CS1.
+			ast2500:
+				a way to restore the normal address mapping
+				from (CS0->CS1, CS1->CS0) to (CS0->CS0,
+				CS1->CS1).
+
+		Clearing the boot code selection and timeout counter also
+		resets to the initial state the chip select line mapping. When
+		the SoC is in normal mapping state (i.e. booted from CS0),
+		clearing those bits does nothing for both versions of the SoC.
+		For alternate boot mode (booted from CS1 due to wdt2
+		expiration) the behavior differs as described above.
+
+		This option can be used with wdt2 (watchdog1) only.
+
+		When read, the current status of the boot code selection is
+		shown. When written with any non-zero value, it clears
+		the boot code selection and the timeout counter, which results
+		in chipselect reset for AST2400/AST2500.