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, 142 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-ptp b/Documentation/ABI/testing/sysfs-ptp
new file mode 100644
index 000000000..9c317ac7c
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-ptp
@@ -0,0 +1,142 @@
+What:		/sys/class/ptp/
+Date:		September 2010
+Contact:	Richard Cochran <richardcochran@gmail.com>
+Description:
+		This directory contains files and directories
+		providing a standardized interface to the ancillary
+		features of PTP hardware clocks.
+
+What:		/sys/class/ptp/ptp<N>/
+Date:		September 2010
+Contact:	Richard Cochran <richardcochran@gmail.com>
+Description:
+		This directory contains the attributes of the Nth PTP
+		hardware clock registered into the PTP class driver
+		subsystem.
+
+What:		/sys/class/ptp/ptp<N>/clock_name
+Date:		September 2010
+Contact:	Richard Cochran <richardcochran@gmail.com>
+Description:
+		This file contains the name of the PTP hardware clock
+		as a human readable string. The purpose of this
+		attribute is to provide the user with a "friendly
+		name" and to help distinguish PHY based devices from
+		MAC based ones. The string does not necessarily have
+		to be any kind of unique id.
+
+What:		/sys/class/ptp/ptp<N>/max_adjustment
+Date:		September 2010
+Contact:	Richard Cochran <richardcochran@gmail.com>
+Description:
+		This file contains the PTP hardware clock's maximum
+		frequency adjustment value (a positive integer) in
+		parts per billion.
+
+What:		/sys/class/ptp/ptp<N>/max_vclocks
+Date:		May 2021
+Contact:	Yangbo Lu <yangbo.lu@nxp.com>
+Description:
+		This file contains the maximum number of ptp vclocks.
+		Write integer to re-configure it.
+
+What:		/sys/class/ptp/ptp<N>/n_alarms
+Date:		September 2010
+Contact:	Richard Cochran <richardcochran@gmail.com>
+Description:
+		This file contains the number of periodic or one shot
+		alarms offer by the PTP hardware clock.
+
+What:		/sys/class/ptp/ptp<N>/n_external_timestamps
+Date:		September 2010
+Contact:	Richard Cochran <richardcochran@gmail.com>
+Description:
+		This file contains the number of external timestamp
+		channels offered by the PTP hardware clock.
+
+What:		/sys/class/ptp/ptp<N>/n_periodic_outputs
+Date:		September 2010
+Contact:	Richard Cochran <richardcochran@gmail.com>
+Description:
+		This file contains the number of programmable periodic
+		output channels offered by the PTP hardware clock.
+
+What:		/sys/class/ptp/ptp<N>/n_pins
+Date:		March 2014
+Contact:	Richard Cochran <richardcochran@gmail.com>
+Description:
+		This file contains the number of programmable pins
+		offered by the PTP hardware clock.
+
+What:		/sys/class/ptp/ptp<N>/n_vclocks
+Date:		May 2021
+Contact:	Yangbo Lu <yangbo.lu@nxp.com>
+Description:
+		This file contains the number of virtual PTP clocks in
+		use.  By default, the value is 0 meaning that only the
+		physical clock is in use.  Setting the value creates
+		the corresponding number of virtual clocks and causes
+		the physical clock to become free running.  Setting the
+		value back to 0 deletes the virtual clocks and
+		switches the physical clock back to normal, adjustable
+		operation.
+
+What:		/sys/class/ptp/ptp<N>/pins
+Date:		March 2014
+Contact:	Richard Cochran <richardcochran@gmail.com>
+Description:
+		This directory contains one file for each programmable
+		pin offered by the PTP hardware clock. The file name
+		is the hardware dependent pin name. Reading from this
+		file produces two numbers, the assigned function (see
+		the `PTP_PF_` enumeration values in linux/ptp_clock.h)
+		and the channel number. The function and channel
+		assignment may be changed by two writing numbers into
+		the file.
+
+What:		/sys/class/ptp/ptp<N>/pps_available
+Date:		September 2010
+Contact:	Richard Cochran <richardcochran@gmail.com>
+Description:
+		This file indicates whether the PTP hardware clock
+		supports a Pulse Per Second to the host CPU. Reading
+		"1" means that the PPS is supported, while "0" means
+		not supported.
+
+What:		/sys/class/ptp/ptp<N>/extts_enable
+Date:		September 2010
+Contact:	Richard Cochran <richardcochran@gmail.com>
+Description:
+		This write-only file enables or disables external
+		timestamps. To enable external timestamps, write the
+		channel index followed by a "1" into the file.
+		To disable external timestamps, write the channel
+		index followed by a "0" into the file.
+
+What:		/sys/class/ptp/ptp<N>/fifo
+Date:		September 2010
+Contact:	Richard Cochran <richardcochran@gmail.com>
+Description:
+		This file provides timestamps on external events, in
+		the form of three integers: channel index, seconds,
+		and nanoseconds.
+
+What:		/sys/class/ptp/ptp<N>/period
+Date:		September 2010
+Contact:	Richard Cochran <richardcochran@gmail.com>
+Description:
+		This write-only file enables or disables periodic
+		outputs. To enable a periodic output, write five
+		integers into the file: channel index, start time
+		seconds, start time nanoseconds, period seconds, and
+		period nanoseconds. To disable a periodic output, set
+		all the seconds and nanoseconds values to zero.
+
+What:		/sys/class/ptp/ptp<N>/pps_enable
+Date:		September 2010
+Contact:	Richard Cochran <richardcochran@gmail.com>
+Description:
+		This write-only file enables or disables delivery of
+		PPS events to the Linux PPS subsystem. To enable PPS
+		events, write a "1" into the file. To disable events,
+		write a "0" into the file.