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, 74 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-edac-ecs b/Documentation/ABI/testing/sysfs-edac-ecs
new file mode 100644
index 000000000..87c885c4e
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-edac-ecs
@@ -0,0 +1,74 @@
+What:		/sys/bus/edac/devices/<dev-name>/ecs_fruX
+Date:		March 2025
+KernelVersion:	6.15
+Contact:	linux-edac@vger.kernel.org
+Description:
+		The sysfs EDAC bus devices /<dev-name>/ecs_fruX subdirectory
+		pertains to the memory media ECS (Error Check Scrub) control
+		feature, where <dev-name> directory corresponds to a device
+		registered with the EDAC device driver for the ECS feature.
+		/ecs_fruX belongs to the media FRUs (Field Replaceable Unit)
+		under the memory device.
+
+		The sysfs ECS attr nodes are only present if the parent
+		driver has implemented the corresponding attr callback
+		function and provided the necessary operations to the EDAC
+		device driver during registration.
+
+What:		/sys/bus/edac/devices/<dev-name>/ecs_fruX/log_entry_type
+Date:		March 2025
+KernelVersion:	6.15
+Contact:	linux-edac@vger.kernel.org
+Description:
+		(RW) The log entry type of how the DDR5 ECS log is reported.
+
+		- 0 - per DRAM.
+
+		- 1 - per memory media FRU.
+
+		- All other values are reserved.
+
+What:		/sys/bus/edac/devices/<dev-name>/ecs_fruX/mode
+Date:		March 2025
+KernelVersion:	6.15
+Contact:	linux-edac@vger.kernel.org
+Description:
+		(RW) The mode of how the DDR5 ECS counts the errors.
+		Error count is tracked based on two different modes
+		selected by DDR5 ECS Control Feature - Codeword mode and
+		Row Count mode. If the ECS is under Codeword mode, then
+		the error count increments each time a codeword with check
+		bit errors is detected. If the ECS is under Row Count mode,
+		then the error counter increments each time a row with
+		check bit errors is detected.
+
+		- 0 - ECS counts rows in the memory media that have ECC errors.
+
+		- 1 - ECS counts codewords with errors, specifically, it counts
+		      the number of ECC-detected errors in the memory media.
+
+		- All other values are reserved.
+
+What:		/sys/bus/edac/devices/<dev-name>/ecs_fruX/reset
+Date:		March 2025
+KernelVersion:	6.15
+Contact:	linux-edac@vger.kernel.org
+Description:
+		(WO) ECS reset ECC counter.
+
+		- 1 - reset ECC counter to the default value.
+
+		- All other values are reserved.
+
+What:		/sys/bus/edac/devices/<dev-name>/ecs_fruX/threshold
+Date:		March 2025
+KernelVersion:	6.15
+Contact:	linux-edac@vger.kernel.org
+Description:
+		(RW) DDR5 ECS threshold count per gigabits of memory cells.
+		The ECS error count is subject to the ECS Threshold count
+		per Gbit, which masks error counts less than the Threshold.
+
+		Supported values are 256, 1024 and 4096.
+
+		All other values are reserved.