linux-kernel - Re: [PATCH v15 11/15] EDAC: Add memory repair control feature

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Message-ID: <20241114133249.GEZzX8ATNyc_Xw1L52@fat_crate.local>
Date: Thu, 14 Nov 2024 14:32:49 +0100
From: Borislav Petkov <bp@...en8.de>
To: Shiju Jose <shiju.jose@...wei.com>
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Subject: Re: [PATCH v15 11/15] EDAC: Add memory repair control feature

On Mon, Nov 11, 2024 at 04:54:48PM +0000, Shiju Jose wrote:
> Presently, 0 (soft memory repair) and 1 (hard memory repair),  depends on
> which mode/s a memory device is supported. 

What if the device supports more than one mode?

> However for CXL memory sparing feature, the persistent mode is configurable at runtime
> for a memory sparing instance, thus both soft and hard sparing are supported.
> Example given for CXL memory sparing feature in Documentation/edac/memory_repair.rst,
> root@...alhost:~# cat /sys/bus/edac/devices/cxl_mem0/mem_repair1/persist_mode_avail
> 0,1

Ok, and how is the user supposed to know what those mean?

> Kernel sysfs doc mentioned about array of values as follows, though not seen much examples. 
> https://docs.kernel.org/filesystems/sysfs.html
> "Attributes should be ASCII text files, preferably with only one value per file. It is noted that
> it may not be efficient to contain only one value per file, so it is socially acceptable to express
> an array of values of the same type."

True story. Ok, so there's an exception to that rule.

> The values of these attributes are specific to device and portion of the memory to repair. 
> For example, In CXL repair features,
> CXL memory device identifies a failure on a memory component, device provides the corresponding
> values of the attributes (DPA, channel, rank, nibble mask, bank group, bank, row, column or sub-channel etc)
> in an event record to the host and to the userspace in the corresponding trace event.  
> Userspace shall use these values for the query resource availability and repair operations.

I don't think you're answering my question. Lemme try again:

I am on a machine with such an interface. I do

echo 0xdeadbeef > /sys/devices...
-EINVAL

echo 0xface > ...
-EINVAL

How do I know what the allowed ranges are?

> This will work for the CXL PPR feature where the result of the query operation for resources  availability
> return to the command, however for the CXL memory sparing features,  the result of the query resources 
> availability command returned later in a Memory Sparing Event Record from the device. 
> Userspace shall issue repair operation with the attributes values received on the Memory Sparing trace event.
> Thus for the CXL memory sparing feature, query for resources availability and repair operation 
> cannot be combined.

What happens if the resources availability changes between the query and the
start of the repair operation?

The cat catches fire?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette