linux-kernel - Re: [PATCH v4 0/7] Add managed SOFT RESERVE resource handling

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Message-ID: <e4f6c5ec-a91e-4396-b13a-aaf30d895ac5@fujitsu.com>
Date: Mon, 16 Jun 2025 01:00:38 +0000
From: "Zhijian Li (Fujitsu)" <lizhijian@...itsu.com>
To: "Koralahalli Channabasappa, Smita"
	<Smita.KoralahalliChannabasappa@....com>, "linux-cxl@...r.kernel.org"
	<linux-cxl@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "nvdimm@...ts.linux.dev"
	<nvdimm@...ts.linux.dev>, "linux-fsdevel@...r.kernel.org"
	<linux-fsdevel@...r.kernel.org>, "linux-pm@...r.kernel.org"
	<linux-pm@...r.kernel.org>
CC: Davidlohr Bueso <dave@...olabs.net>, Jonathan Cameron
	<jonathan.cameron@...wei.com>, Dave Jiang <dave.jiang@...el.com>, Alison
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	<jack@...e.cz>, "Rafael J . Wysocki" <rafael@...nel.org>, Len Brown
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 Huang <huang.ying.caritas@...il.com>, "Xingtao Yao (Fujitsu)"
	<yaoxt.fnst@...itsu.com>, Peter Zijlstra <peterz@...radead.org>, Greg KH
	<gregkh@...uxfoundation.org>, Nathan Fontenot <nathan.fontenot@....com>,
	Terry Bowman <terry.bowman@....com>, Robert Richter <rrichter@....com>,
	Benjamin Cheatham <benjamin.cheatham@....com>, PradeepVineshReddy Kodamati
	<PradeepVineshReddy.Kodamati@....com>
Subject: Re: [PATCH v4 0/7] Add managed SOFT RESERVE resource handling



On 05/06/2025 02:59, Koralahalli Channabasappa, Smita wrote:
>>
>>
>> To the CXL community,
>>
>> The scenarios mentioned here essentially cover what a correct firmware may provide. However,
>> I would like to discuss one more scenario that I can simulate with a modified QEMU:
>> The E820 exposes a SOFT RESERVED region which is the same as a CFMW, but the HDM decoders are not committed. This means no region will be auto-created during boot.
>>
>> As an example, after boot, the iomem tree is as follows:
>> 1050000000-304fffffff : CXL Window 0
>>     1050000000-304fffffff : Soft Reserved
>>       <No region>
>>
>> In this case, the SOFT RESERVED resource is not trimmed, so the end-user cannot create a new region.
>> My question is: Is this scenario a problem? If it is, should we fix it in this patchset or create a new patch?
>>
> 
> I believe firmware should handle this correctly by ensuring that any exposed SOFT RESERVED ranges correspond to committed HDM decoders and result in region creation.
> 
> That said, I’d be interested in hearing what the rest of the community thinks.


After several days, we still haven't heard other significant opinions. I'm fine with keeping the current case coverage.
If the case I described becomes common in the future, we can revisit it then.

Thanks
Zhijian