linux-kernel - Re: [PATCH v4 1/9] dax/hmem, e820, resource: Defer Soft Reserved insertion until hmem is ready

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Message-ID: <69433a20ce302_1cf51004c@dwillia2-mobl4.notmuch>
Date: Wed, 17 Dec 2025 15:17:52 -0800
From: <dan.j.williams@...el.com>
To: "Koralahalli Channabasappa, Smita" <skoralah@....com>,
	<dan.j.williams@...el.com>, Smita Koralahalli
	<Smita.KoralahalliChannabasappa@....com>, <linux-cxl@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <nvdimm@...ts.linux.dev>,
	<linux-fsdevel@...r.kernel.org>, <linux-pm@...r.kernel.org>
CC: Alison Schofield <alison.schofield@...el.com>, Vishal Verma
	<vishal.l.verma@...el.com>, Ira Weiny <ira.weiny@...el.com>, Jonathan Cameron
	<jonathan.cameron@...wei.com>, Yazen Ghannam <yazen.ghannam@....com>, "Dave
 Jiang" <dave.jiang@...el.com>, Davidlohr Bueso <dave@...olabs.net>, "Matthew
 Wilcox" <willy@...radead.org>, Jan Kara <jack@...e.cz>, "Rafael J . Wysocki"
	<rafael@...nel.org>, Len Brown <len.brown@...el.com>, Pavel Machek
	<pavel@...nel.org>, Li Ming <ming.li@...omail.com>, Jeff Johnson
	<jeff.johnson@....qualcomm.com>, Ying Huang <huang.ying.caritas@...il.com>,
	Yao Xingtao <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>,
	Zhijian Li <lizhijian@...itsu.com>, Borislav Petkov <bp@...en8.de>, "Ard
 Biesheuvel" <ardb@...nel.org>
Subject: Re: [PATCH v4 1/9] dax/hmem, e820, resource: Defer Soft Reserved
 insertion until hmem is ready

Koralahalli Channabasappa, Smita wrote:
> Hi,
> 
> Sorry for the delay here. I was on vacation. Responses inline.
> 
> On 12/2/2025 2:19 PM, dan.j.williams@...el.com wrote:
> > Smita Koralahalli wrote:
> >> From: Dan Williams <dan.j.williams@...el.com>
> >>
> >> Insert Soft Reserved memory into a dedicated soft_reserve_resource tree
> >> instead of the iomem_resource tree at boot. Delay publishing these ranges
> >> into the iomem hierarchy until ownership is resolved and the HMEM path
> >> is ready to consume them.
> >>
> >> Publishing Soft Reserved ranges into iomem too early conflicts with CXL
> >> hotplug and prevents region assembly when those ranges overlap CXL
> >> windows.
> >>
> >> Follow up patches will reinsert Soft Reserved ranges into iomem after CXL
> >> window publication is complete and HMEM is ready to claim the memory. This
> >> provides a cleaner handoff between EFI-defined memory ranges and CXL
> >> resource management without trimming or deleting resources later.
> > 
> > Please, when you modify a patch from an original, add your
> > Co-developed-by: and clarify what you changed.
> 
> Thanks Dan. Yeah, this was a bit of a gray area for me. I had the
> impression or remember reading somewhere that Co-developed-by tags are
> typically added only when the modifications are substantial, so I didn’t
> include it initially. I will add the Co-developed-by: line.

Yes, there are no hard and fast rules here. My expectation is that if
you make any changes to a patch that change its "git patch-id" result,
then add Co-developed-by. If you make "substantial" modifcations then
consider taking Authorship and move the original Author to
Co-developed-by.

[..]
> >> +void insert_resource_expand_to_fit(struct resource *new)
> >> +{
> >> +	struct resource *root = &iomem_resource;
> >> +
> >> +#ifdef CONFIG_EFI_SOFT_RESERVE
> >> +	if (new->desc == IORES_DESC_SOFT_RESERVED)
> >> +		root = &soft_reserve_resource;
> >> +#endif
> > 
> > I can not say I am entirely happy with this change, I would prefer to
> > avoid ifdef in C, and I would prefer not to break the legacy semantics
> > of this function, but it meets the spirit of the original RFC without
> > introducing a new insert_resource_late(). I assume review feedback
> > requested this?
> 
> Yeah here, 
> https://lore.kernel.org/all/20250909161210.GBaMBR2rN8h6eT9JHe@fat_crate.local/

Thanks, I will go reply there.