linux-kernel - Re: [PATCH 0/4] apply page shift to PFN instead of VA in pfn_to

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Date: Fri, 2 Feb 2024 09:02:54 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Arnd Bergmann <arnd@...db.de>
CC: Linus Walleij <linus.walleij@...aro.org>, guoren <guoren@...nel.org>,
	Brian Cain <bcain@...cinc.com>, Jonas Bonn <jonas@...thpole.se>, "Stefan
 Kristiansson" <stefan.kristiansson@...nalahti.fi>, Stafford Horne
	<shorne@...il.com>, Linux-Arch <linux-arch@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, "linux-csky@...r.kernel.org"
	<linux-csky@...r.kernel.org>, <linux-hexagon@...r.kernel.org>,
	"linux-openrisc@...r.kernel.org" <linux-openrisc@...r.kernel.org>
Subject: Re: [PATCH 0/4] apply page shift to PFN instead of VA in pfn_to_virt

On Thu, Feb 01, 2024 at 06:46:46AM +0100, Arnd Bergmann wrote:
> On Thu, Feb 1, 2024, at 01:01, Yan Zhao wrote:
> > On Wed, Jan 31, 2024 at 12:48:38PM +0100, Arnd Bergmann wrote:
> >> On Wed, Jan 31, 2024, at 06:51, Yan Zhao wrote:
> >> 
> >> How exactly did you notice the function being wrong,
> >> did you try to add a user somewhere, or just read through
> >> the code?
> > I came across them when I was debugging an unexpected kernel page fault
> > on x86, and I was not sure whether page_to_virt() was compiled in
> > asm-generic/page.h or linux/mm.h.
> > Though finally, it turned out that the one in linux/mm.h was used, which
> > yielded the right result and the unexpected kernel page fault in my case
> > was not related to page_to_virt(), it did lead me to noticing that the
> > pfn_to_virt() in asm-generic/page.h and other 3 archs did not look right.
> >
> > Yes, unlike virt_to_pfn() which still has a caller in openrisc (among
> > csky, Hexagon, openrisc), pfn_to_virt() now does not have a caller in
> > the 3 archs. Though both virt_to_pfn() and pfn_to_virt() are referenced
> > in asm-generic/page.h, I also not sure if we need to remove the
> > asm-generic/page.h which may serve as a template to future archs ?
> >
> > So, either way looks good to me :)
> 
> I think it's fair to assume we won't need asm-generic/page.h any
> more, as we likely won't be adding new NOMMU architectures.
> I can have a look myself at removing any such unused headers in
> include/asm-generic/, it's probably not the only one.
> 
> Can you just send a patch to remove the unused pfn_to_virt()
> functions?
Ok. I'll do it!
BTW: do you think it's also good to keep this fixing series though we'll
remove the unused function later?
So if people want to revert the removal some day, they can get right one.

Or maybe I'm just paranoid, and explanation about the fix in the commit
message of patch for function removal is enough.

What's your preference? :)