linux-kernel - Re: [RFC PATCH v2 1/2] ARM/mm/fault: always goto bad_area when handling with page faults of kernel address

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Message-ID: <aSndJ1EYUnMGsUYX@shell.armlinux.org.uk>
Date: Fri, 28 Nov 2025 17:34:31 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Xie Yuanbin <xieyuanbin1@...wei.com>, akpm@...ux-foundation.org,
	arnd@...db.de, brauner@...nel.org, david.laight@...box.com,
	hch@....de, jack@...e.com, kuninori.morimoto.gx@...esas.com,
	liaohua4@...wei.com, lilinjie8@...wei.com,
	linux-arm-kernel@...ts.infradead.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	lorenzo.stoakes@...cle.com, marc.zyngier@....com, nico@...xnic.net,
	pangliyuan1@...wei.com, pfalcato@...e.de, punitagrawal@...il.com,
	rjw@...ysocki.net, rppt@...nel.org, tony@...mide.com,
	vbabka@...e.cz, viro@...iv.linux.org.uk, wangkefeng.wang@...wei.com,
	will@...nel.org, wozizhi@...weicloud.com
Subject: Re: [RFC PATCH v2 1/2] ARM/mm/fault: always goto bad_area when
 handling with page faults of kernel address

On Fri, Nov 28, 2025 at 06:22:42PM +0100, Sebastian Andrzej Siewior wrote:
> On 2025-11-28 17:01:18 [+0000], Russell King (Oracle) wrote:
> > > I hope Russell will add them once he gets to it. They got reviewed, I
> > > added them to the patch system.
> > 
> > I'm not sure which patches you're talking about, but discussion is
> > still ongoing, so it would be greatly premature to merge anything.
> 
> This thread
> 	https://lore.kernel.org/all/20251110145555.2555055-1-bigeasy@linutronix.de/
> 
> and the patches are 9459/1 to 9463/1 in your patch system. They address
> other issues, not this one.

Oh, the branch predictor issue. Yea, I'm not keen on changing that
because I'm not sure if it's correct (the knowledge for this has
long since evaporated.) There have been multiple attempts at fixing
this in the past, and I've previously pointed out problems with
them when I _did_ have the knowledge. Have you looked back in the
archives to see whether any of that feedback I've given in the past
is relevant?

> > https://lore.kernel.org/r/aSmUnZZATTn3JD7m@willie-the-truck
> > 
> > There are now many threads each with their own discussion, which
> > makes it more difficult to work out which is the implementation that
> > should be merged. Clearly, not everyone knows about the other
> > discussion threads.
> 
> So Will suggested to let change the handler and handle this case. The
> other patch is avoiding handling addr > TASK_SIZE.
> Any preferences from your side?

... and now we have a new proposal from Linus. I'm not intending to
do anything on this new problem until the discussion calms down and
we stop getting new solutions.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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