linux-kernel - Re: [PATCH RESEND v7 0/6] support FEAT_LSUI and apply it on futex atomic ops

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Message-ID: <aMh4_XzQqG2gZU_y@willie-the-truck>
Date: Mon, 15 Sep 2025 21:37:17 +0100
From: Will Deacon <will@...nel.org>
To: Catalin Marinas <catalin.marinas@....com>
Cc: Yeoreum Yun <yeoreum.yun@....com>, broonie@...nel.org, maz@...nel.org,
	oliver.upton@...ux.dev, joey.gouly@....com, james.morse@....com,
	ardb@...nel.org, scott@...amperecomputing.com,
	suzuki.poulose@....com, yuzenghui@...wei.com, mark.rutland@....com,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND v7 0/6] support FEAT_LSUI and apply it on futex
 atomic ops

On Thu, Sep 11, 2025 at 05:22:22PM +0100, Catalin Marinas wrote:
> On Thu, Sep 11, 2025 at 04:09:42PM +0100, Will Deacon wrote:
> > On Sat, Aug 16, 2025 at 04:19:23PM +0100, Yeoreum Yun wrote:
> > > Since Armv9.6, FEAT_LSUI supplies the load/store instructions for
> > > previleged level to access to access user memory without clearing
> > > PSTATE.PAN bit.
> > > 
> > > This patchset support FEAT_LSUI and applies in futex atomic operation
> > > where can replace from ldxr/stlxr pair implmentation with clearing
> > > PSTATE.PAN bit to correspondant load/store unprevileged atomic operation
> > > without clearing PSTATE.PAN bit.
> > > 
> > > (Sorry, I've sent wrongly for patch version 7 and resend it.
> > >  Again, sorry for mail-boom).
> > 
> > I tried to review this but I can't find any details about FEAT_LSUI in
> > the latest Arm ARM. Where should I be looking for the architecture spec?
> 
> Unfortunately, it's just in the public xml at the moment. Hopefully
> we'll get a release of the Arm ARM by the end of the year. Otherwise, in
> the private 2024 arch spec. Not ideal though.

Ah, thanks, the xml is a *lot* better than nothing.

> If you'd rather wait until in turns up in the public spec, fine by me.

As long as you're happy to continue helping with the review, I think
it's fine.

Cheers,

Will