linux-kernel - Re: [PATCH v4 1/2] kasan/hw-tags: introduce kasan.write

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Message-ID: <CA+fCnZd9m3WBPimikuxSMNar-xbDaNFNQEJ9Bn=8uCMe-uYHeQ@mail.gmail.com>
Date: Mon, 18 Aug 2025 16:42:02 +0200
From: Andrey Konovalov <andreyknvl@...il.com>
To: Yeoreum Yun <yeoreum.yun@....com>
Cc: ryabinin.a.a@...il.com, glider@...gle.com, dvyukov@...gle.com, 
	vincenzo.frascino@....com, corbet@....net, catalin.marinas@....com, 
	will@...nel.org, akpm@...ux-foundation.org, scott@...amperecomputing.com, 
	jhubbard@...dia.com, pankaj.gupta@....com, leitao@...ian.org, 
	kaleshsingh@...gle.com, maz@...nel.org, broonie@...nel.org, 
	oliver.upton@...ux.dev, james.morse@....com, ardb@...nel.org, 
	hardevsinh.palaniya@...iconsignals.io, david@...hat.com, 
	yang@...amperecomputing.com, kasan-dev@...glegroups.com, 
	workflows@...r.kernel.org, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-mm@...ck.org
Subject: Re: [PATCH v4 1/2] kasan/hw-tags: introduce kasan.write_only option

On Mon, Aug 18, 2025 at 3:11 PM Yeoreum Yun <yeoreum.yun@....com> wrote:
>
> > > +           hw_enable_tag_checks_write_only()) {
> > > +               kasan_arg_write_only == KASAN_ARG_WRITE_ONLY_OFF;
> >
> > Typo in == in the line above. But also I think we can just drop the
> > line: kasan_arg_write_only is KASAN_ARG_WRITE_ONLY_ON after all, it's
> > just not supported and thus kasan_flag_write_only is set to false to
> > reflect that.
>
> Sorry :\ I've missed this fix from patch 3... this should be == to =.
>
> However, we couldn't remove kasan_arg_write_only check in condition.
> If one of cpu get failed to hw_enable_tag_checks_write_only() then
> By changing this with KASAN_ARG_WRITE_ONLY_OFF, It prevent to call
> hw_eanble_tag_checks_write_only() in other cpu.

Is it possible that the write-only mode will fail to be enabled on one
CPU but then get enabled successfully for another?

What would happen with the current code if the first CPU succeeds in
enabling the write-only mode, and the second one fails?

> As you said, kasan_flag_write_only reflects the state.
> But like other option, I keep the condition to call the hw_enable_xxx()
> by checking the "argments" and keep the "hw enable state" with
> kasan_flag_write_only.

Assuming we keep this behavior, please add a comment explaining all this.