linux-kernel - Re: [PATCH v7 1/2] kasan/hw-tags: introduce kasan.write

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Message-ID: <aMnbDcPMPvKXG7k+@e129823.arm.com>
Date: Tue, 16 Sep 2025 22:47:57 +0100
From: Yeoreum Yun <yeoreum.yun@....com>
To: Will Deacon <will@...nel.org>
Cc: ryabinin.a.a@...il.com, glider@...gle.com, andreyknvl@...il.com,
	dvyukov@...gle.com, vincenzo.frascino@....com, corbet@....net,
	catalin.marinas@....com, akpm@...ux-foundation.org,
	scott@...amperecomputing.com, jhubbard@...dia.com,
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	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,
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	linux-mm@...ck.org
Subject: Re: [PATCH v7 1/2] kasan/hw-tags: introduce kasan.write_only option

Hi, Will

> On Tue, Sep 16, 2025 at 09:19:30PM +0100, Yeoreum Yun wrote:
> > > On Wed, Sep 03, 2025 at 04:00:19PM +0100, Yeoreum Yun wrote:
> > > > +	switch (kasan_arg_write_only) {
> > > > +	case KASAN_ARG_WRITE_ONLY_DEFAULT:
> > > > +		/* Default is specified by kasan_flag_write_only definition. */
> > > > +		break;
> > > > +	case KASAN_ARG_WRITE_ONLY_OFF:
> > > > +		kasan_flag_write_only = false;
> > > > +		break;
> > > > +	case KASAN_ARG_WRITE_ONLY_ON:
> > > > +		kasan_flag_write_only = true;
> > > > +		break;
> > > > +	}
> > > > +
> > > >  	kasan_init_tags();
> > >
> > > I'm probably missing something here, but why have 'enum
> > > kasan_arg_write_only' at all? What stops you from setting
> > > 'kasan_flag_write_only' directly from early_kasan_flag_write_only()?
> > >
> > > This all looks weirdly over-engineered, as though 'kasan_flag_write_only'
> > > is expected to be statically initialised to something other than 'false'.
> >
> > For the conherent pattern for other options.
> > Since other options manage arg value and internal state separately,
> > I just followed former ancestor.
>
> I'm not sure it's the best option to blindly follow the existing code
> here. To pick another kasan "mode" at random, 'kasan_flag_vmalloc' is
> initialised differently depending on CONFIG_KASAN_VMALLOC and so
> allowing for the default value to differ based on the kernel
> configuration makes sense.
>
> But that doesn't apply here.
>
> I'd recommend starting simple and just having the 'flag', especially as
> you already made a small mistake because of mixing up the 'flag' with
> the 'arg'.

Okay. I'll change this.
Thanks.

--
Sincerely,
Yeoreum Yun