linux-kernel - Re: [PATCH 3/6] arm64/vdso: Add time napespace page

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Date:   Wed, 22 Apr 2020 22:23:57 -0700
From:   Andrei Vagin <avagin@...il.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Vincenzo Frascino <vincenzo.frascino@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Safonov <dima@...sta.com>
Subject: Re: [PATCH 3/6] arm64/vdso: Add time napespace page

On Thu, Apr 16, 2020 at 11:45:27AM +0100, Mark Rutland wrote:
> Hi Andrei,
> 
> On Wed, Apr 15, 2020 at 10:26:15PM -0700, Andrei Vagin wrote:
> > diff --git a/arch/arm64/include/asm/vdso.h b/arch/arm64/include/asm/vdso.h
> > index 07468428fd29..351c145d3808 100644
> > --- a/arch/arm64/include/asm/vdso.h
> > +++ b/arch/arm64/include/asm/vdso.h
...
> > +#ifdef CONFIG_TIME_NS
> > +static __always_inline const struct vdso_data *__arch_get_timens_vdso_data(void)
> > +{
> > +	const struct vdso_data *ret;
> > +
> > +	ret = _timens_data;
> > +	OPTIMIZER_HIDE_VAR(ret);
> > +
> > +	return ret;
> > +}
> > +#endif
> 
> Sorry for the confusion here, but please either:
> 
> * Add a preparatory patch making __arch_get_vdso_data() use
>   OPTIMIZER_HIDE_VAR(), and use OPTIMIZER_HIDE_VAR() here.
> 
> * Use the same assembly as __arch_get_vdso_data() currently does.
> 
> ... and either way add a comment here:
> 
> 	/* See __arch_get_vdso_data() */
> 
> ... so taht the rationale is obvious.
> 
> [...]
> 
> > +enum vvar_pages {
> > +	VVAR_DATA_PAGE_OFFSET = 0,
> > +#ifdef CONFIG_TIME_NS
> > +	VVAR_TIMENS_PAGE_OFFSET = 1,
> > +#endif /* CONFIG_TIME_NS */
> > +	VVAR_NR_PAGES = __VVAR_PAGES,
> > +};
> 
> Pet peeve, but we don't need the initializers here, as enums start from
> zero. The last element shouldn't have a trailing comma as we don't
> expect to add elements after it in future.
> 
> Rather than assigning to VVAR_NR_PAGES, it'd be better to use a
> BUILD_BUG_ON() to verify that it is the number we expect:
> 
> enum vvar_pages {
> 	VVAR_DATA_PAGE,
> #ifdef CONFIG_TIME_NS
> 	VVAR_TIMENS_PAGE,
> #endif
> 	VVAR_NR_PAGES
> };
> 
> BUILD_BUG_ON(VVAR_NR_PAGES != __VVAR_PAGES);

Hi Mark,

Thank you for the review. I have sent a fixed version of this patch in
replay to the origin patch.

Thanks,
Andrei