linux-kernel - Re: [PATCH 2/3] arm64: remove uaccess_ttbr0 asm macros from cache functions

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Date:   Wed, 4 Dec 2019 15:50:15 -0500
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     James Morris <jmorris@...ei.org>, Sasha Levin <sashal@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, steve.capper@....com,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Marc Zyngier <marc.zyngier@....com>,
        James Morse <james.morse@....com>,
        Vladimir Murzin <vladimir.murzin@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        allison@...utok.net, info@...ux.net, alexios.zavras@...el.com,
        Stefano Stabellini <sstabellini@...nel.org>,
        boris.ostrovsky@...cle.com, jgross@...e.com,
        Stefan Agner <stefan@...er.ch>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        xen-devel@...ts.xenproject.org,
        Russell King - ARM Linux admin <linux@...linux.org.uk>
Subject: Re: [PATCH 2/3] arm64: remove uaccess_ttbr0 asm macros from cache functions

On Thu, Nov 28, 2019 at 9:51 AM Mark Rutland <mark.rutland@....com> wrote:
>
> On Wed, Nov 27, 2019 at 01:44:52PM -0500, Pavel Tatashin wrote:
> > We currently duplicate the logic to enable/disable uaccess via TTBR0,
> > with C functions and assembly macros. This is a maintenenace burden
> > and is liable to lead to subtle bugs, so let's get rid of the assembly
> > macros, and always use the C functions. This requires refactoring
> > some assembly functions to have a C wrapper.
>
> [...]
>
> > +static inline int invalidate_icache_range(unsigned long start,
> > +                                       unsigned long end)
> > +{
> > +     int rv;
>
> Please make this 'ret', for consistency with other arm64 code. We only
> use 'rv' in one place where it's short for "Revision and Variant", and
> 'ret' is our usual name for a temporary variable used to hold a return
> value.

OK

>
> > +
> > +     if (cpus_have_const_cap(ARM64_HAS_CACHE_DIC)) {
> > +             isb();
> > +             return 0;
> > +     }
> > +     uaccess_ttbr0_enable();
>
> Please place a newline between these two, for consistency with other
> arm64 code.

OK

>
> > +     rv = asm_invalidate_icache_range(start, end);
> > +     uaccess_ttbr0_disable();
> > +
> > +     return rv;
> > +}
> > +
> >  static inline void flush_icache_range(unsigned long start, unsigned long end)
> >  {
> >       __flush_icache_range(start, end);
> > diff --git a/arch/arm64/mm/cache.S b/arch/arm64/mm/cache.S
> > index db767b072601..a48b6dba304e 100644
> > --- a/arch/arm64/mm/cache.S
> > +++ b/arch/arm64/mm/cache.S
> > @@ -15,7 +15,7 @@
> >  #include <asm/asm-uaccess.h>
> >
> >  /*
> > - *   flush_icache_range(start,end)
> > + *   __asm_flush_icache_range(start,end)
> >   *
> >   *   Ensure that the I and D caches are coherent within specified region.
> >   *   This is typically used when code has been written to a memory region,
> > @@ -24,11 +24,11 @@
> >   *   - start   - virtual start address of region
> >   *   - end     - virtual end address of region
> >   */
> > -ENTRY(__flush_icache_range)
> > +ENTRY(__asm_flush_icache_range)
> >       /* FALLTHROUGH */
> >
> >  /*
> > - *   __flush_cache_user_range(start,end)
> > + *   __asm_flush_cache_user_range(start,end)
> >   *
> >   *   Ensure that the I and D caches are coherent within specified region.
> >   *   This is typically used when code has been written to a memory region,
> > @@ -37,8 +37,7 @@ ENTRY(__flush_icache_range)
> >   *   - start   - virtual start address of region
> >   *   - end     - virtual end address of region
> >   */
> > -ENTRY(__flush_cache_user_range)
> > -     uaccess_ttbr0_enable x2, x3, x4
> > +ENTRY(__asm_flush_cache_user_range)
> >  alternative_if ARM64_HAS_CACHE_IDC
>
> It's unfortunate that we pulled the IDC alternative out for
> invalidate_icache_range(), but not here.

Good point. I will fix that in a separate patch.

Thank you,
Pasha