linux-kernel - Re: sparc-related comment, to Re: [PATCH V1 07/10] arch/kmap: Ensure kmap

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Date:   Fri, 1 May 2020 08:35:52 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian Koenig <christian.koenig@....com>,
        Huang Rui <ray.huang@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        dri-devel@...ts.freedesktop.org,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        Max Filippov <jcmvbkbc@...il.com>,
        Paul Mackerras <paulus@...ba.org>,
        "H. Peter Anvin" <hpa@...or.com>, sparclinux@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Helge Deller <deller@....de>, x86@...nel.org,
        linux-csky@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        linux-snps-arc@...ts.infradead.org, linux-xtensa@...ux-xtensa.org,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        linux-arm-kernel@...ts.infradead.org,
        Chris Zankel <chris@...kel.net>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-parisc@...r.kernel.org, linux-mips@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: sparc-related comment, to Re: [PATCH V1 07/10] arch/kmap: Ensure
 kmap_prot visibility

On Fri, May 01, 2020 at 01:44:46AM -0700, Christoph Hellwig wrote:
> > --- a/arch/sparc/mm/highmem.c
> > +++ b/arch/sparc/mm/highmem.c
> > @@ -33,6 +33,7 @@
> >  #include <asm/vaddrs.h>
> >  
> >  pgprot_t kmap_prot;
> > +EXPORT_SYMBOL(kmap_prot);
> 
> Btw, I don't see why sparc needs this as a variable, as there is just
> a single assignment to it.

Because sparc uses non-standard defines which I'm not familiar with.

        kmap_prot = __pgprot(SRMMU_ET_PTE | SRMMU_PRIV | SRMMU_CACHE);

SRMMU_ET_PTE and friends are defined in 

arch/sparc/include/asm/pgtsrmmu.h

Since I can't readily test sparc this was easier to put out than let 0-day
crank on the entire series checking if including that header in the common
header chain would be an issue.

> 
> If sparc is sorted out we can always make it a define, and use a define
> for kmap_prot that defaults to PAGE_KERNEL, avoiding a little
> more duplication.

Agreed.  But it seems easier as a follow up (for me with 0-day).  Perhaps
someone from sparc can weigh in on the specifics of those defines and why they
are different from the normal ones?  Or even provide a follow on patch?

Ira