linux-kernel - Re: [PATCH V2 08/11] arch/kmap: Ensure kmap

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Date:   Wed, 6 May 2020 13:33:39 -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>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        Dan Williams <dan.j.williams@...el.com>,
        linux-snps-arc@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-csky@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-parisc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, sparclinux@...r.kernel.org,
        linux-xtensa@...ux-xtensa.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH V2 08/11] arch/kmap: Ensure kmap_prot visibility

On Tue, May 05, 2020 at 11:13:26PM -0700, Christoph Hellwig wrote:
> On Sun, May 03, 2020 at 06:09:09PM -0700, ira.weiny@...el.com wrote:
> > From: Ira Weiny <ira.weiny@...el.com>
> > 
> > We want to support kmap_atomic_prot() on all architectures and it makes
> > sense to define kmap_atomic() to use the default kmap_prot.
> > 
> > So we ensure all arch's have a globally available kmap_prot either as a
> > define or exported symbol.
> 
> FYI, I still think a
> 
> #ifndef kmap_prot
> #define kmap_prot PAGE_KERNEL
> #endif
> 
> in linux/highmem.h would be nicer.  Then only xtensa and sparc need
> to override it and clearly stand out.

That would be nice...  But...  in this particular patch kmap_prot needs to be
in arch/microblaze/include/asm/highmem.h to preserve bisect-ability.

So there would be an inversion with this define and the core #ifndef...

I like the change but I'm going to add this change as a follow on patch because
at the end of the series microblaze no longer needs this.

If this is reasonable could I get a review on this patch to add to the next
series?

Ira