Re: [ALTERNATE PATCH] memblock: fix min_low_pfn/max_low_pfn build errors

[Mike Rapoport]

On Fri, Aug 28, 2020 at 05:01:39PM -0700, Randy Dunlap wrote:
> Export min_low_pfn & max_low_pfn in mm/memblock.c to fix build errors
> on arch/microblaze/ and arch/ia64/: (e.g.)

Please don't. This would give driver developers a wrong impression that
these variables can be used to query memory boundaries, but this is not
the case, at least not on all architectures.

I would prefer fixing it up locally for microblaze and ia64.

>   ERROR: "max_low_pfn" [drivers/rpmsg/virtio_rpmsg_bus.ko] undefined!
>   ERROR: "min_low_pfn" [drivers/rpmsg/virtio_rpmsg_bus.ko] undefined!
>   ERROR: "max_low_pfn" [drivers/mtd/spi-nor/spi-nor.ko] undefined!
>   ERROR: "min_low_pfn" [drivers/mtd/spi-nor/spi-nor.ko] undefined!
>   ERROR: "min_low_pfn" [drivers/mtd/nand/raw/nand.ko] undefined!
>   ERROR: "max_low_pfn" [drivers/mtd/nand/raw/nand.ko] undefined!
>   ERROR: "max_low_pfn" [drivers/rapidio/devices/rio_mport_cdev.ko] undefined!
>   ERROR: "min_low_pfn" [drivers/rapidio/devices/rio_mport_cdev.ko] undefined!
>   ERROR: "min_low_pfn" [drivers/hwtracing/intel_th/intel_th_msu.ko] undefined!
>   ERROR: "max_low_pfn" [drivers/hwtracing/intel_th/intel_th_msu.ko] undefined!
>   ERROR: "min_low_pfn" [drivers/crypto/cavium/nitrox/n5pf.ko] undefined!
>   ERROR: "max_low_pfn" [drivers/crypto/cavium/nitrox/n5pf.ko] undefined!
>   ERROR: "max_low_pfn" [drivers/md/dm-integrity.ko] undefined!
>   ERROR: "min_low_pfn" [drivers/md/dm-integrity.ko] undefined!
>   ERROR: "max_low_pfn" [crypto/tcrypt.ko] undefined!
>   ERROR: "min_low_pfn" [crypto/tcrypt.ko] undefined!
> 
> In both arches, these variables are referenced in
> arch/$ARCH/include/asm/page.h.
> 
> Mike had/has an alternate patch for Microblaze:
> https://lore.kernel.org/lkml/20200630111519.GA1951986@xxxxxxxxxxxxx/
> 
> David suggested just exporting min_low_pfn & max_low_pfn in
> mm/memblock.c:
> https://lore.kernel.org/lkml/alpine.DEB.2.22.394.2006291911220.1118534@xxxxxxxxxxxxxxxxxxxxxxxxx/
> 
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Suggested-by: David Rientjes <rientjes@xxxxxxxxxx>
> Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> Cc: Michal Simek <monstr@xxxxxxxxx>
> Cc: Michal Simek <michal.simek@xxxxxxxxxx>
> Cc: Tony Luck <tony.luck@xxxxxxxxx>
> Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
> Cc: linux-ia64@xxxxxxxxxxxxxxx
> ---
>  mm/memblock.c |    2 ++
>  1 file changed, 2 insertions(+)
> 
> --- linux-next-20200825.orig/mm/memblock.c
> +++ linux-next-20200825/mm/memblock.c
> @@ -99,6 +99,8 @@ EXPORT_SYMBOL(contig_page_data);
>  
>  unsigned long max_low_pfn;
>  unsigned long min_low_pfn;
> +EXPORT_SYMBOL(min_low_pfn);
> +EXPORT_SYMBOL(max_low_pfn);
>  unsigned long max_pfn;
>  unsigned long long max_possible_pfn;
>  

-- 
Sincerely yours,
Mike.