linux-kernel - Re: [PATCH 1/5] lib: Add a generic version of devmem_is

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Message-ID: <20200710053850.GA27019@infradead.org>
Date:   Fri, 10 Jul 2020 06:38:50 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Mike Rapoport <rppt@...ux.ibm.com>
Cc:     Palmer Dabbelt <palmer@...belt.com>, mark.rutland@....com,
        steve@....org, davidgow@...gle.com, catalin.marinas@....com,
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Subject: Re: [PATCH 1/5] lib: Add a generic version of devmem_is_allowed()

On Thu, Jul 09, 2020 at 11:49:21PM +0300, Mike Rapoport wrote:
> > +#ifndef CONFIG_GENERIC_DEVMEM_IS_ALLOWED
> > +extern int devmem_is_allowed(unsigned long pfn);
> > +#endif

Nit: no need for the extern here.

> > +config GENERIC_LIB_DEVMEM_IS_ALLOWED
> > +	bool
> > +	select ARCH_HAS_DEVMEM_IS_ALLOWED
> 
> This seems to work the other way around from the usual Kconfig chains.
> In the most cases ARCH_HAS_SOMETHING selects GENERIC_SOMETHING.
> 
> I believe nicer way would be to make 
> 
> config STRICT_DEVMEM
> 	bool "Filter access to /dev/mem"
> 	depends on MMU && DEVMEM
> 	depends on ARCH_HAS_DEVMEM_IS_ALLOWED || GENERIC_LIB_DEVMEM_IS_ALLOWED
> 
> config GENERIC_LIB_DEVMEM_IS_ALLOWED
> 	bool
> 
> and then s/select ARCH_HAS_DEVMEM_IS_ALLOWED/select GENERIC_LIB_DEVMEM_IS_ALLOWED/
> in the arch Kconfigs and drop ARCH_HAS_DEVMEM_IS_ALLOWED in the end.

To take a step back:  Is there any reason to not just always
STRICT_DEVMEM? Maybe for a few architectures that don't currently
support a strict /dev/mem the generic version isn't quite correct, but
someone selecting the option and finding the issue is the best way to
figure that out..