linux-kernel - Re: [PATCH] arm: Extend the check for RAM in /dev/mem

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Message-ID: <1562944417.1345.17.camel@amazon.de>
Date:   Fri, 12 Jul 2019 15:13:38 +0000
From:   "Raslan, KarimAllah" <karahmed@...zon.de>
To:     "will@...nel.org" <will@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
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Subject: Re: [PATCH] arm: Extend the check for RAM in /dev/mem

On Fri, 2019-07-12 at 15:57 +0100, Will Deacon wrote:
> On Fri, Jul 12, 2019 at 12:21:21AM +0200, KarimAllah Ahmed wrote:
> > 
> > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> > index 3645f29..cdc3e8e 100644
> > --- a/arch/arm64/mm/mmu.c
> > +++ b/arch/arm64/mm/mmu.c
> > @@ -78,7 +78,7 @@ void set_swapper_pgd(pgd_t *pgdp, pgd_t pgd)
> >  pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
> >  			      unsigned long size, pgprot_t vma_prot)
> >  {
> > -	if (!pfn_valid(pfn))
> > +	if (!memblock_is_memory(__pfn_to_phys(pfn)))
> 
> This looks broken to me, since it will end up returning 'true' for nomap
> memory and we really don't want to map that using writeback attributes.

True, I will fix this by using memblock_is_map_memory instead. That said, do
you have any concerns about this approach in general?

> 
> Will



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