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

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Date:   Fri, 12 Jul 2019 15:57:12 +0100
From:   Will Deacon <will@...nel.org>
To:     KarimAllah Ahmed <karahmed@...zon.de>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Anders Roxell <anders.roxell@...aro.org>,
        Enrico Weigelt <info@...ux.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mark Rutland <mark.rutland@....com>,
        James Morse <james.morse@....com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Jun Yao <yaojun8558363@...il.com>, Yu Zhao <yuzhao@...gle.com>,
        Robin Murphy <robin.murphy@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [PATCH] arm: Extend the check for RAM in /dev/mem

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.

Will