Subject: [PATCH 7/8] arm64: use 'physmem' memblock to improve CONFIG_STRICT_DEVMEM handling

From: [email-masked] (Will Deacon)
Date: Fri, 9 Jan 2015 15:38:17 +0000

On Mon, Dec 22, 2014 at 07:08:41PM +0000, Ard Biesheuvel wrote:
> The 'physmem' memblock table allows us to classify memory as RAM even
> if it is not covered by the ordinary 'memory' memblock table.
> 
> Under CONFIG_STRICT_DEVMEM, we can use this to:
> - allow read-only access to parts of RAM that are not considered memory
>   by the kernel, this is mainly intended for exposing UEFI configuration
>   tables such as SMBIOS to userland;
> - avoid using non-cached mappings for those parts of RAM, as it may
>   result in mismatched attributes.

Looks fine to me assuming that the rest of the series is ok:

  Acked-by: Will Deacon <[email-masked]>

Will

> Signed-off-by: Ard Biesheuvel <[email-masked]>
> ---
>  arch/arm64/Kconfig   |  1 +
>  arch/arm64/mm/mmap.c |  2 +-
>  arch/arm64/mm/mmu.c  | 15 ++++++++++++++-
>  3 files changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index b1f9a20a3677..86902f8d8e36 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -60,6 +60,7 @@ config ARM64
>  	select HAVE_GENERIC_DMA_COHERENT
>  	select HAVE_HW_BREAKPOINT if PERF_EVENTS
>  	select HAVE_MEMBLOCK
> +	select HAVE_MEMBLOCK_PHYS_MAP
>  	select HAVE_PATA_PLATFORM
>  	select HAVE_PERF_EVENTS
>  	select HAVE_PERF_REGS
> diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
> index 54922d1275b8..9f558ab41f39 100644
> --- a/arch/arm64/mm/mmap.c
> +++ b/arch/arm64/mm/mmap.c
> @@ -126,7 +126,7 @@ int devmem_is_allowed(unsigned long pfn)
>  {
>  	if (iomem_is_exclusive(pfn << PAGE_SHIFT))
>  		return 0;
> -	if (!page_is_ram(pfn))
> +	if (!pfn_valid(pfn))
>  		return 1;
>  	return 0;
>  }
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 328638548871..083be3de1a87 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -122,7 +122,7 @@ early_param("cachepolicy", early_cachepolicy);
>  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_physmem(PFN_PHYS(pfn)))
>  		return pgprot_noncached(vma_prot);
>  	else if (file->f_flags & O_SYNC)
>  		return pgprot_writecombine(vma_prot);
> @@ -130,6 +130,19 @@ pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
>  }
>  EXPORT_SYMBOL(phys_mem_access_prot);
>  
> +/*
> + * This definition of phys_mem_access_prot_allowed() overrides
> + * the __weak definition in drivers/char/mem.c
> + */
> +int phys_mem_access_prot_allowed(struct file *file, unsigned long pfn,
> +				 unsigned long size, pgprot_t *prot)
> +{
> +	/* Disallow read-write access to system RAM */
> +	if (memblock_is_physmem(PFN_PHYS(pfn)) && pgprot_val(*prot) & PTE_WRITE)
> +		return 0;
> +	return 1;
> +}
> +
>  static void __init *early_alloc(unsigned long sz)
>  {
>  	void *ptr = __va(memblock_alloc(sz, sz));
> -- 
> 1.8.3.2
> 
>