Re: [PATCH 2/6] arm64/mm: add create_pgd_mapping() to create private page tables

[Steve Capper <steve.capper-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>]

On Fri, Oct 24, 2014 at 02:39:40PM +0200, Ard Biesheuvel wrote:
> For UEFI, we need to install the memory mappings used for Runtime Services
> in a dedicated set of page tables. Add create_pgd_mapping(), which allows
> us to allocate and install those page table entries early.
> This also adds a 'map_xn' option, that creates regions with the PXN and
> UXN bits set.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>

Hi Ard,

Some comments below...

> ---
>  arch/arm64/include/asm/mmu.h |  3 +++
>  arch/arm64/mm/mmu.c          | 28 ++++++++++++++++++++--------
>  2 files changed, 23 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
> index c2f006c48bdb..bcf166043a8b 100644
> --- a/arch/arm64/include/asm/mmu.h
> +++ b/arch/arm64/include/asm/mmu.h
> @@ -33,5 +33,8 @@ extern void __iomem *early_io_map(phys_addr_t phys, unsigned long virt);
>  extern void init_mem_pgprot(void);
>  /* create an identity mapping for memory (or io if map_io is true) */
>  extern void create_id_mapping(phys_addr_t addr, phys_addr_t size, int map_io);
> +extern void create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
> +			       unsigned long virt, phys_addr_t size,
> +			       int map_io, int map_xn);

I really don't like these map_io and map_xn parameters.
Further down we have logic "if (map_io)...", which is out of place, and
doesn't match the normal style of mapping page table entries.

Could we not instead have something like:
extern void create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
			       unsigned long virt, phys_addr_t size,
			       pgprot_t prot_sect, pgprot_t prot_pte);

Then we can remove all the conditional logic for map_io, map_xn?

>  
>  #endif
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 7eaa6a8c8467..f7d17a5a1f56 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -157,7 +157,7 @@ static void __init alloc_init_pte(pmd_t *pmd, unsigned long addr,
>  
>  static void __init alloc_init_pmd(struct mm_struct *mm, pud_t *pud,
>  				  unsigned long addr, unsigned long end,
> -				  phys_addr_t phys, int map_io)
> +				  phys_addr_t phys, int map_io, int map_xn)
>  {
>  	pmd_t *pmd;
>  	unsigned long next;
> @@ -167,6 +167,9 @@ static void __init alloc_init_pmd(struct mm_struct *mm, pud_t *pud,
>  	if (map_io) {
>  		prot_sect = PROT_SECT_DEVICE_nGnRE;
>  		prot_pte = __pgprot(PROT_DEVICE_nGnRE);
> +	} else if (map_xn) {
> +		prot_sect = PROT_SECT_NORMAL;
> +		prot_pte = PAGE_KERNEL;
>  	} else {
>  		prot_sect = PROT_SECT_NORMAL_EXEC;
>  		prot_pte = PAGE_KERNEL_EXEC;

Ideally, this if block should be completely removed.

> @@ -203,7 +206,7 @@ static void __init alloc_init_pmd(struct mm_struct *mm, pud_t *pud,
>  
>  static void __init alloc_init_pud(struct mm_struct *mm, pgd_t *pgd,
>  				  unsigned long addr, unsigned long end,
> -				  unsigned long phys, int map_io)
> +				  unsigned long phys, int map_io, int map_xn)
>  {
>  	pud_t *pud;
>  	unsigned long next;
> @@ -221,7 +224,7 @@ static void __init alloc_init_pud(struct mm_struct *mm, pgd_t *pgd,
>  		/*
>  		 * For 4K granule only, attempt to put down a 1GB block
>  		 */
> -		if (!map_io && (PAGE_SHIFT == 12) &&
> +		if (!map_io && !map_xn && (PAGE_SHIFT == 12) &&

Presumably the !map_io and !map_xn tests are here because of the
PROT_SECT_NORMAL_EXEC below? Is there another reason why a pud mapping
would be unsuitable for these?

>  		    ((addr | next | phys) & ~PUD_MASK) == 0) {
>  			pud_t old_pud = *pud;
>  			set_pud(pud, __pud(phys | PROT_SECT_NORMAL_EXEC));
> @@ -239,7 +242,8 @@ static void __init alloc_init_pud(struct mm_struct *mm, pgd_t *pgd,
>  				flush_tlb_all();
>  			}
>  		} else {
> -			alloc_init_pmd(mm, pud, addr, next, phys, map_io);
> +			alloc_init_pmd(mm, pud, addr, next, phys, map_io,
> +				       map_xn);
>  		}
>  		phys += next - addr;
>  	} while (pud++, addr = next, addr != end);
> @@ -251,7 +255,7 @@ static void __init alloc_init_pud(struct mm_struct *mm, pgd_t *pgd,
>   */
>  static void __init __create_mapping(struct mm_struct *mm, pgd_t *pgd,
>  				    phys_addr_t phys, unsigned long virt,
> -				    phys_addr_t size, int map_io)
> +				    phys_addr_t size, int map_io, int map_xn)
>  {
>  	unsigned long addr, length, end, next;
>  
> @@ -261,7 +265,7 @@ static void __init __create_mapping(struct mm_struct *mm, pgd_t *pgd,
>  	end = addr + length;
>  	do {
>  		next = pgd_addr_end(addr, end);
> -		alloc_init_pud(mm, pgd, addr, next, phys, map_io);
> +		alloc_init_pud(mm, pgd, addr, next, phys, map_io, map_xn);
>  		phys += next - addr;
>  	} while (pgd++, addr = next, addr != end);
>  }
> @@ -275,7 +279,7 @@ static void __init create_mapping(phys_addr_t phys, unsigned long virt,
>  		return;
>  	}
>  	__create_mapping(&init_mm, pgd_offset_k(virt & PAGE_MASK), phys, virt,
> -			 size, 0);
> +			 size, 0, 0);
>  }
>  
>  void __init create_id_mapping(phys_addr_t addr, phys_addr_t size, int map_io)
> @@ -285,7 +289,15 @@ void __init create_id_mapping(phys_addr_t addr, phys_addr_t size, int map_io)
>  		return;
>  	}
>  	__create_mapping(&init_mm, &idmap_pg_dir[pgd_index(addr)],
> -			 addr, addr, size, map_io);
> +			 addr, addr, size, map_io, 0);
> +}
> +
> +void __init create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
> +			       unsigned long virt, phys_addr_t size,
> +			       int map_io, int map_xn)
> +{
> +	__create_mapping(mm, pgd_offset(mm, virt), phys, virt, size, map_io,
> +			 map_xn);
>  }
>  
>  static void __init map_mem(void)
> -- 
> 1.8.3.2
> 

Cheers,
-- 
Steve