Re: [RFC V1 09/31] arm/mm: Enable ARCH_HAS_VM_GET_PAGE_PROT

["Russell King (Oracle)" <linux@armlinux.org.uk>]

On Mon, Jan 24, 2022 at 06:26:46PM +0530, Anshuman Khandual wrote:
> This defines and exports a platform specific custom vm_get_page_prot() via
> subscribing ARCH_HAS_VM_GET_PAGE_PROT. Subsequently all __SXXX and __PXXX
> macros can be dropped which are no longer needed.

What is the fundamental advantage of this approach?

> 
> Cc: Russell King <linux@armlinux.org.uk>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
>  arch/arm/Kconfig               |  1 +
>  arch/arm/include/asm/pgtable.h | 18 ------------
>  arch/arm/mm/mmu.c              | 50 ++++++++++++++++++++++++++++++----
>  3 files changed, 45 insertions(+), 24 deletions(-)
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index fabe39169b12..c12362d20c44 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -23,6 +23,7 @@ config ARM
>  	select ARCH_HAS_SYNC_DMA_FOR_CPU if SWIOTLB || !MMU
>  	select ARCH_HAS_TEARDOWN_DMA_OPS if MMU
>  	select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
> +	select ARCH_HAS_VM_GET_PAGE_PROT
>  	select ARCH_HAVE_CUSTOM_GPIO_H
>  	select ARCH_HAVE_NMI_SAFE_CMPXCHG if CPU_V7 || CPU_V7M || CPU_V6K
>  	select ARCH_HAS_GCOV_PROFILE_ALL
> diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
> index cd1f84bb40ae..ec062dd6082a 100644
> --- a/arch/arm/include/asm/pgtable.h
> +++ b/arch/arm/include/asm/pgtable.h
> @@ -137,24 +137,6 @@ extern pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
>   *  2) If we could do execute protection, then read is implied
>   *  3) write implies read permissions
>   */
> -#define __P000  __PAGE_NONE
> -#define __P001  __PAGE_READONLY
> -#define __P010  __PAGE_COPY
> -#define __P011  __PAGE_COPY
> -#define __P100  __PAGE_READONLY_EXEC
> -#define __P101  __PAGE_READONLY_EXEC
> -#define __P110  __PAGE_COPY_EXEC
> -#define __P111  __PAGE_COPY_EXEC
> -
> -#define __S000  __PAGE_NONE
> -#define __S001  __PAGE_READONLY
> -#define __S010  __PAGE_SHARED
> -#define __S011  __PAGE_SHARED
> -#define __S100  __PAGE_READONLY_EXEC
> -#define __S101  __PAGE_READONLY_EXEC
> -#define __S110  __PAGE_SHARED_EXEC
> -#define __S111  __PAGE_SHARED_EXEC
> -
>  #ifndef __ASSEMBLY__
>  /*
>   * ZERO_PAGE is a global shared page that is always zero: used
> diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
> index 274e4f73fd33..3007d07bc0e7 100644
> --- a/arch/arm/mm/mmu.c
> +++ b/arch/arm/mm/mmu.c
> @@ -403,6 +403,8 @@ void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot)
>  	local_flush_tlb_kernel_range(vaddr, vaddr + PAGE_SIZE);
>  }
>  
> +static pteval_t user_pgprot;
> +
>  /*
>   * Adjust the PMD section entries according to the CPU in use.
>   */
> @@ -410,7 +412,7 @@ static void __init build_mem_type_table(void)
>  {
>  	struct cachepolicy *cp;
>  	unsigned int cr = get_cr();
> -	pteval_t user_pgprot, kern_pgprot, vecs_pgprot;
> +	pteval_t kern_pgprot, vecs_pgprot;
>  	int cpu_arch = cpu_architecture();
>  	int i;
>  
> @@ -627,11 +629,6 @@ static void __init build_mem_type_table(void)
>  	user_pgprot |= PTE_EXT_PXN;
>  #endif
>  
> -	for (i = 0; i < 16; i++) {
> -		pteval_t v = pgprot_val(protection_map[i]);
> -		protection_map[i] = __pgprot(v | user_pgprot);
> -	}
> -
>  	mem_types[MT_LOW_VECTORS].prot_pte |= vecs_pgprot;
>  	mem_types[MT_HIGH_VECTORS].prot_pte |= vecs_pgprot;
>  
> @@ -670,6 +667,47 @@ static void __init build_mem_type_table(void)
>  	}
>  }
>  
> +pgprot_t vm_get_page_prot(unsigned long vm_flags)
> +{
> +	switch (vm_flags & (VM_READ | VM_WRITE | VM_EXEC | VM_SHARED)) {
> +	case VM_NONE:
> +		return __pgprot(pgprot_val(__PAGE_NONE) | user_pgprot);
> +	case VM_READ:
> +		return __pgprot(pgprot_val(__PAGE_READONLY) | user_pgprot);
> +	case VM_WRITE:
> +		return __pgprot(pgprot_val(__PAGE_COPY) | user_pgprot);
> +	case VM_READ | VM_WRITE:
> +		return __pgprot(pgprot_val(__PAGE_COPY) | user_pgprot);
> +	case VM_EXEC:
> +		return __pgprot(pgprot_val(__PAGE_READONLY_EXEC) | user_pgprot);
> +	case VM_EXEC | VM_READ:
> +		return __pgprot(pgprot_val(__PAGE_READONLY_EXEC) | user_pgprot);
> +	case VM_EXEC | VM_WRITE:
> +		return __pgprot(pgprot_val(__PAGE_COPY_EXEC) | user_pgprot);
> +	case VM_EXEC | VM_READ | VM_WRITE:
> +		return __pgprot(pgprot_val(__PAGE_COPY_EXEC) | user_pgprot);
> +	case VM_SHARED:
> +		return __pgprot(pgprot_val(__PAGE_NONE) | user_pgprot);
> +	case VM_SHARED | VM_READ:
> +		return __pgprot(pgprot_val(__PAGE_READONLY) | user_pgprot);
> +	case VM_SHARED | VM_WRITE:
> +		return __pgprot(pgprot_val(__PAGE_SHARED) | user_pgprot);
> +	case VM_SHARED | VM_READ | VM_WRITE:
> +		return __pgprot(pgprot_val(__PAGE_SHARED) | user_pgprot);
> +	case VM_SHARED | VM_EXEC:
> +		return __pgprot(pgprot_val(__PAGE_READONLY_EXEC) | user_pgprot);
> +	case VM_SHARED | VM_EXEC | VM_READ:
> +		return __pgprot(pgprot_val(__PAGE_READONLY_EXEC) | user_pgprot);
> +	case VM_SHARED | VM_EXEC | VM_WRITE:
> +		return __pgprot(pgprot_val(__PAGE_SHARED_EXEC) | user_pgprot);
> +	case VM_SHARED | VM_EXEC | VM_READ | VM_WRITE:
> +		return __pgprot(pgprot_val(__PAGE_SHARED_EXEC) | user_pgprot);
> +	default:
> +		BUILD_BUG();
> +	}
> +}
> +EXPORT_SYMBOL(vm_get_page_prot);
> +
>  #ifdef CONFIG_ARM_DMA_MEM_BUFFERABLE
>  pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
>  			      unsigned long size, pgprot_t vma_prot)
> -- 
> 2.25.1
> 
> 

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