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Message-ID: <Ye7cs4fNMGPZIV2U@shell.armlinux.org.uk>
Date: Mon, 24 Jan 2022 17:06:59 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Anshuman Khandual <anshuman.khandual@....com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
hch@...radead.org, akpm@...ux-foundation.org,
Arnd Bergmann <arnd@...db.de>,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC V1 09/31] arm/mm: Enable ARCH_HAS_VM_GET_PAGE_PROT
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@...linux.org.uk>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....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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