linux-kernel - Re: [RFC V1 21/31] parisc/mm: Enable ARCH_HAS_VM_GET_PAGE

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Date:   Tue, 25 Jan 2022 17:53:27 +0100
From:   Rolf Eike Beer <eike-kernel@...tec.de>
To:     linux-mm@...ck.org, Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-kernel@...r.kernel.org, hch@...radead.org,
        akpm@...ux-foundation.org,
        Anshuman Khandual <anshuman.khandual@....com>,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        linux-parisc@...r.kernel.org
Subject: Re: [RFC V1 21/31] parisc/mm: Enable ARCH_HAS_VM_GET_PAGE_PROT

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.
> 
> Cc: "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>
> Cc: linux-parisc@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
>  arch/parisc/Kconfig               |  1 +
>  arch/parisc/include/asm/pgtable.h | 20 ---------------
>  arch/parisc/mm/init.c             | 41 +++++++++++++++++++++++++++++++
>  3 files changed, 42 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig
> index 43c1c880def6..de512f120b50 100644
> --- a/arch/parisc/Kconfig
> +++ b/arch/parisc/Kconfig
> @@ -10,6 +10,7 @@ config PARISC
>  	select ARCH_HAS_ELF_RANDOMIZE
>  	select ARCH_HAS_STRICT_KERNEL_RWX
>  	select ARCH_HAS_UBSAN_SANITIZE_ALL
> +	select ARCH_HAS_VM_GET_PAGE_PROT
>  	select ARCH_NO_SG_CHAIN
>  	select ARCH_SUPPORTS_HUGETLBFS if PA20
>  	select ARCH_SUPPORTS_MEMORY_FAILURE
> diff --git a/arch/parisc/include/asm/pgtable.h
> b/arch/parisc/include/asm/pgtable.h index 3e7cf882639f..80d99b2b5913 100644
> --- a/arch/parisc/include/asm/pgtable.h
> +++ b/arch/parisc/include/asm/pgtable.h
> @@ -269,26 +269,6 @@ extern void __update_cache(pte_t pte);
>   * pages.
>   */
> 
> -	 /*xwr*/
> -#define __P000  PAGE_NONE
> -#define __P001  PAGE_READONLY
> -#define __P010  __P000 /* copy on write */
> -#define __P011  __P001 /* copy on write */
> -#define __P100  PAGE_EXECREAD
> -#define __P101  PAGE_EXECREAD
> -#define __P110  __P100 /* copy on write */
> -#define __P111  __P101 /* copy on write */
> -
> -#define __S000  PAGE_NONE
> -#define __S001  PAGE_READONLY
> -#define __S010  PAGE_WRITEONLY
> -#define __S011  PAGE_SHARED
> -#define __S100  PAGE_EXECREAD
> -#define __S101  PAGE_EXECREAD
> -#define __S110  PAGE_RWX
> -#define __S111  PAGE_RWX
> -
> -
>  extern pgd_t swapper_pg_dir[]; /* declared in init_task.c */
> 
>  /* initial page tables for 0-8MB for kernel */
> diff --git a/arch/parisc/mm/init.c b/arch/parisc/mm/init.c
> index 1ae31db9988f..c8316e97e1a2 100644
> --- a/arch/parisc/mm/init.c
> +++ b/arch/parisc/mm/init.c
> @@ -866,3 +866,44 @@ void flush_tlb_all(void)
>  	spin_unlock(&sid_lock);
>  }
>  #endif
> +
> +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 PAGE_NONE;
> +	case VM_READ:
> +		return PAGE_READONLY;
> +	case VM_WRITE:
> +		return PAGE_NONE;
> +	case VM_READ | VM_WRITE:
> +		return PAGE_READONLY;

This looks extremely strange. It probably is correct when it comes to CoW, how 
about including the comment that was in the original definitions for the cases 
where CoW is expected?

> +	case VM_EXEC:
> +		return PAGE_EXECREAD;
> +	case VM_EXEC | VM_READ:
> +		return PAGE_EXECREAD;
> +	case VM_EXEC | VM_WRITE:
> +		return PAGE_EXECREAD;
> +	case VM_EXEC | VM_READ | VM_WRITE:
> +		return PAGE_EXECREAD;
> +	case VM_SHARED:
> +		return PAGE_NONE;
> +	case VM_SHARED | VM_READ:
> +		return PAGE_READONLY;
> +	case VM_SHARED | VM_WRITE:
> +		return PAGE_WRITEONLY;
> +	case VM_SHARED | VM_READ | VM_WRITE:
> +		return PAGE_SHARED;
> +	case VM_SHARED | VM_EXEC:
> +		return PAGE_EXECREAD;
> +	case VM_SHARED | VM_EXEC | VM_READ:
> +		return PAGE_EXECREAD;
> +	case VM_SHARED | VM_EXEC | VM_WRITE:
> +		return PAGE_RWX;
> +	case VM_SHARED | VM_EXEC | VM_READ | VM_WRITE:
> +		return PAGE_RWX;
> +	default:
> +		BUILD_BUG();
> +	}
> +}
> +EXPORT_SYMBOL(vm_get_page_prot);


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