Re: [PATCH v2 1/2] powerpc/book3s/hash: Drop _PAGE_PRIVILEGED from PAGE_NONE

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 04/12/2023 à 10:36, aneesh.kumar@kernel.org a écrit :
> From: "Aneesh Kumar K.V (IBM)" <aneesh.kumar@kernel.org>
> 
> There used to be a dependency on _PAGE_PRIVILEGED with pte_savedwrite.
> But that got dropped by
> commit 6a56ccbcf6c6 ("mm/autonuma: use can_change_(pte|pmd)_writable() to replace savedwrite")
> 
> With the change in this patch numa fault pte (pte_protnone()) gets mapped as regular user pte
> with RWX cleared (no-access) whereas earlier it used to be mapped _PAGE_PRIVILEGED.
> 
> Hash fault handling code gets some WARN_ON added in this patch because
> those functions are not expected to get called with _PAGE_READ cleared.
> commit 18061c17c8ec ("powerpc/mm: Update PROTFAULT handling in the page
> fault path") explains the details.
> 
> Signed-off-by: Aneesh Kumar K.V (IBM) <aneesh.kumar@kernel.org>

Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>

> ---
>   arch/powerpc/include/asm/book3s/64/pgtable.h | 10 ++--------
>   arch/powerpc/mm/book3s64/hash_utils.c        |  7 +++++++
>   2 files changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
> index cb77eddca54b..927d585652bc 100644
> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
> @@ -17,12 +17,6 @@
>   #define _PAGE_EXEC		0x00001 /* execute permission */
>   #define _PAGE_WRITE		0x00002 /* write access allowed */
>   #define _PAGE_READ		0x00004	/* read access allowed */
> -#define _PAGE_NA		_PAGE_PRIVILEGED
> -#define _PAGE_NAX		_PAGE_EXEC
> -#define _PAGE_RO		_PAGE_READ
> -#define _PAGE_ROX		(_PAGE_READ | _PAGE_EXEC)
> -#define _PAGE_RW		(_PAGE_READ | _PAGE_WRITE)
> -#define _PAGE_RWX		(_PAGE_READ | _PAGE_WRITE | _PAGE_EXEC)
>   #define _PAGE_PRIVILEGED	0x00008 /* kernel access only */
>   #define _PAGE_SAO		0x00010 /* Strong access order */
>   #define _PAGE_NON_IDEMPOTENT	0x00020 /* non idempotent memory */
> @@ -532,8 +526,8 @@ static inline bool pte_user(pte_t pte)
>   static inline bool pte_access_permitted(pte_t pte, bool write)
>   {
>   	/*
> -	 * _PAGE_READ is needed for any access and will be
> -	 * cleared for PROT_NONE
> +	 * _PAGE_READ is needed for any access and will be cleared for
> +	 * PROT_NONE. Execute-only mapping via PROT_EXEC also returns false.
>   	 */
>   	if (!pte_present(pte) || !pte_user(pte) || !pte_read(pte))
>   		return false;
> diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c
> index ad2afa08e62e..0626a25b0d72 100644
> --- a/arch/powerpc/mm/book3s64/hash_utils.c
> +++ b/arch/powerpc/mm/book3s64/hash_utils.c
> @@ -310,9 +310,16 @@ unsigned long htab_convert_pte_flags(unsigned long pteflags, unsigned long flags
>   			else
>   				rflags |= 0x3;
>   		}
> +		VM_WARN_ONCE(!(pteflags & _PAGE_RWX), "no-access mapping request");
>   	} else {
>   		if (pteflags & _PAGE_RWX)
>   			rflags |= 0x2;
> +		/*
> +		 * We should never hit this in normal fault handling because
> +		 * a permission check (check_pte_access()) will bubble this
> +		 * to higher level linux handler even for PAGE_NONE.
> +		 */
> +		VM_WARN_ONCE(!(pteflags & _PAGE_RWX), "no-access mapping request");
>   		if (!((pteflags & _PAGE_WRITE) && (pteflags & _PAGE_DIRTY)))
>   			rflags |= 0x1;
>   	}