linux-kernel - Re: [PATCH V2 1/2] mm/autonuma: Let architecture override how the write bit should be stashed in a protnone pte.

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Message-Id: <87poilmien.fsf@concordia.ellerman.id.au>
Date:   Tue, 14 Feb 2017 16:49:04 +1100
From:   Michael Ellerman <michaele@....ibm.com>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        akpm@...ux-foundation.org, Rik van Riel <riel@...riel.com>,
        Mel Gorman <mgorman@...hsingularity.net>, paulus@...abs.org,
        benh@...nel.crashing.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: Re: [PATCH V2 1/2] mm/autonuma: Let architecture override how the write bit should be stashed in a protnone pte.

"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> writes:

> Autonuma preserves the write permission across numa fault to avoid taking
> a writefault after a numa fault (Commit: b191f9b106ea " mm: numa: preserve PTE
> write permissions across a NUMA hinting fault"). Architecture can implement
> protnone in different ways and some may choose to implement that by clearing Read/
> Write/Exec bit of pte. Setting the write bit on such pte can result in wrong
> behaviour. Fix this up by allowing arch to override how to save the write bit
> on a protnone pte.

This is pretty obviously a nop on arches that don't implement the new
hooks, but it'd still be good to get an ack from someone in mm land
before I merge it.

cheers

> Acked-By: Michael Neuling <mikey@...ling.org>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> ---
>  include/asm-generic/pgtable.h | 16 ++++++++++++++++
>  mm/huge_memory.c              |  4 ++--
>  mm/memory.c                   |  2 +-
>  mm/mprotect.c                 |  4 ++--
>  4 files changed, 21 insertions(+), 5 deletions(-)
>
> diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
> index 18af2bcefe6a..b6f3a8a4b738 100644
> --- a/include/asm-generic/pgtable.h
> +++ b/include/asm-generic/pgtable.h
> @@ -192,6 +192,22 @@ static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addres
>  }
>  #endif
>  
> +#ifndef pte_savedwrite
> +#define pte_savedwrite pte_write
> +#endif
> +
> +#ifndef pte_mk_savedwrite
> +#define pte_mk_savedwrite pte_mkwrite
> +#endif
> +
> +#ifndef pmd_savedwrite
> +#define pmd_savedwrite pmd_write
> +#endif
> +
> +#ifndef pmd_mk_savedwrite
> +#define pmd_mk_savedwrite pmd_mkwrite
> +#endif
> +
>  #ifndef __HAVE_ARCH_PMDP_SET_WRPROTECT
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>  static inline void pmdp_set_wrprotect(struct mm_struct *mm,
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 9a6bd6c8d55a..2f0f855ec911 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1300,7 +1300,7 @@ int do_huge_pmd_numa_page(struct vm_fault *vmf, pmd_t pmd)
>  	goto out;
>  clear_pmdnuma:
>  	BUG_ON(!PageLocked(page));
> -	was_writable = pmd_write(pmd);
> +	was_writable = pmd_savedwrite(pmd);
>  	pmd = pmd_modify(pmd, vma->vm_page_prot);
>  	pmd = pmd_mkyoung(pmd);
>  	if (was_writable)
> @@ -1555,7 +1555,7 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
>  			entry = pmdp_huge_get_and_clear_notify(mm, addr, pmd);
>  			entry = pmd_modify(entry, newprot);
>  			if (preserve_write)
> -				entry = pmd_mkwrite(entry);
> +				entry = pmd_mk_savedwrite(entry);
>  			ret = HPAGE_PMD_NR;
>  			set_pmd_at(mm, addr, pmd, entry);
>  			BUG_ON(vma_is_anonymous(vma) && !preserve_write &&
> diff --git a/mm/memory.c b/mm/memory.c
> index e78bf72f30dd..88c24f89d6d3 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3388,7 +3388,7 @@ static int do_numa_page(struct vm_fault *vmf)
>  	int target_nid;
>  	bool migrated = false;
>  	pte_t pte;
> -	bool was_writable = pte_write(vmf->orig_pte);
> +	bool was_writable = pte_savedwrite(vmf->orig_pte);
>  	int flags = 0;
>  
>  	/*
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index f9c07f54dd62..15f5c174a7c1 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -113,13 +113,13 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
>  			ptent = ptep_modify_prot_start(mm, addr, pte);
>  			ptent = pte_modify(ptent, newprot);
>  			if (preserve_write)
> -				ptent = pte_mkwrite(ptent);
> +				ptent = pte_mk_savedwrite(ptent);
>  
>  			/* Avoid taking write faults for known dirty pages */
>  			if (dirty_accountable && pte_dirty(ptent) &&
>  					(pte_soft_dirty(ptent) ||
>  					 !(vma->vm_flags & VM_SOFTDIRTY))) {
> -				ptent = pte_mkwrite(ptent);
> +				ptent = pte_mk_savedwrite(ptent);
>  			}
>  			ptep_modify_prot_commit(mm, addr, pte, ptent);
>  			pages++;
> -- 
> 2.7.4