linux-kernel - Re: [PATCH v2 09/17] powerpc/mm: Add new hash_page

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Date:	Wed, 01 Oct 2014 15:13:05 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Michael Neuling <mikey@...ling.org>, greg@...ah.com, arnd@...db.de,
	mpe@...erman.id.au, benh@...nel.crashing.org
Cc:	mikey@...ling.org, anton@...ba.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...abs.org, jk@...abs.org, imunsie@....ibm.com,
	cbe-oss-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2 09/17] powerpc/mm: Add new hash_page_mm()

Michael Neuling <mikey@...ling.org> writes:

> From: Ian Munsie <imunsie@....ibm.com>
>
> This adds a new function hash_page_mm() based on the existing hash_page().
> This version allows any struct mm to be passed in, rather than assuming
> current.  This is useful for servicing co-processor faults which are not in the
> context of the current running process.
>
> We need to be careful here as the current hash_page() assumes current in a few
> places.

It would be nice to document the rules here. So when we try to add a hash
page entry, and if that result in demotion of the segment are we suppose to
flush slbs ? Also why would one want to hash anything other
than current->mm ? How will this get called ? 

May be they are explained in later patches. But can we also explain it
here. 

>
> Signed-off-by: Ian Munsie <imunsie@....ibm.com>
> Signed-off-by: Michael Neuling <mikey@...ling.org>
> ---
>  arch/powerpc/include/asm/mmu-hash64.h |  1 +
>  arch/powerpc/mm/hash_utils_64.c       | 22 ++++++++++++++--------
>  2 files changed, 15 insertions(+), 8 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/mmu-hash64.h b/arch/powerpc/include/asm/mmu-hash64.h
> index 6d0b7a2..f84e5a5 100644
> --- a/arch/powerpc/include/asm/mmu-hash64.h
> +++ b/arch/powerpc/include/asm/mmu-hash64.h
> @@ -322,6 +322,7 @@ extern int __hash_page_64K(unsigned long ea, unsigned long access,
>  			   unsigned int local, int ssize);
>  struct mm_struct;
>  unsigned int hash_page_do_lazy_icache(unsigned int pp, pte_t pte, int trap);
> +extern int hash_page_mm(struct mm_struct *mm, unsigned long ea, unsigned long access, unsigned long trap);
>  extern int hash_page(unsigned long ea, unsigned long access, unsigned long trap);
>  int __hash_page_huge(unsigned long ea, unsigned long access, unsigned long vsid,
>  		     pte_t *ptep, unsigned long trap, int local, int ssize,
> diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
> index bbdb054..0a5c8c0 100644
> --- a/arch/powerpc/mm/hash_utils_64.c
> +++ b/arch/powerpc/mm/hash_utils_64.c
> @@ -904,7 +904,7 @@ void demote_segment_4k(struct mm_struct *mm, unsigned long addr)
>  		return;
>  	slice_set_range_psize(mm, addr, 1, MMU_PAGE_4K);
>  	copro_flush_all_slbs(mm);
> -	if (get_paca_psize(addr) != MMU_PAGE_4K) {
> +	if ((get_paca_psize(addr) != MMU_PAGE_4K) && (current->mm == mm)) {
>  		get_paca()->context = mm->context;
>  		slb_flush_and_rebolt();
>  	}
> @@ -989,26 +989,24 @@ static void check_paca_psize(unsigned long ea, struct mm_struct *mm,
>   * -1 - critical hash insertion error
>   * -2 - access not permitted by subpage protection mechanism
>   */
> -int hash_page(unsigned long ea, unsigned long access, unsigned long trap)
> +int hash_page_mm(struct mm_struct *mm, unsigned long ea, unsigned long access, unsigned long trap)
>  {
>  	enum ctx_state prev_state = exception_enter();
>  	pgd_t *pgdir;
>  	unsigned long vsid;
> -	struct mm_struct *mm;
>  	pte_t *ptep;
>  	unsigned hugeshift;
>  	const struct cpumask *tmp;
>  	int rc, user_region = 0, local = 0;
>  	int psize, ssize;
>  
> -	DBG_LOW("hash_page(ea=%016lx, access=%lx, trap=%lx\n",
> -		ea, access, trap);
> +	DBG_LOW("%s(ea=%016lx, access=%lx, trap=%lx\n",
> +		__func__, ea, access, trap);
>  
>  	/* Get region & vsid */
>   	switch (REGION_ID(ea)) {
>  	case USER_REGION_ID:
>  		user_region = 1;
> -		mm = current->mm;
>  		if (! mm) {
>  			DBG_LOW(" user region with no mm !\n");
>  			rc = 1;
> @@ -1104,7 +1102,8 @@ int hash_page(unsigned long ea, unsigned long access, unsigned long trap)
>  			WARN_ON(1);
>  		}
>  #endif
> -		check_paca_psize(ea, mm, psize, user_region);
> +		if (current->mm == mm)
> +			check_paca_psize(ea, mm, psize, user_region);
>  
>  		goto bail;
>  	}
> @@ -1145,7 +1144,8 @@ int hash_page(unsigned long ea, unsigned long access, unsigned long trap)
>  		}
>  	}
>  
> -	check_paca_psize(ea, mm, psize, user_region);
> +	if (current->mm == mm)
> +		check_paca_psize(ea, mm, psize, user_region);
>  #endif /* CONFIG_PPC_64K_PAGES */
>  
>  #ifdef CONFIG_PPC_HAS_HASH_64K
> @@ -1180,6 +1180,12 @@ bail:
>  	exception_exit(prev_state);
>  	return rc;
>  }
> +EXPORT_SYMBOL_GPL(hash_page_mm);
> +
> +int hash_page(unsigned long ea, unsigned long access, unsigned long trap)
> +{
> +	return hash_page_mm(current->mm, ea, access, trap);
> +}
>  EXPORT_SYMBOL_GPL(hash_page);
>  
>  void hash_preload(struct mm_struct *mm, unsigned long ea,
> -- 
> 1.9.1
>
> --
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