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Date: Mon, 9 Jul 2012 14:25:23 +0200
From: Michal Hocko <mhocko@suse.cz>
To: Will Deacon <will.deacon@arm.com>
Cc: linux-mm@kvack.org, akpm@linux-foundation.org, dhillf@gmail.com,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: hugetlb: flush dcache before returning zeroed huge
 page to userspace
Message-ID: <20120709122523.GC4627@tiehlicka.suse.cz>
References: <1341412376-6272-1-git-send-email-will.deacon@arm.com>
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On Wed 04-07-12 15:32:56, Will Deacon wrote:
> When allocating and returning clear huge pages to userspace as a
> response to a fault, we may zero and return a mapping to a previously
> dirtied physical region (for example, it may have been written by
> a private mapping which was freed as a result of an ftruncate on the
> backing file). On architectures with Harvard caches, this can lead to
> I/D inconsistency since the zeroed view may not be visible to the
> instruction stream.
> 
> This patch solves the problem by flushing the region after allocating
> and clearing a new huge page. Note that PowerPC avoids this issue by
> performing the flushing in their clear_user_page implementation to keep
> the loader happy, however this is closely tied to the semantics of the
> PG_arch_1 page flag which is architecture-specific.
> 
> Acked-by: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Will Deacon <will.deacon@arm.com>
> ---
>  mm/hugetlb.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index e198831..b83d026 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2646,6 +2646,7 @@ retry:
>  			goto out;
>  		}
>  		clear_huge_page(page, address, pages_per_huge_page(h));
> +		flush_dcache_page(page);
>  		__SetPageUptodate(page);

Does this have to be explicit in the arch independent code?
It seems that ia64 uses flush_dcache_page already in the clear_user_page

>  
>  		if (vma->vm_flags & VM_MAYSHARE) {
> -- 
> 1.7.4.1
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

From mboxrd@z Thu Jan  1 00:00:00 1970
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Date: Mon, 9 Jul 2012 14:25:23 +0200
From: Michal Hocko <mhocko@suse.cz>
Subject: Re: [PATCH] mm: hugetlb: flush dcache before returning zeroed huge
 page to userspace
Message-ID: <20120709122523.GC4627@tiehlicka.suse.cz>
References: <1341412376-6272-1-git-send-email-will.deacon@arm.com>
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List-ID: <linux-mm.kvack.org>
To: Will Deacon <will.deacon@arm.com>
Cc: linux-mm@kvack.org, akpm@linux-foundation.org, dhillf@gmail.com, linux-kernel@vger.kernel.org

On Wed 04-07-12 15:32:56, Will Deacon wrote:
> When allocating and returning clear huge pages to userspace as a
> response to a fault, we may zero and return a mapping to a previously
> dirtied physical region (for example, it may have been written by
> a private mapping which was freed as a result of an ftruncate on the
> backing file). On architectures with Harvard caches, this can lead to
> I/D inconsistency since the zeroed view may not be visible to the
> instruction stream.
> 
> This patch solves the problem by flushing the region after allocating
> and clearing a new huge page. Note that PowerPC avoids this issue by
> performing the flushing in their clear_user_page implementation to keep
> the loader happy, however this is closely tied to the semantics of the
> PG_arch_1 page flag which is architecture-specific.
> 
> Acked-by: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Will Deacon <will.deacon@arm.com>
> ---
>  mm/hugetlb.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index e198831..b83d026 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2646,6 +2646,7 @@ retry:
>  			goto out;
>  		}
>  		clear_huge_page(page, address, pages_per_huge_page(h));
> +		flush_dcache_page(page);
>  		__SetPageUptodate(page);

Does this have to be explicit in the arch independent code?
It seems that ia64 uses flush_dcache_page already in the clear_user_page

>  
>  		if (vma->vm_flags & VM_MAYSHARE) {
> -- 
> 1.7.4.1
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>