linux-kernel - Re: [PATCH] Initialise mmu_notifier

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Message-ID: <20190103143116.GB3395@redhat.com>
Date:   Thu, 3 Jan 2019 09:31:16 -0500
From:   Jerome Glisse <jglisse@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        Christian König <christian.koenig@....com>,
        Jan Kara <jack@...e.cz>
Subject: Re: [PATCH] Initialise mmu_notifier_range correctly

On Wed, Jan 02, 2019 at 04:21:26PM -0800, Matthew Wilcox wrote:
> 
> One of the paths in follow_pte_pmd() initialised the mmu_notifier_range
> incorrectly.
> 
> Signed-off-by: Matthew Wilcox <willy@...radead.org>
> Fixes: ac46d4f3c432 ("mm/mmu_notifier: use structure for invalidate_range_start/end calls v2")
> Tested-by: Dave Chinner <dchinner@...hat.com>

Actually now that i have read the code again this is not ok to
do so. The caller of follow_pte_pmd() will call range_init and
follow pmd will only update the range address. So existing code
is ok.

I know this is kind of ugly but i do not see a way around that
uglyness.

> 
> diff --git a/mm/memory.c b/mm/memory.c
> index 2dd2f9ab57f4..21a650368be0 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4078,8 +4078,8 @@ static int __follow_pte_pmd(struct mm_struct *mm, unsigned long address,
>  		goto out;
>  
>  	if (range) {
> -		range->start = address & PAGE_MASK;
> -		range->end = range->start + PAGE_SIZE;
> +		mmu_notifier_range_init(range, mm, address & PAGE_MASK,
> +				     (address & PAGE_MASK) + PAGE_SIZE);
>  		mmu_notifier_invalidate_range_start(range);
>  	}
>  	ptep = pte_offset_map_lock(mm, pmd, address, ptlp);