linux-kernel - Re: [PATCH] mm/smaps: Don't access young/dirty bit if pte unpresent

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Message-ID: <c6ff0967-eae8-9ec1-6024-16c9b654e917@kernel.org>
Date:   Thu, 4 Aug 2022 11:02:23 +0200
From:   "Vlastimil Babka (SUSE)" <vbabka@...nel.org>
To:     Peter Xu <peterx@...hat.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Cc:     Yang Shi <shy828301@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nadav Amit <nadav.amit@...il.com>,
        David Hildenbrand <david@...hat.com>,
        Konstantin Khlebnikov <khlebnikov@...nvz.org>
Subject: Re: [PATCH] mm/smaps: Don't access young/dirty bit if pte unpresent

On 8/4/22 00:03, Peter Xu wrote:
> These bits should only be valid when the ptes are present.  Introducing two
> booleans for it and set it to false when !pte_present().
> 
> Cc: Konstantin Khlebnikov <khlebnikov@...nvz.org>
> Fixes: b1d4d9e0cbd0 ("proc/smaps: carefully handle migration entries", 2012-05-31)
> Signed-off-by: Peter Xu <peterx@...hat.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>  fs/proc/task_mmu.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 9913f3be9fd2..482f91577f8c 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -527,10 +527,12 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
>  	struct vm_area_struct *vma = walk->vma;
>  	bool locked = !!(vma->vm_flags & VM_LOCKED);
>  	struct page *page = NULL;
> -	bool migration = false;
> +	bool migration = false, young = false, dirty = false;
>  
>  	if (pte_present(*pte)) {
>  		page = vm_normal_page(vma, addr, *pte);
> +		young = pte_young(*pte);
> +		dirty = pte_dirty(*pte);
>  	} else if (is_swap_pte(*pte)) {
>  		swp_entry_t swpent = pte_to_swp_entry(*pte);
>  
> @@ -560,8 +562,7 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
>  	if (!page)
>  		return;
>  
> -	smaps_account(mss, page, false, pte_young(*pte), pte_dirty(*pte),
> -		      locked, migration);
> +	smaps_account(mss, page, false, young, dirty, locked, migration);
>  }
>  
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE