linux-kernel - Re: [PATCH 06/14] mm: handle_pte_fault() use pte_offset_map_maywrite

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Message-ID: <6a586524-5116-4eaf-b4f3-c1aea290d7c1@cs-soprasteria.com>
Date: Wed, 21 Aug 2024 09:17:09 +0000
From: LEROY Christophe <christophe.leroy2@...soprasteria.com>
To: Qi Zheng <zhengqi.arch@...edance.com>, "david@...hat.com"
	<david@...hat.com>, "hughd@...gle.com" <hughd@...gle.com>,
	"willy@...radead.org" <willy@...radead.org>, "muchun.song@...ux.dev"
	<muchun.song@...ux.dev>, "vbabka@...nel.org" <vbabka@...nel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>, "rppt@...nel.org"
	<rppt@...nel.org>, "vishal.moola@...il.com" <vishal.moola@...il.com>,
	"peterx@...hat.com" <peterx@...hat.com>, "ryan.roberts@....com"
	<ryan.roberts@....com>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "linuxppc-dev@...ts.ozlabs.org"
	<linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 06/14] mm: handle_pte_fault() use
 pte_offset_map_maywrite_nolock()



Le 21/08/2024 à 10:18, Qi Zheng a écrit :
> In handle_pte_fault(), we may modify the vmf->pte after acquiring the
> vmf->ptl, so convert it to using pte_offset_map_maywrite_nolock(). But
> since we already do the pte_same() check, so there is no need to get
> pmdval to do pmd_same() check, just pass NULL to pmdvalp parameter.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
> ---
>   mm/memory.c | 9 +++++++--
>   1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index 93c0c25433d02..d3378e98faf13 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -5504,9 +5504,14 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
>   		 * pmd by anon khugepaged, since that takes mmap_lock in write
>   		 * mode; but shmem or file collapse to THP could still morph
>   		 * it into a huge pmd: just retry later if so.
> +		 *
> +		 * Use the maywrite version to indicate that vmf->pte will be
> +		 * modified, but since we will use pte_same() to detect the
> +		 * change of the pte entry, there is no need to get pmdval.
>   		 */
> -		vmf->pte = pte_offset_map_nolock(vmf->vma->vm_mm, vmf->pmd,
> -						 vmf->address, &vmf->ptl);
> +		vmf->pte = pte_offset_map_maywrite_nolock(vmf->vma->vm_mm,
> +							  vmf->pmd, vmf->address,
> +							  NULL, &vmf->ptl);

This might be the demonstration that the function name is becoming too long.

Can you find shorter names ?

>   		if (unlikely(!vmf->pte))
>   			return 0;
>   		vmf->orig_pte = ptep_get_lockless(vmf->pte);