linux-kernel - Re: [PATCH 1/2] arm64/hugetlb: Use ptep_get() to get the pte value of a huge page

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Message-ID: <YnqK+Hah0wzMvT1p@FVFYT0MHHV2J.usts.net>
Date:   Tue, 10 May 2022 23:55:36 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc:     catalin.marinas@....com, will@...nel.org, mike.kravetz@...cle.com,
        akpm@...ux-foundation.org, willy@...radead.org,
        anshuman.khandual@....com, christophe.leroy@...roup.eu,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 1/2] arm64/hugetlb: Use ptep_get() to get the pte value
 of a huge page

On Tue, May 10, 2022 at 07:12:52PM +0800, Baolin Wang wrote:
> The original huge_ptep_get() on ARM64 is just a wrapper of ptep_get(),
> which will not take into account any contig-PTEs dirty and access bits.
> Meanwhile we will implement a new ARM64-specific huge_ptep_get()
> interface in following patch, which will take into account any contig-PTEs
> dirty and access bits and only be allowed to pass the head pte of
> a contig-PTE/PMD size page.

IIUC, the huge_ptep_get() you have implemented in patch 2 could
handle non-head pte. It'll return the original pte without potential
AD bit. I admit it is more efficeent to use ptep_get() directly,
but the judgement here should be updated.

With this update.

Reviewed-by: Muchun Song <songmuchun@...edance.com>

Thanks.
 
> Thus change to use ptep_get() to get the pte value of a huge page as
> a preparation.
> 
> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> ---
>  arch/arm64/mm/hugetlbpage.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
> index ca8e65c..be5e2f3 100644
> --- a/arch/arm64/mm/hugetlbpage.c
> +++ b/arch/arm64/mm/hugetlbpage.c
> @@ -172,7 +172,7 @@ static pte_t get_clear_flush(struct mm_struct *mm,
>  			     unsigned long pgsize,
>  			     unsigned long ncontig)
>  {
> -	pte_t orig_pte = huge_ptep_get(ptep);
> +	pte_t orig_pte = ptep_get(ptep);
>  	bool valid = pte_valid(orig_pte);
>  	unsigned long i, saddr = addr;
>  
> @@ -385,7 +385,7 @@ pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
>  {
>  	int ncontig;
>  	size_t pgsize;
> -	pte_t orig_pte = huge_ptep_get(ptep);
> +	pte_t orig_pte = ptep_get(ptep);
>  
>  	if (!pte_cont(orig_pte))
>  		return ptep_get_and_clear(mm, addr, ptep);
> @@ -408,11 +408,11 @@ static int __cont_access_flags_changed(pte_t *ptep, pte_t pte, int ncontig)
>  {
>  	int i;
>  
> -	if (pte_write(pte) != pte_write(huge_ptep_get(ptep)))
> +	if (pte_write(pte) != pte_write(ptep_get(ptep)))
>  		return 1;
>  
>  	for (i = 0; i < ncontig; i++) {
> -		pte_t orig_pte = huge_ptep_get(ptep + i);
> +		pte_t orig_pte = ptep_get(ptep + i);
>  
>  		if (pte_dirty(pte) != pte_dirty(orig_pte))
>  			return 1;
> -- 
> 1.8.3.1
> 
>