linux-kernel - Re: [PATCH v2 2/2] x86/mm: implement free pmd/pte page interfaces

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Date:   Thu, 15 Mar 2018 13:09:10 +0530
From:   Chintan Pandya <cpandya@...eaurora.org>
To:     Toshi Kani <toshi.kani@....com>, mhocko@...e.com,
        akpm@...ux-foundation.org, tglx@...utronix.de, mingo@...hat.com,
        hpa@...or.com, bp@...e.de, catalin.marinas@....com
Cc:     x86@...nel.org, wxf.wang@...ilicon.com, guohanjun@...wei.com,
        will.deacon@....com, linux-kernel@...r.kernel.org,
        willy@...radead.org, linux-mm@...ck.org, stable@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 2/2] x86/mm: implement free pmd/pte page interfaces

On 3/14/2018 11:31 PM, Toshi Kani wrote:
> Implement pud_free_pmd_page() and pmd_free_pte_page() on x86, which
> clear a given pud/pmd entry and free up lower level page table(s).
> Address range associated with the pud/pmd entry must have been purged
> by INVLPG.
> 
> fixes: e61ce6ade404e ("mm: change ioremap to set up huge I/O mappings")
> Signed-off-by: Toshi Kani <toshi.kani@....com>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: Matthew Wilcox <willy@...radead.org>
> Cc: <stable@...r.kernel.org>
> ---
>   arch/x86/mm/pgtable.c |   28 ++++++++++++++++++++++++++--
>   1 file changed, 26 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
> index 1eed7ed518e6..34cda7e0551b 100644
> --- a/arch/x86/mm/pgtable.c
> +++ b/arch/x86/mm/pgtable.c
> @@ -712,7 +712,22 @@ int pmd_clear_huge(pmd_t *pmd)
>    */
>   int pud_free_pmd_page(pud_t *pud)
>   {
> -	return pud_none(*pud);
> +	pmd_t *pmd;
> +	int i;
> +
> +	if (pud_none(*pud))
> +		return 1;
> +
> +	pmd = (pmd_t *)pud_page_vaddr(*pud);
> +
> +	for (i = 0; i < PTRS_PER_PMD; i++)
> +		if (!pmd_free_pte_page(&pmd[i]))

This is forced action and no optional. Also, pmd_free_pte_page()
doesn't return 0 in any case. So, you may remove _if_ ?

> +			return 0;
> +
> +	pud_clear(pud);
> +	free_page((unsigned long)pmd);
> +
> +	return 1;
>   }
>   
>   /**
> @@ -724,6 +739,15 @@ int pud_free_pmd_page(pud_t *pud)
>    */
>   int pmd_free_pte_page(pmd_t *pmd)
>   {
> -	return pmd_none(*pmd);
> +	pte_t *pte;
> +
> +	if (pmd_none(*pmd))

This should also check if pmd is already huge. Same for pud ?

> +		return 1;
> +
> +	pte = (pte_t *)pmd_page_vaddr(*pmd);
> +	pmd_clear(pmd);
> +	free_page((unsigned long)pte);
> +
> +	return 1;
>   }
>   #endif	/* CONFIG_HAVE_ARCH_HUGE_VMAP */
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> 

Chintan
-- 
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center,
Inc. is a member of the Code Aurora Forum, a Linux Foundation
Collaborative Project

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