netdev - Re: [PATCH] mm: remove zap_page_range and create zap_vma

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Date:   Tue, 14 Feb 2023 19:19:16 -0800 (PST)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     mike.kravetz@...cle.com
CC:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org, netdev@...r.kernel.org,
        Christoph Hellwig <hch@...radead.org>, david@...hat.com,
        mhocko@...e.com, peterx@...hat.com, nadav.amit@...il.com,
        willy@...radead.org, vbabka@...e.cz, riel@...riel.com,
        Will Deacon <will@...nel.org>, mpe@...erman.id.au,
        borntraeger@...ux.ibm.com, dave.hansen@...ux.intel.com,
        brauner@...nel.org, edumazet@...gle.com, akpm@...ux-foundation.org,
        mike.kravetz@...cle.com
Subject:     Re: [PATCH] mm: remove zap_page_range and create zap_vma_pages

On Tue, 03 Jan 2023 16:27:32 PST (-0800), mike.kravetz@...cle.com wrote:
> zap_page_range was originally designed to unmap pages within an address
> range that could span multiple vmas.  While working on [1], it was
> discovered that all callers of zap_page_range pass a range entirely within
> a single vma.  In addition, the mmu notification call within zap_page
> range does not correctly handle ranges that span multiple vmas.  When
> crossing a vma boundary, a new mmu_notifier_range_init/end call pair
> with the new vma should be made.
>
> Instead of fixing zap_page_range, do the following:
> - Create a new routine zap_vma_pages() that will remove all pages within
>   the passed vma.  Most users of zap_page_range pass the entire vma and
>   can use this new routine.
> - For callers of zap_page_range not passing the entire vma, instead call
>   zap_page_range_single().
> - Remove zap_page_range.
>
> [1] https://lore.kernel.org/linux-mm/20221114235507.294320-2-mike.kravetz@oracle.com/
> Suggested-by: Peter Xu <peterx@...hat.com>
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>

[...]

> diff --git a/arch/riscv/kernel/vdso.c b/arch/riscv/kernel/vdso.c
> index e410275918ac..5c30212d8d1c 100644
> --- a/arch/riscv/kernel/vdso.c
> +++ b/arch/riscv/kernel/vdso.c
> @@ -124,13 +124,11 @@ int vdso_join_timens(struct task_struct *task, struct time_namespace *ns)
>  	mmap_read_lock(mm);
>
>  	for_each_vma(vmi, vma) {
> -		unsigned long size = vma->vm_end - vma->vm_start;
> -
>  		if (vma_is_special_mapping(vma, vdso_info.dm))
> -			zap_page_range(vma, vma->vm_start, size);
> +			zap_vma_pages(vma);
>  #ifdef CONFIG_COMPAT
>  		if (vma_is_special_mapping(vma, compat_vdso_info.dm))
> -			zap_page_range(vma, vma->vm_start, size);
> +			zap_vma_pages(vma);
>  #endif
>  	}

Acked-by: Palmer Dabbelt <palmer@...osinc.com> # RISC-V

Thanks!