linux-kernel - Re: [PATCH 4/7] mm/gup: introduce the FOLL_SAME

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Message-ID: <ZD1GGiHBOj1mRDu4@nvidia.com>
Date:   Mon, 17 Apr 2023 10:14:02 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Lorenzo Stoakes <lstoakes@...il.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH 4/7] mm/gup: introduce the FOLL_SAME_FILE GUP flag

On Sat, Apr 15, 2023 at 12:27:40AM +0100, Lorenzo Stoakes wrote:
> This flag causes GUP to assert that all VMAs within the input range possess
> the same vma->vm_file. If not, the operation fails.
> 
> This is part of a patch series which eliminates the vmas parameter from the
> GUP API, implementing the one remaining assertion within the entire kernel
> that requires access to the VMAs associated with a GUP range.
> 
> Signed-off-by: Lorenzo Stoakes <lstoakes@...il.com>
> ---
>  include/linux/mm_types.h |  2 ++
>  mm/gup.c                 | 16 ++++++++++++----
>  2 files changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 3fc9e680f174..84d1aec9dbab 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -1185,6 +1185,8 @@ enum {
>  	FOLL_PCI_P2PDMA = 1 << 10,
>  	/* allow interrupts from generic signals */
>  	FOLL_INTERRUPTIBLE = 1 << 11,
> +	/* assert that the range spans VMAs with the same vma->vm_file */
> +	FOLL_SAME_FILE = 1 << 12,

I hope we don't add this flag, but it needs to be rejected in
internal_get_user_pages_fast()

Jason