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Message-ID: <ZEwC+viAMJ0vEpgU@nvidia.com>
Date: Fri, 28 Apr 2023 14:31:38 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: David Hildenbrand <david@...hat.com>
Cc: "Kirill A . Shutemov" <kirill@...temov.name>,
Peter Xu <peterx@...hat.com>,
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Subject: Re: [PATCH v5] mm/gup: disallow GUP writing to file-backed mappings
by default
On Fri, Apr 28, 2023 at 07:02:22PM +0200, David Hildenbrand wrote:
> > No. VMA cannot get away before PTEs are unmapped and TLB is flushed. And
> > TLB flushing is serialized against GUP_fast().
>
> The whole CONFIG_MMU_GATHER_RCU_TABLE_FREE handling makes the situation more
> complicated.
Yeah, you have to think of gup_fast as RCU with a hacky pre-RCU implementation
on most architectures.
We could make page->mapping safe under RCU, for instance.
Jason
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