linux-kernel - Re: [PATCH v3 5/8] mm: Device exclusive memory access

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Message-ID: <2083651.v4LkQjjfQp@nvdebian>
Date:   Thu, 4 Mar 2021 16:20:52 +1100
From:   Alistair Popple <apopple@...dia.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     <linux-mm@...ck.org>, <nouveau@...ts.freedesktop.org>,
        <bskeggs@...hat.com>, <akpm@...ux-foundation.org>,
        <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <dri-devel@...ts.freedesktop.org>, <jhubbard@...dia.com>,
        <rcampbell@...dia.com>, <jglisse@...hat.com>, <hch@...radead.org>,
        <daniel@...ll.ch>
Subject: Re: [PATCH v3 5/8] mm: Device exclusive memory access

On Tuesday, 2 March 2021 11:41:52 PM AEDT Jason Gunthorpe wrote:
> > However try_to_protect() scans the PTEs again under the PTL so checking 
the 
> > mapping of interest actually gets replaced during the rmap walk seems like 
a 
> > reasonable solution. Thanks for the comments.
> 
> It does seem cleaner if you can manage it, the notifier will still be
> needd to program the HW though

Checking during the rmap walk wasn't hard but ultimately pointless. As you say 
a range notifier and lock is required to program the hardware, which requires 
checking the mappings with a mmu notifier sequence anyway.

 - Alistair