linux-kernel - Re: [PATCH RFC 0/3] MAP_POPULATE for device memory

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Message-ID: <YiYrRWMp1akXY8Vb@infradead.org>
Date:   Mon, 7 Mar 2022 07:56:53 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Jarkko Sakkinen <jarkko@...nel.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Nathaniel McCallum <nathaniel@...fian.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-sgx@...r.kernel.org, linux-kernel@...r.kernel.org,
        Florian Fainelli <f.fainelli@...il.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Matthew Auld <matthew.auld@...el.com>,
        Thomas Hellström 
        <thomas.hellstrom@...ux.intel.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Jason Ekstrand <jason@...kstrand.net>,
        Chris Wilson <chris@...is-wilson.co.uk>, G@....fi,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tvrtko Ursulin <tvrtko.ursulin@...el.com>,
        Vasily Averin <vvs@...tuozzo.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        zhangyiru <zhangyiru3@...wei.com>,
        Alexey Gladkov <legion@...nel.org>,
        Alexander Mikhalitsyn <alexander.mikhalitsyn@...tuozzo.com>,
        linux-mips@...r.kernel.org, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, codalist@...a.cs.cmu.edu,
        linux-unionfs@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH RFC 0/3] MAP_POPULATE for device memory

On Mon, Mar 07, 2022 at 03:29:35PM +0200, Jarkko Sakkinen wrote:
> So what would you suggest to sort out the issue? I'm happy to go with
> ioctl if nothing else is acceptable.

PLenty of drivers treat all mmaps as if MAP_POPULATE was specified,
typically by using (io_)remap_pfn_range.  If there any reason to only
optionally have the pre-fault semantics for sgx?  If not this should
be really simple.  And if we have a real need for it to be optional
we'll just need to find a sane way to pass that information to ->mmap.