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To:     Khalid Aziz <khalid.aziz@oracle.com>, akpm@linux-foundation.org,
        willy@infradead.org, longpeng2@huawei.com, arnd@arndb.de,
        dave.hansen@linux.intel.com, david@redhat.com, rppt@kernel.org,
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References: <cover.1642526745.git.khalid.aziz@oracle.com>
From:   Dave Hansen <dave.hansen@intel.com>
Subject: Re: [RFC PATCH 0/6] Add support for shared PTEs across processes
Message-ID: <e0196efb-9c55-c0f8-c663-b4af44b8ffa4@intel.com>
Date:   Tue, 18 Jan 2022 14:06:20 -0800
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On 1/18/22 1:19 PM, Khalid Aziz wrote:
> This is a proposal to implement a mechanism in kernel to allow
> userspace processes to opt into sharing PTEs. The proposal is to add
> a new system call - mshare(), which can be used by a process to
> create a region (we will call it mshare'd region) which can be used
> by other processes to map same pages using shared PTEs. Other
> process(es), assuming they have the right permissions, can then make
> the mashare() system call to map the shared pages into their address
> space using the shared PTEs.

One thing that went over my head here was that this allowing sharing of
relatively arbitrary *EXISTING* regions.  The mshared'd region might be
anonymous or an plain mmap()'d file.  It can even be a filesystem or
device DAX mmap().

In other words, donors can (ideally) share anything.  Consumers have
must use msharefs to access the donated areas.

Right?

( btw... thanks to willy for the correction on IRC.)