linux-kernel - Re: [RFC PATCH 0/6] Add support for shared PTEs across processes

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Message-ID: <e0196efb-9c55-c0f8-c663-b4af44b8ffa4@intel.com>
Date:   Tue, 18 Jan 2022 14:06:20 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Khalid Aziz <khalid.aziz@...cle.com>, akpm@...ux-foundation.org,
        willy@...radead.org, longpeng2@...wei.com, arnd@...db.de,
        dave.hansen@...ux.intel.com, david@...hat.com, rppt@...nel.org,
        surenb@...gle.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC PATCH 0/6] Add support for shared PTEs across processes

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.)