linux-kernel - RE: [RFC PATCH 0/5] madvise MADV

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Message-ID: <6775a78fa70b4868bfd24c750ec24bdd@AcuMS.aculab.com>
Date:   Sat, 14 Aug 2021 20:07:42 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Khalid Aziz' <khalid.aziz@...cle.com>,
        "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" 
        <longpeng2@...wei.com>, Matthew Wilcox <willy@...radead.org>
CC:     Steven Sistare <steven.sistare@...cle.com>,
        Anthony Yznaga <anthony.yznaga@...cle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Gonglei (Arei)" <arei.gonglei@...wei.com>
Subject: RE: [RFC PATCH 0/5] madvise MADV_DOEXEC

...
> > > > Let me describe my use case more clearly (just ignore if you're not
> > > > interested in it):
> > > >
> > > > 1. Prog A mmap() 4GB memory (anon or file-mapping), suppose the
> > > > allocated VA range is [0x40000000,0x140000000)
> > > >
> > > > 2. Prog A specifies [0x48000000,0x50000000) and
> > > > [0x80000000,0x100000000) will be shared by its child.
> > > >
> > > > 3. Prog A fork() Prog B and then Prog B exec() a new ELF binary.
> > > >
> > > > 4. Prog B notice the shared ranges (e.g. by input parameters or
> > > > ...)
> > > > and remap them to a continuous VA range.

Remapping to contiguous VA is going to be difficult in the
general case for (IIRC) VIVT caches.
The required cache coherence may only be attainable by
using uncached mappings.

	David

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