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

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Message-ID: <a94973ab83ce48bd85c91397f82d7915@huawei.com>
Date:   Tue, 13 Jul 2021 00:57:59 +0000
From:   "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" 
        <longpeng2@...wei.com>
To:     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

Hi Matthew,

> -----Original Message-----
> From: Matthew Wilcox [mailto:willy@...radead.org]
> Sent: Monday, July 12, 2021 9:30 AM
> To: Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
> <longpeng2@...wei.com>
> Cc: Steven Sistare <steven.sistare@...cle.com>; Anthony Yznaga
> <anthony.yznaga@...cle.com>; linux-kernel@...r.kernel.org;
> linux-mm@...ck.org; Gonglei (Arei) <arei.gonglei@...wei.com>
> Subject: Re: [RFC PATCH 0/5] madvise MADV_DOEXEC
> 
> On Mon, Jul 12, 2021 at 09:05:45AM +0800, Longpeng (Mike, Cloud
> Infrastructure Service Product Dept.) wrote:
> > 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.
> 
> This is dangerous.  There must be an active step for Prog B to accept Prog A's
> ranges into its address space.  Otherwise Prog A could almost completely fill
> Prog B's address space and so control where Prog B places its mappings.  It
> could also provoke a latent bug in Prog B if it doesn't handle address space
> exhaustion gracefully.
> 
> I had a proposal to handle this.  Would it meet your requirements?
> https://lore.kernel.org/lkml/20200730152250.GG23808@casper.infradead.org/

I noticed your proposal of project Sileby and I think it can meet Steven's requirement, but I not sure whether it's suitable for mine because there's no sample code yet, is it in progress ?

According to the abstract of Sileby, I have two questions:
1. Would you plan to support the file-mapping memory sharing ? e.g. Prog A's 4G memory is backend with 2M hugetlb.
2. Does each mshare fd only containe one sharing VMA ? For large memory process (1T~4T in our env), maybe there is hundreds of memory ranges need to be shared, this will take too much fd space if so ?