linux-kernel - Re: [RFC][PATCH] Cross Memory Attach

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Message-Id: <20100916105311.CA00.A69D9226@jp.fujitsu.com>
Date:	Thu, 16 Sep 2010 10:58:08 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Bryan Donlan <bdonlan@...il.com>
Cc:	kosaki.motohiro@...fujitsu.com, Avi Kivity <avi@...hat.com>,
	Christopher Yeoh <cyeoh@....ibm.com>,
	linux-kernel@...r.kernel.org,
	Linux Memory Management List <linux-mm@...ck.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC][PATCH] Cross Memory Attach

> On Wed, Sep 15, 2010 at 19:58, Avi Kivity <avi@...hat.com> wrote:
> 
> > Instead of those two syscalls, how about a vmfd(pid_t pid, ulong start,
> > ulong len) system call which returns an file descriptor that represents a
> > portion of the process address space.  You can then use preadv() and
> > pwritev() to copy memory, and io_submit(IO_CMD_PREADV) and
> > io_submit(IO_CMD_PWRITEV) for asynchronous variants (especially useful with
> > a dma engine, since that adds latency).
> >
> > With some care (and use of mmu_notifiers) you can even mmap() your vmfd and
> > access remote process memory directly.
> 
> Rather than introducing a new vmfd() API for this, why not just add
> implementations for these more efficient operations to the existing
> /proc/$pid/mem interface?

As far as I heared from my friend, old HP MPI implementation used /proc/$pid/mem
for this purpose. (I don't know current status). However almost implementation
doesn't do that because /proc/$pid/mem required the process is ptraced.
As far as I understand , very old /proc/$pid/mem doesn't require it. but It changed
for security concern. Then, Anybody haven't want to change this interface because
they worry break security.

But, I don't know what exactly protected "the process is ptraced" check. If anyone
explain the reason and we can remove it. I'm not againt at all.



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