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Subject: Re: [OMPI devel] Cross Memory Attach: What am I Missing?
From: Gutierrez, Samuel K (samuel_at_[hidden])
Date: 2012-10-19 15:30:16

Hi Chris,

Thanks for all the info. Below is what can go into the FAQ. Any suggestions?

I'm trying to use the Cross Memory Attach (CMA) capability within the
shared-memory (sm) BTL, but am getting: "mca_btl_sm_get_sync: process_vm_readv
failed: 1." Why am I seeing this error message?

This may be due to insufficient permissions. CMA's usage requirements are
exactly the same as those required to successfully perform a ptrace wtih PTRACE_ATTACH.

On some systems, a modification to /etc/sysctl.d/10-ptrace.conf is required.

kernel.yama.ptrace_scope = 1


kernel.yama.ptrace_scope = 0

and restart your system so the change can take effect.


From: devel-bounces_at_[hidden] [devel-bounces_at_[hidden]] on behalf of Christopher Yeoh [cyeoh_at_[hidden]]
Sent: Thursday, October 18, 2012 5:57 PM
To: devel_at_[hidden]
Subject: Re: [OMPI devel] Cross Memory Attach: What am I Missing?

Hi Sam,

On Thu, 18 Oct 2012 15:08:59 +0000
"Gutierrez, Samuel K" <samuel_at_[hidden]> wrote:
> I really appreciate your pointing me in the right direction. It turns
> out that on this particular system had /etc/sysctl.d/10-ptrace.conf
> was set to 1. Changing this to 0 fixed the problem. I'm not sure if
> this is the best way of getting things to work, but is sufficient for
> my purposes.

Yes I think this is the best way to do it. The kernel side
implementation of CMA does the same permission checking as as ptrace
(checks to see if PTRACE_MODE_ATTACH would be permitted). A value of 1
in that config file only allows you to ptrace direct child processes,
whereas a 0 removes that restriction.

You still need to either have CAP_SYS_PTRACE (eg am probably root) or
have the same UID/GID as the target. So from a security point of view
the only extra risk you have exposed your system to are bugs that may
exist in the ptrace or CMA implementations.



> Thanks!
> Sam
> ________________________________
> From: devel-bounces_at_[hidden] [devel-bounces_at_[hidden]] on
> behalf of George Bosilca [bosilca_at_[hidden]] Sent: Thursday,
> October 18, 2012 7:44 AM To: Open MPI Developers
> Subject: Re: [OMPI devel] Cross Memory Attach: What am I Missing?
> Check the permissions granted by pam. Look in the /etc/security to
> check for any type of restrictions.
> george.
> On Oct 17, 2012, at 23:30 , "Gutierrez, Samuel K"
> <samuel_at_[hidden]<mailto:samuel_at_[hidden]>> wrote:
> Hi,
> I'm trying to run with CMA support, but process_vm_readv is failing
> with EPERM when trying to use it as a regular user (everything seems
> to work fine as root). I've looked around for some solutions, but I
> can't seem to find what I'm looking for. The documentation states
> that the target and source processes need to have the same GID and
> UID to work properly. It appears that they do, so my feeling is that
> I'm missing something.
> Any help is greatly appreciated.
> Thanks,
> Sam
> _______________________________________________
> devel mailing list
> devel_at_[hidden]<mailto:devel_at_[hidden]>

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