From: Nathan Lynch <ntl@pobox•com>
To: Oren Laadan <orenl@cs•columbia.edu>
Cc: containers@lists•osdl.org, linuxppc-dev@ozlabs•org
Subject: Re: [PATCH 1/3] powerpc: bare minimum checkpoint/restart implementation
Date: Tue, 17 Feb 2009 01:03:55 -0600 [thread overview]
Message-ID: <20090217010355.58afd5cf@thinkcentre.lan> (raw)
In-Reply-To: <20090129214035.GB6913@localdomain>
Nathan Lynch <ntl@pobox•com> wrote:
>
> Oren Laadan wrote:
> >
> > Nathan Lynch wrote:
> > >
> > > What doesn't work:
> > > * restarting a 32-bit task from a 64-bit task and vice versa
> >
> > Is there a test to bail if we attempt to checkpoint such tasks ?
>
> No, but I'll add one if it looks too hard to fix for the next round.
Unfortunately, adding a check for this is hard.
The "point of no return" in the restart path is cr_read_mm, which tears
down current's address space. cr_read_mm runs way before cr_read_cpu,
which is the only restart method I've implemented for powerpc so far.
So, checking for this condition in cr_read_cpu is too late if I want
restart(2) to return an error and leave the caller's memory map
intact. (And I do want this: restart should be as robust as execve.)
Well okay then, cr_read_head_arch seems to be the right place in the
restart sequence for the architecture code to handle this. However,
cr_write_head_arch (which produces the buffer that cr_read_head_arch
consumes) is not provided a reference to the task to be checkpointed,
nor can it assume that it's operating on current. I need a reference
to a task before I can determine whether it's running in 32- or 64-bit
mode, or using the FPU, Altivec, SPE, whatever.
In any case, mixing 32- and 64-bit tasks across restart is something I
eventually want to support, not reject. But the problem I've outlined
applies to FPU state and vector extensions (VMX, SPE), as well as
sanity-checking debug register (DABR) contents. We'll need to be able
to error out gracefully from restart when a checkpoint image specifies a
feature unsupported by the current kernel or hardware. But I don't see
how to do it with the current architecture. Am I missing something?
next prev parent reply other threads:[~2009-02-17 7:04 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-01-28 22:41 [RFC/PATCH 0/3] checkpoint/restart for powerpc Nathan Lynch
2009-01-28 22:41 ` [PATCH 1/3] powerpc: bare minimum checkpoint/restart implementation Nathan Lynch
2009-01-29 6:41 ` Oren Laadan
2009-01-29 21:40 ` Nathan Lynch
2009-01-30 0:11 ` Oren Laadan
2009-01-30 20:25 ` Nathan Lynch
2009-02-17 7:03 ` Nathan Lynch [this message]
2009-02-17 20:02 ` [PATCH 1/3 v2] powerpc: heckpoint/restart implementation Nathan Lynch
2009-02-24 19:58 ` [PATCH 1/3] powerpc: bare minimum checkpoint/restart implementation Serge E. Hallyn
2009-02-24 21:11 ` Nathan Lynch
2009-03-13 3:36 ` Oren Laadan
2009-03-13 3:31 ` Oren Laadan
2009-03-13 15:42 ` Cedric Le Goater
2009-03-16 18:37 ` Nathan Lynch
2009-03-17 6:55 ` Cedric Le Goater
2009-03-18 9:15 ` Oren Laadan
2009-01-30 4:01 ` Serge E. Hallyn
2009-01-30 3:55 ` Serge E. Hallyn
2009-02-04 3:39 ` Benjamin Herrenschmidt
2009-02-04 15:54 ` Serge E. Hallyn
2009-02-04 20:58 ` Benjamin Herrenschmidt
2009-02-04 23:44 ` Oren Laadan
2009-02-05 0:16 ` Benjamin Herrenschmidt
2009-02-05 3:30 ` Oren Laadan
2009-02-05 16:09 ` Serge E. Hallyn
2009-02-05 21:01 ` Benjamin Herrenschmidt
2009-01-28 22:41 ` [PATCH 2/3] powerpc: wire up checkpoint and restart syscalls Nathan Lynch
2009-01-28 22:41 ` [PATCH 3/3] allow checkpoint/restart on powerpc Nathan Lynch
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