Re: Kexec, DMA, and SMP

Suparna Bhattacharya
2003-02-11T12:40:03Z

On Mon, Feb 10, 2003 at 10:56:43AM -0700, Eric W. Biederman wrote:
> Suparna Bhattacharya <suparna@in.ibm.com> writes:
[snip]
>
> Not primarily. Instead I am trying to address the possibility that
> DMA is overwriting the recovery code due to a device not being shutdown
> properly. Though it would happen to cover many cases of the wrong
> memory address being passed to a device.
>
[snip]
>
> The other piece that a reserved area of memory is that you can
> simplify the other cases because you don't need to do anything
> before the dump because everything is preserved.
>
[snip]

> Yes, for the same reasons. I am definitely not trying to address the
> case of buggy hardware.
>
[snip]
>
> And I am certain that with a preserved memory area we can
> preserve everything without compression.
>

OK, I see where you are coming from. It is an interesting
possibility, if you know how to pull it off for various
architectures, and the working area that the new kernel needs
to do operate to the extent of issuing the writeout is not
too big (i.e. doesn't take away too much memory from the
operational kernel). Perhaps we could hide this memory from
the normal kernel virtual address space most of the time, so
its less susceptable to software corruption (i.e. besides
physical access via DMA).

At the same time we do want to quiesce / stop the DMA as
soon as possible to get a dump that reflects the
contents of memory at the concerned instant as closely as
possible. And in the buggy case we want to stop any
malfunctioning DMA (writes) immediately to minimize
damage.

Regards
Suparna

--
Suparna Bhattacharya (suparna@in.ibm.com)
Linux Technology Center
IBM Software Labs, India