Re: [Xen-devel] Unaligned writes on the kexec path

[Simon Horman <horms@xxxxxxxxxxxx>]

Hi Keir, Hi Andrew,

On Mon, Nov 28, 2011 at 08:42:16PM +0000, Keir Fraser wrote:
> On 28/11/2011 14:24, "Andrew Cooper" <andrew.cooper3@xxxxxxxxxx> wrote:
> 
> > Hello,
> > 
> > In c/s 7493bb48d89f, you change the internals of kexec_crash_save_info()
> 
> The patch is by Simon Horman, cc'ed, not me.
> 
> > to reduce unaligned writes, but pass the resulting pointer back to
> > machine_crash_shutdown() which performs writes on the possibly unaligned
> > data structure.  There are also plenty of other writes on the kexec path
> > which are possibly or certainly unaligned.
> > 
> > What is the reason for wanting to reduce unaligned writes?
> 
> The patch is solving an IA64 issue. Machine_crash_shutdown is arch specific.
> 
> > Would a better solution be to just ensure that the crash note itself is
> > properly aligned?
> 
> Could be.

Its a while since I wrote that change, but I believe that aligning
the crash note would resolve the problem that I observed.

As Keir mentions, machine_crash_shutdown() is architecture specific
and I am not sure that I see the ia64 version making any unaligned writes.

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