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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 29/11/11 05:51, Simon Horman wrote:
> 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.

Right.  Sorry.  I should have remembered that basing "who wrote the
patch" on a simple hg log was not a safe bet.

>>> 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.

Fair enough.  I will see what I can do about guaranteeing that the crash
note is aligned in the first place.

Thanks,

-- 
Andrew Cooper - Dom0 Kernel Engineer, Citrix XenServer
T: +44 (0)1223 225 900, http://www.citrix.com


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