Re: [Xen-devel] [PATCH RFC v2 02/12] x86: don't use hypervisor stack size for dumping guest stacks

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.01.18 at 10:58, <jgross@xxxxxxxx> wrote:
> On 23/01/18 10:26, Jan Beulich wrote:
>>>>> On 22.01.18 at 13:32, <jgross@xxxxxxxx> wrote:
>>> show_guest_stack() and compat_show_guest_stack() stop dumping the
>>> stack of the guest whenever its virtual address reaches the same
>>> alignment which is used for the hypervisor stacks.
>>>
>>> Remove this arbitrary limit and try to dump a fixed number of lines
>>> instead.
>> 
>> Hmm, I can see your point, but before looking at the change in detail
>> I think we need to agree on what behavior we want. Dumping
>> arbitrary data as if it was a part of the stack isn't very helpful, limiting
>> the risk of which is, I think, the reason for the way things currently
>> work (assuming that guest kernels won't have stacks larger than Xen
>> itself, and that they too would align them). What would perhaps be
>> better is for the guest to supply information about the restrictions it
>> enforces on its stacks, which Xen could then use here. In the
>> absence of such hints using the values currently being used would
>> possibly make sense.
> 
> Currently the stack dump will have the same fixed number of lines as
> with my patch. I'm only removing the premature end of dumping whenever
> the stack address crosses a 32kB boundary. Linux 64 bit pv guests are
> using 16kB stack size. So using this boundary would be more natural.

IOW your change converts a 50:50 chance of dumping non-stack
data to 100% (all in case the stack pointer isn't far away from the
stack start).

Jan


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