Re: [Xen-devel] Inconsistent use of set_context_data()?

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.10.16 at 14:44, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> On 10/05/2016 03:29 PM, Jan Beulich wrote:
>>>>> On 05.10.16 at 14:22, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>>>> what's the point of this being used by hvmemul_read() and
>>>> hvmemul_cmpxchg(), but (namely but not limited to) not by
>>>> hvmemul_write()?
>>>
>>> To do introspection work, we sometimes need to modify the guest memory,
>>> and there are cases, namely during hibernate / resume of Windows guests,
>>> when we need to serve the "old" version of that memory to the current
>>> instruction reading from it for the process to work reliably.
>>>
>>> The design choice here has been that the introspection application is
>>> smart enough to handle writes (after all, it is the one managing the
>>> buffer sent via vm_event reply), so it is intended behaviour.
>> 
>> Well - the confusing thing is that for cmpxchg it's the value to be
>> written which gets altered, not the value to be compared against,
>> i.e. it acts as if set_context_data() was also intended to be
>> present in hvmemul_write().
> 
> That's an accident, in hvmemul_cmpxchg() p_old is not being used at all
> so IIRC I've simply latched onto p_new. All we're interested in are
> reads from the supplied buffer overriding the guest's actual memory.

So am I to understand you'll submit a patch replacing p_old with
p_new there (which would have the same effect as simply deleting
that code, except for the doc aspect)?

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel