Re: [Xen-devel] Xen-unstable 4.8: HVM domain_crash called from emulate.c:144 RIP: c000:[<000000000000336a>]

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.06.16 at 16:56, <boris.ostrovsky@xxxxxxxxxx> wrote:
> On 06/15/2016 10:39 AM, Jan Beulich wrote:
>>>>> On 15.06.16 at 16:32, <boris.ostrovsky@xxxxxxxxxx> wrote:
>>> So perhaps we shouldn't latch data for anything over page size.
>> But why? What we latch is the start of the accessed range, so
>> the repeat count shouldn't matter?
> 
> Because otherwise we won't emulate full stos (or movs) --- we truncate
> *reps to fit into a page, don't we?

That merely causes the instruction to get restarted (with a smaller
rCX).

> And then we fail the completion check.
> 
> And we should latch only when we don't cross page boundary, not just
> when we are under 4K. Or maybe it's not that we don't latch it. It's
> that we don't use latched data if page boundary is being crossed.

Ah, I think that's it: When we hand a batch to qemu which crosses
a page boundary and latch the start address translation, upon
retry (after qemu did its job) we'd wrongly reduce the repeat count
because of finding the start address in the cache. So indeed I think
it should be the latter: Not using an available translation is likely
better than breaking up a large batch we hand to qemu. Paul, what
do you think?

In any event I'll revert the patch from staging, until I can provide
a fixed one.

Jan


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