Re: [Xen-devel] [VMI] How to add support for MOV-TO-DRx events ?

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 10.05.19 at 00:02, <andrew.cooper3@xxxxxxxxxx> wrote:
> I think the most important thing to do first is to understand how MOV-DR
> events are intended to be used, and what kind of behaviour we want,
> given that the two can't be shared in practice.

I think they can be shared, but at a significant price: Since DRn
specify linear addresses, at least in shadow mode pages with
guest supplied breakpoints on them could be unmapped, such
that we notice accesses and can then emulate them. But of
course this, as another prereq, requires breakpoints to be
honored in the first place by hvmemul_read() and friends.

So for the time being I assume the two uses being exclusive of
one another is the only viable option. Question in this case is:
What behavior is the guest supposed to observe? DRn writes
simply only going to a place to latch the written values (such
that the written values can be supplied back for reads), and
hence guest specified breakpoints never triggering?

Jan



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