Re: [Xen-devel] [PATCH 0/2] MMIO emulation fixes

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.08.18 at 12:56, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 16/08/18 11:29, Jan Beulich wrote:
>> Following some further discussion with Andrew, he looks to be
>> convinced that the issue is to be fixed in the balloon driver,
>> which so far (intentionally afaict) does not remove the direct
>> map entries for ballooned out pages in the HVM case. I'm not
>> convinced of this, but I'd nevertheless like to inquire whether
>> such a change (resulting in shattered super page mappings)
>> would be acceptable in the first place.
> 
> We don't tolerate anything else in the directmap pointing to
> invalid/unimplemented frames.  Why should ballooning be any different?

Because ballooning is something virtualization specific, which
doesn't have any equivalent on bare hardware (memory hot
unplug doesn't come quite close enough imo, not the least
because that doesn't work on a page granular basis). Hence
we're to define the exact behavior here, and hence such a
definition could as well include special behavior of accesses
to the involved guest-physical addresses.

Jan



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