Re: [Xen-devel] gross qemu behavior

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 04.04.14 at 17:32, <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> On Fri, 4 Apr 2014, Jan Beulich wrote:
>> >>> On 04.04.14 at 15:53, <stefano.stabellini@xxxxxxxxxxxxx> wrote:
>> > On Fri, 4 Apr 2014, Jan Beulich wrote:
>> >> No, it should just never appear at the wrong address. As I said above,
>> >> I'd consider it halfway acceptable if it remained mapped despite an
>> >> unmap, but I do think that a proper solution (properly unmapping
>> >> without de-allocating) can and should be found.
>> > 
>> > There is no way to do it today AFAICT.
>> > Would you care of proposing an hypercall that would support this
>> > scenario?
>> 
>> Hypercall? Everything you need is there afaict.
> 
> Maybe I am missing something.
> 
> Moving the PCI ROM to the right place in the guest physmap is easy.
> However how do you think we could unmap the memory (remove it from the
> guest physmap) without deallocating it?
> The only hypercall we have is xc_domain_add_to_physmap at the moment.

XENMEM_remove_from_physmap should be quite suitable here, but
that is not your problem. The problem is that XENMEM_add_to_physmap
requires a GFN to be passed in, i.e. assumes that a page to be mapped
is already mapped somewhere in the guest. (The term "add" in this
context is rather confusing, as in the GMFN map space case the page
isn't being added, but moved.) So indeed there is functionality missing
in the hypervisor.

Jan


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