Re: [Xen-devel] [PATCH v2] tools/libxl: mark special pages as reserved in e820 map for PVH

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.11.17 at 12:48, <jgross@xxxxxxxx> wrote:
> On 21/11/17 12:27, Jan Beulich wrote:
>>>>> On 21.11.17 at 12:06, <jgross@xxxxxxxx> wrote:
>>> The "special pages" for PVH guests include the frames for console and
>>> Xenstore ring buffers. Those have to be marked as "Reserved" in the
>>> guest's E820 map, as otherwise conflicts might arise later e.g. when
>>> hotplugging memory into the guest.
>> 
>> Afaict this differs from v1 only in no longer adding the extra entry
>> for HVM. How does this address the concerns raised on v1 wrt spec
>> compliance? v1 having caused problems with hvmloader should not
>> have resulted in simply excluding HVM here. That's even more so
>> because we mean HVM and PVH to converge in the long run - I'd
>> expect that to mean that no clear type distinction would exist
>> anymore on libxl.
> 
> The difference is for HVM the HVMloader is creating the additional
> "Reserved" entry.
> 
>> If you want to reserve Xenstore ring buffer and console page,
>> why don't you reserve just the two (provided of course they
>> live outside of any [fake] PCI device BAR), which then ought to
>> also be compatible with plain HVM?
> 
> For PVH the "mmio" area is starting with the LAPIC and extends up
> to 4GB.

Oh, I see - that's probably okay then (or at least as okay as
libxl having knowledge of the LAPIC base address in the first
place).

Jan


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