Re: [Xen-devel] [PATCH v2 18/30] xen/x86: setup PVHv2 Dom0 ACPI tables

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 26.10.16 at 13:35, <roger.pau@xxxxxxxxxx> wrote:
> On Wed, Oct 12, 2016 at 09:55:44AM -0600, Jan Beulich wrote:
>> Taking an abstract perspective I agree with Andrew that we should
>> be whitelisting here. However, as you already see from the list you
>> provided (which afaict is far from complete wrt ACPI 6.1), this may
>> become cumbersome already initially, not to speak of down the road.
> 
> I've initially used a back-listing approach. We can always change this later 
> on.
> 
> So I've ended up crafting a new MADT, XSDT and RSDP. Note that I'm not 
> crafting a new custom RSDT (and in fact I'm setting rsdt_physical_address = 
> 0 in the RSDP together with revision = 2). This is all placed in RAM stolen 
> from the guest memory map and marked as E820_ACPI, which means that the new 
> RSDP no longer resides below 1MB, and that the Dom0 kernel _must_ use the 
> rsdp_paddr provided in the start info, or else it's going to access the 
> native RSDP.

Hmm, for the RSDP I'm not sure. It might be better if we put it at the
same spot where the host one is, mapping a RAM page there with a
copy of the respective host page data. Otoh your approach allows
Dom0 to still find the real tables if need be, which has both up and
down sides.

>> I'm afraid there are systems where the EBDA is not marked reserved.
>> But maybe there are no current (64-bit capable) ones of that sort.
> 
> Hm, I would say that we leave this as it is currently, and then we can 
> always play more tricks later on if we found any of such systems.

As long as the code is experimental, and there's a note to that effect
which can be easily found (and has to be gone for the code to become
non-experimental), I'm fine with that.

>> > Might it be possible to solve this by identity mapping the first 1MB, and 
>> > marking the RAM regions there as p2m_ram_rw? Or would that create even 
>> > further problems?
>> 
>> Hmm, not sure - the range below 1Mb is marked as MMIO in
>> frame_table[], so there would be a (benign?) conflict at least there.
> 
> As said before, I would leave the current implementation and look into that 
> option if needed.

Same thing here.

Jan

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