Re: How to reserve guest physical region for ACPI

[Xiao Guangrong <guangrong.xiao@linux.intel.com>]

On 01/06/2016 12:43 AM, Michael S. Tsirkin wrote:

>>> Yes - if address is static, you need to put it outside
>>> the table. Can come right before or right after this.
>>>
>>>> Also if OperationRegion() is used, then one has to patch
>>>> DefOpRegion directly as RegionOffset must be Integer,
>>>> using variable names is not permitted there.
>>>
>>> I am not sure the comment was understood correctly.
>>> The comment says really "we can't use DataTableRegion
>>> so here is an alternative".
>> so how are you going to access data at which patched
>> NameString point to?
>> for that you'd need a normal patched OperationRegion
>> as well since DataTableRegion isn't usable.
>
> For VMGENID you would patch the method that
> returns the address - you do not need an op region
> as you never access it.
>
> I don't know about NVDIMM. Maybe OperationRegion can
> use the patched NameString? Will need some thought.

The ACPI spec says that the offsetTerm in OperationRegion
is evaluated as Int, so the named object is allowed to be
used in OperationRegion, that is exact what my patchset
is doing (http://marc.info/?l=kvm&m=145193395624537&w=2):

+    dsm_mem = aml_arg(3);
+    aml_append(method, aml_store(aml_call0(NVDIMM_GET_DSM_MEM), dsm_mem));

+    aml_append(method, aml_operation_region("NRAM", AML_SYSTEM_MEMORY,
+                                            dsm_mem, TARGET_PAGE_SIZE));

We hide the int64 object which is patched by BIOS in the method,
NVDIMM_GET_DSM_MEM, to make windows XP happy.

However, the disadvantages i see are:
a) as Igor pointed out, we need a way to tell QEMU what is the patched
    address, in NVDIMM ACPI, we used a 64 bit IO ports to pass the address
    to QEMU.

b) BIOS allocated memory is RAM based so it stops us to use MMIO in ACPI,
    MMIO is the more scalable resource than IO port as it has larger region
    and supports 64 bits operation.