Re: [Qemu-devel] Windows does not support DataTableRegion at all [was: docs: describe QEMU's VMGenID design]

[Laszlo Ersek]

On 09/14/15 10:24, Igor Mammedov wrote:
> On Sun, 13 Sep 2015 15:34:51 +0300
> "Michael S. Tsirkin" <address@hidden> wrote:
> 
>> On Sun, Sep 13, 2015 at 01:56:44PM +0200, Laszlo Ersek wrote:
>>> As the subject suggests, I have terrible news.
>>>
>>> I'll preserve the full context here, so that it's easy to scroll back to
>>> the ASL for reference.
>>>
>>> I'm also CC'ing edk2-devel, because a number of BIOS developers should
>>> be congregating there.
>>
>> Wow, bravo! It does look like we need to go back to
>> the drawing board.
> I suggest we go back to the last Gal's series
> which is though not universal but a simple and
> straightforward solution.
> That series with comments addressed probably
> is what we need in the end.

I agree (I commented the same on the RHBZ too). The only one requirement
we might not satisfy with that is that the page containing the
generation ID must always be mapped as cacheable. In practice it doesn't
seem to cause issues.

We tried to play nice, but given that (a) the vmgenid doc doesn't
mention a real requirement about the _CRS -- ie. no IO descriptors are
allowed to be in it --, (b) Windows doesn't support DataTableRegion(), I
doubt we could cover our bases 100% anyway. There can be any number of
further hidden requirements, and hidden gaps in ACPI support too, so
it's just business as usual with Windows: whatever works, works, don't
ask why.

Just my opinion of course.

Laszlo

>> The only crazy thing you didn't try is to use
>> an XSDT instead of the DSDT.
>> I find it unlikely that this will help ...
>>
>