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Re: [PATCH] hvmloader: flip "ACPI data" to ACPI NVS type for ACPI table region

  • To: Jan Beulich <jbeulich@xxxxxxxx>
  • From: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
  • Date: Wed, 14 Oct 2020 01:42:15 +0100
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  • Cc: <xen-devel@xxxxxxxxxxxxxxxxxxxx>, <andrew.cooper3@xxxxxxxxxx>, <roger.pau@xxxxxxxxxx>, <wl@xxxxxxx>, <iwj@xxxxxxxxxxxxxx>
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On 13/10/2020 16:54, Jan Beulich wrote:
> On 13.10.2020 17:47, Igor Druzhinin wrote:
>> On 13/10/2020 16:35, Jan Beulich wrote:
>>> On 13.10.2020 14:59, Igor Druzhinin wrote:
>>>> On 13/10/2020 13:51, Jan Beulich wrote:
>>>>> As a consequence I think we will also want to adjust Xen itself to
>>>>> automatically disable ACPI when it ends up consuming E801 data. Or
>>>>> alternatively we should consider dropping all E801-related code (as
>>>>> being inapplicable to 64-bit systems).
>>>> I'm not following here. What Xen has to do with E801? It's a SeaBIOS 
>>>> implemented
>>>> call that happened to be used by QEMU option ROM. We cannot drop it from 
>>>> there
>>>> as it's part of BIOS spec.
>>> Any ACPI aware OS has to use E820 (and nothing else). Hence our
>>> own use of E801 should either be dropped, or lead to the
>>> disabling of ACPI. Otherwise real firmware using logic similar
>>> to SeaBIOS'es (but hopefully properly accounting for holes)
>>> could make us use ACPI table space as normal RAM.
>> It's not us using it - it's a boot loader from QEMU in a form of option ROM
>> that works in 16bit pre-OS environment which is not OS and relies on e801 
>> BIOS call.
>> I'm sure any ACPI aware OS does indeed use E820 but the problem here is not 
>> an OS.
>> The option ROM is loaded using fw_cfg from QEMU so it's not our code. 
>> Technically
>> it's one foreign code (QEMU boot loader) talking to another foreign code 
>> (SeaBIOS)
>> which provides information based on E820 that we gave them.
>> So I'm afraid decision to dynamically disable ACPI (whatever you mean by 
>> this)
>> cannot be made by sole usage of this call by a pre-OS boot loader.
> I guess this is simply a misunderstanding. I'm not talking about
> your change or hvmloader or the boot loader at all. I was merely
> noticing a consequence of your findings on the behavior of Xen
> itself: Use of ACPI and use of E801 are exclusive of one another.

Sorry, yes. I forgot e801 is also used by Xen as an alternative to e820.




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