Re: [Qemu-devel] [PATCH] pc_sysfw: Always use alias for ISA BIOS region

[Jan Kiszka]

On 2012-11-01 19:03, Jordan Justen wrote:
> On Thu, Nov 1, 2012 at 10:21 AM, Jan Kiszka <address@hidden> wrote:
>> On 2012-11-01 18:17, Jan Kiszka wrote:
>>> On 2012-11-01 18:15, Jordan Justen wrote:
>>>> Would the old behavior need to be preserved for pc-1.1 & pc-1.2?
>>>
>>> Why? This is just restoring the older, correct behavior.
>>
>> Err, sorry, there was no difference to the behavior before pflash
>> (unless flash was changed by the guest).
>>
>> Still, I see no point in preserving the current behavior even for compat
>> machine. Which (sane) guest should rely on an inconsistency between the
>> two BIOS mappings after an update?
> 
> I will not claim to know much about this, but I thought the purpose
> was to allow qemu to properly restore old saved VMs.

Ah, I'm getting the problem: the old version created additional RAM,
outside the main memory, and that caused an additional vmsection to be
written. Unfortunate. But I guess we can address this by registering a
dummy vmstate for compat machine types. The content is redundant anyway.

> 
> I agree that the alias in an improvement in machine emulation, and I
> don't think any guest software will rely upon the pc-1.1/pc-1.2
> behavior.
> 
> It is probably worth verifying that the 440 chipset PAM registers are
> still working after this change.

Seabios relies on PAM, so they are apparently still fine. More testing
always welcome, of course.

Jan

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