[SeaBIOS] seabios 0.6.1 regression

Alexander Graf agraf at suse.de
Tue Nov 16 15:17:20 CET 2010

On 16.11.2010, at 15:15, Avi Kivity wrote:

> On 11/16/2010 03:19 PM, Alexander Graf wrote:
>> >>>
>> >>
>> >>  Rewriting it to use inb / stos works (jecxz ; insb; loop doesn't) so it looks like a kernel bug in insb emulation.
>> >>
>> >
>> >  Turns out is was a subtle bug in the tpr optimization we do for Windows XP.  The problem happens when we load the vapic option rom from the firmware config interface.  With inb / movb, writing the vapic area happens in guest context, which the kernel is prepared to handle.  


>> With insb, the write happens from kvm, which is then undone on the next entry, leading to the tpr being set to a high value.
>> Shouldn't the vapic area be mapped in on demand? Then we could map it on option rom init time and everyone's happy.
> Mapped in? It's an option rom.

According to your wording, the kernel handles writes to the vapic area. If the vapic area is only made special after initialization of the option rom, we wouldn't have this issue.


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