[SeaBIOS] vgabios -> seabios breaks (my) 16-bit applications
Paolo Bonzini
pbonzini at redhat.com
Mon Jan 12 20:00:24 CET 2015
> > No, KVM hides the fact that you are in protected mode. EMM386 would be
> > affected, but then it is not impossible for old programs to require
> > disabling it.
>
> I was under the vague impression that kvm uses VM86 mode to run 16bit
> code on some Intel chipsets. The SMSW instruction isn't privileged so
> I didn't think it could be hidden.
It isn't privileged indeed (nice trick in fact!), but that doesn't matter
for VT-x extensions.
Old processors let you run the processor in VMX non-root mode (i.e. as a VM)
only in protected mode, so KVM uses VM86 when the processor is in real mode
(and uses an interpreter while in big real mode or during real<->protected mode
transitions).
But all the bells and whistles of VMX still apply, including the ability to
fake the value of CR0 for both MOV and [LS]MSW instructions.
Paolo
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