SVM: Can we read back all segment attributes?

SVM: Can we read back all segment attributes?

[Jan Kiszka]

Hi Jörg,

a question about how to interpret the SVM spec popped up because of a
problems with running KVM on top of VMware: We currently read the G bit
of all segments except CS back from the VMCB (svm_get_segment). VMware
does not seem to support this while real hardware is practically fine.
So I received some KVM patch from them to apply the CS strategy (use the
limit to define G) for all segments.

Reading section 15.5.1, one could base this on the sentence ("Segment
State in the VMCB"): "However, only some of the attribute bits are
actually observed by hardware, depending on the segment register in
question: ..." Then follows a list that does not include G. That
definitely means hardware does not read the G bit - but does it always
update it when the guest loads a different segment?

And if G is not guaranteed to be updated, what about the other bits we
currently read back? Are there some that are affected by these
exceptions as well?

Jan

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