On 11/23/2016 02:28 PM, Andrew Cooper wrote: > >> SVM requires attributes of any NULL segment to be zero. > Where is this claim made? Vol2 recommends that the VMM clear all > attributes, but the wording of the previous paragraph suggests that the > attributes would be ignored in this case. The %ss bug, and some > experimentation on my behalf also indicate that they are ignored.
15.5.1 Basic Operation, Segment State in the VMCB: The VMM should follow these rules when storing segment attributes into the VMCB * For NULL segments, set all attribute bits to zero; otherwise, write the concatenation of bits 55:52 and 47:40 from the original 64-bit (in-memory) segment descriptors. I guess the preceding text is indeed unclear as to whether this is somehow enforced (in which case I am not sure I see the point of having this rule). -boris > >> I don't know about Intel but if it's the same then should we ASSERT this as >> well? > On Intel if unusable is set, all other bits are ignored. > > However, the behaviour of both Intel and AMD is to occasionally set > upper attribute bits. At some point I intend to make emulated segment > loading match d->arch.vendor's behaviour, at which point such an > ASSERT() would definitely trip. > > ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
