>>> On 15.02.17 at 12:21, <t...@xen.org> wrote: > At 01:18 -0700 on 15 Feb (1487121525), Jan Beulich wrote: >> >>> On 14.02.17 at 18:33, <t...@xen.org> wrote: >> >> TBD: Do we really want to re-init the TSS every time we are about to >> >> use it? >> > >> > No - I think we should init it when the guest writes the param(s) and >> > leave it at that. Hvmloader marks it as reserved so the guest should >> > know better than to write to it, and we can't protect it against all >> > the possible ways the guest could break itself. >> > >> > If you do want to re-init it more often, then I think it would still >> > be better to legacy guests' (lack of a) size limit once, when the guest >> > writes the base param. >> >> The only problem with this being that at the time the base gets >> written we don't know the size yet (nor whether the guest is >> going to write it), and hence we don't know how must space to >> initialize. The lower limit we enforce on the size (if being set) is >> below the 128 byte default for old guests. > > Why not make the lower limit 128? I'd happily exchange simpler > hypervisor code for the theoretical case of a guest that needs to run > realmode code and cares about those few bytes.
Actually there's one more issue with doing it when the parameter is being set: If a guest wanted to move the TSS (the parameter isn't one-shot after all), we can't use the old value of the other parameter when the first of the two is being changed. Of course we could make both parameters one-shot, but this would again seem arbitrary. So I think the better model is to record when either parameter changed, and do the initialization just once after that. Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
