> From: Andrew Cooper [mailto:andrew.coop...@citrix.com] > Sent: Saturday, June 9, 2018 2:49 AM > > Currently, the VMX_MSR_GUEST type maintains completely symmetric > guest load > and save lists, by pointing VM_EXIT_MSR_STORE_ADDR and > VM_ENTRY_MSR_LOAD_ADDR > at the same page, and setting VM_EXIT_MSR_STORE_COUNT and > VM_ENTRY_MSR_LOAD_COUNT to the same value. > > However, for MSRs which we won't let the guest have direct access to, > having > hardware save the current value on VMExit is unnecessary overhead. > > To avoid this overhead, we must make the load and save lists asymmetric. > By > making the entry load count greater than the exit store count, we can > maintain > two adjacent lists of MSRs, the first of which is saved and restored, and the > second of which is only restored on VMEntry. > > For simplicity: > * Both adjacent lists are still sorted by MSR index. > * It undefined behaviour to insert the same MSR into both lists. > * The total size of both lists is still limited at 256 entries (one 4k page). > > Split the current msr_count field into msr_{load,save}_count, and introduce > a > new VMX_MSR_GUEST_LOADONLY type, and update vmx_{add,find}_msr() > to calculate > which sublist to search, based on type. VMX_MSR_HOST has no logical > sublist, > whereas VMX_MSR_GUEST has a sublist between 0 and the save count, > while > VMX_MSR_GUEST_LOADONLY has a sublist between the save count and > the load > count. > > One subtle point is that inserting an MSR into the load-save list involves > moving the entire load-only list, and updating both counts. > > Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com> > Reviewed-by: Jan Beulich <jbeul...@suse.com> > Reviewed-by: Roger Pau Monné <roger....@citrix.com>
Acked-by: Kevin Tian <kevin.t...@intel.com> _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
