On Mon, Feb 15, 2016 at 03:41:41PM +0000, Andrew Cooper wrote: > On 15/02/16 15:02, Jan Beulich wrote: > >>>> On 15.02.16 at 15:53, <andrew.coop...@citrix.com> wrote: > >> On 15/02/16 14:50, Jan Beulich wrote: > >>>>>> On 15.02.16 at 15:38, <andrew.coop...@citrix.com> wrote: > >>>> On 15/02/16 09:20, Jan Beulich wrote: > >>>>>>>> On 12.02.16 at 18:42, <andrew.coop...@citrix.com> wrote: > >>>>>> On 12/02/16 17:05, Jan Beulich wrote: > >>>>>>>>>> On 05.02.16 at 14:42, <andrew.coop...@citrix.com> wrote: > >>>>>>>> #define X86_FEATURE_MWAITX ( 3*32+29) /* MWAIT extension > >>>>>> (MONITORX/MWAITX) */ > >>>>>>> Why not exposed to HVM (also for _MWAIT as I now notice)? > >>>>>> Because that is a good chunk of extra work to support. We would need > >>>>>> to > >>>>>> use 4K monitor widths, and extra p2m handling. > >>>>> I don't understand: The base (_MWAIT) feature being exposed to > >>>>> guests today, and kernels making use of the feature when available > >>>>> suggests to me that things work. Are you saying you know > >>>>> otherwise? (And if there really is a reason to mask the feature all of > >>>>> the sudden, this should again be justified in the commit message.) > >>>> PV guests had it clobbered by Xen in traps.c > >>>> > >>>> HVM guests have: > >>>> > >>>> vmx.c: > >>>> case EXIT_REASON_MWAIT_INSTRUCTION: > >>>> case EXIT_REASON_MONITOR_INSTRUCTION: > >>>> [...] > >>>> hvm_inject_hw_exception(TRAP_invalid_op, HVM_DELIVER_NO_ERROR_CODE); > >>>> break; > >>>> > >>>> and svm.c: > >>>> case VMEXIT_MONITOR: > >>>> case VMEXIT_MWAIT: > >>>> hvm_inject_hw_exception(TRAP_invalid_op, > >>>> HVM_DELIVER_NO_ERROR_CODE); > >>>> break; > >>>> > >>>> I don't see how a guest could actually use this feature. > >>> Do you see the respective intercepts getting enabled anywhere? > >>> (I don't outside of nested code, which I didn't check in detail.) > >> Yes - the intercepts are always enabled to prevent the guest actually > >> putting the processor to sleep. > > Hmm, you're right, somehow I've managed to ignore the relevant > > lines grep reported. Yet - how do things work then, without the > > MWAIT feature flag currently getting cleared? > > I have never observed it being used. Do you have some local patches in > the SLES hypervisor? > > There is some gross layer violation in xen/enlighten.c to pretend that > MWAIT is present to trick the ACPI code into evaluating _CST() methods > to report back to Xen. (This is yet another PV-ism which will cause a > headache for a DMLite dom0)
Yes indeed. CC-ing Roger, and Boris. > > ~Andrew > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xen.org > http://lists.xen.org/xen-devel _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
