> From: Jan Beulich [mailto:jbeul...@suse.com] > Sent: Thursday, December 22, 2016 11:37 PM > > >>> On 22.12.16 at 16:14, <andrew.coop...@citrix.com> wrote: > > On 22/12/16 14:58, Jan Beulich wrote: > >>>>> On 22.12.16 at 15:31, <jbeul...@suse.com> wrote: > >>>>>> On 22.12.16 at 14:47, <andrew.coop...@citrix.com> wrote: > >>>> On 22/12/16 08:37, Jan Beulich wrote: > >>>>> Instead of checking cpu_has_vmx_vmfunc inside the hook, use it to > >>>>> determine whether to install the hook in the first place. > >>>>> > >>>>> Signed-off-by: Jan Beulich <jbeul...@suse.com> > >>>> I am not so sure about this. > >>>> > >>>> vmfunc is reachable in the instruction emulator on hardware which > >>>> doesn't support vmfunc, and there is explicit provision for using vmfunc > >>>> 0 via hypercall on hardware lacking vmfunc support. > >>>> > >>>> Given that the #VE part of altp2m is always emulated architecturally, I > >>>> think there is an argument to be made for also emulating EPTP switching > >>>> architecturally as well. > >>> I don't understand this argumentation: Without the patch, the > >>> hook function checks !cpu_has_vmx_vmfunc (and fails otherwise); > >>> with the patch the hook isn't being put in place when > >>> !cpu_has_vmx_vmfunc, and failure occurs in hvmemul_vmfunc(). > >>> I admit there's the difference in error codes, but we could > >>> certainly make hvmemul_vmfunc() return EXCEPTION when > >>> there's no hook. > >> And btw., installing altp2m_vcpu_update_vmfunc_ve is as pointless > >> in the opposite case, do it bailing early when !cpu_has_vmx_vmfunc. > >> I guess I'll do both changes for a v2. > > > > My argument is that, instead of excluding the hook, the behaviour of the > > emulation path should be made to function sensibly even on hardware > > without vmfunc. > > > > i.e. drop the cpu_has_vmx_vmfunc check and do nothing else. > > Ah, I see. I guess I'll leave that to someone having an environment > to test this. The patch's goal was to not change observable behavior. >
If later we'll have to again get hook always installed (for hardware w/o vmfunc), I'm hesitant to ack this version... Thanks Kevin _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
