Re: [PATCH 2/6] vTPM: add HVM_PARAM_STUBDOM_VTPM parameter for HVM virtual machine

["Xu, Quan" <quan.xu@intel.com>]

> -----Original Message-----
> From: Stefano Stabellini [mailto:stefano.stabellini@eu.citrix.com]
> Sent: Thursday, October 30, 2014 9:35 PM
> To: Andrew Cooper
> Cc: Xu, Quan; xen-devel@lists.xen.org; ian.jackson@eu.citrix.com; tim@xen.org;
> keir@xen.org; ian.campbell@citrix.com; jbeulich@suse.com
> Subject: Re: [Xen-devel] [PATCH 2/6] vTPM: add
> HVM_PARAM_STUBDOM_VTPM parameter for HVM virtual machine
> 
> On Thu, 30 Oct 2014, Andrew Cooper wrote:
> > On 30/10/14 12:05, Xu, Quan wrote:
> > >
> > >> -----Original Message-----
> > >> From: Andrew Cooper [mailto:andrew.cooper3@citrix.com]
> > >> Sent: Thursday, October 30, 2014 7:50 PM
> > >> To: Xu, Quan; xen-devel@lists.xen.org
> > >> Cc: keir@xen.org; ian.campbell@citrix.com; tim@xen.org;
> > >> ian.jackson@eu.citrix.com; jbeulich@suse.com
> > >> Subject: Re: [Xen-devel] [PATCH 2/6] vTPM: add
> > >> HVM_PARAM_STUBDOM_VTPM parameter for HVM virtual machine
> > >>
> > >> On 30/10/14 07:38, Quan Xu wrote:
> > >>> Signed-off-by: Quan Xu <quan.xu@intel.com>
> > >> What is the purpose of this parameter?  A patch like this is
> > >> currently unacceptable, especially as the libxl hunk indicates that
> > >> the parameter name does not match whatever information you are putting
> into it.
> > >>
> > > Thanks for your suggestion.
> > > This parameter tell the Qemu whether to register Qemu vTPM frontend in
> xen_hvm_init().
> > > Qemu will get the parameter value by xc_get_hvm_param(). How can I
> change it?
> >
> > This is surely something which should be a command line parameter to
> > qemu, or perhaps for qemu to read out of xenstore.
> >
> > An HVM param is entirely inappropriate for this purpose, in my opinion.
> 
> I agree that an HVM param for this might not the best way to do it, but I can see
> why Quan did it that way as we already have a few key parameters passed to
> QEMU that way.
> 
> A QEMU command line option, QMP command or xenstore key would be better.

If hvm param is not the best way, I think xenstore key would be better.

Below is part of Qemu patch, that's why I add HVM_PARAM_STUBDOM_VTPM param.
xen_vtpm_register() is similar to xen_be_register()

### Qemu : xen_hvm_init() [xen-hvm.c]###
+#ifdef CONFIG_TPM_XENSTUBDOMS
+    xc_get_hvm_param(xen_xc, xen_domid, HVM_PARAM_STUBDOM_VTPM, &stubdom_vtpm);
+    if (stubdom_vtpm) {
+        xen_vtpm_register(&xen_vtpmdev_ops);
+    }
+#endif

    xen_be_register("console", &xen_console_ops);
    xen_be_register("vkbd", &xen_kbdmouse_ops);
    xen_be_register("qdisk", &xen_blkdev_ops);
    xen_read_physmap(state);
##### Qemu ####


Quan