Re: [Xen-devel] [PATCH v6 4/4] x86/xen: Add "nopv" support for HVM guest

[Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>]

On 2019/7/9 22:54, Boris Ostrovsky wrote:
> On 7/9/19 12:20 AM, Zhenzhong Duan wrote:
> > -const __initconst struct hypervisor_x86 x86_hyper_xen_hvm = {
> > +static uint32_t __init xen_platform_hvm(void)
> > +{
> > +       uint32_t xen_domain = xen_cpuid_base();
> > +       struct x86_hyper_init *h = &x86_hyper_xen_hvm.init;
> > +
> > +       if (xen_pv_domain())
> > +               return 0;
> > +
> > +       if (xen_pvh_domain() && nopv) {
> > +               /* Guest booting via the Xen-PVH boot entry goes here */
> > +               pr_info("\"nopv\" parameter is ignored in PVH guest\n");
> > +               nopv = false;
> > +       } else if (nopv && xen_domain) {
> > +               /*
> > +                * Guest booting via normal boot entry (like via
> > grub2) goes
> > +                * here.
> > +                *
> > +                * Use interface functions for bare hardware if nopv,
> > +                * xen_hvm_guest_late_init is an exception as we need to
> > +                * detect PVH and panic there.
> > +                */
> > +               memcpy(h, (void *)&x86_init.hyper,
> > sizeof(x86_init.hyper));
> And this worked? I'd think it would fail since h points to RO section.
Yes, I have below changes in the patch.

-const __initconst struct hypervisor_x86 x86_hyper_xen_hvm = {
+struct hypervisor_x86 x86_hyper_xen_hvm __initdata = {

> > +               memcpy(&x86_hyper_xen_hvm.runtime, (void
> > *)&x86_platform.hyper,
> > +                      sizeof(x86_platform.hyper));
> > +               h->guest_late_init = xen_hvm_guest_late_init;
> To me this still doesn't look right --- you are making assumptions about
> x86_platform/x86_init.hyper and I don't think you can assume they have
> not been set to point to another hypervisor, for example.
You mean copy_array() calls in init_hypervisor_platform()? But that 
happens after
detect_hypervisor_vendor() shoose out the prefered hypervisor. In detect 
stage,
x86_platform/x86_init.hyper has default value for bare hardware, or I 
missed something?
Just realized I can use memset to zero instead of memcpy which looks 
more rational.
> Would modifying all x86_hyper_xen_hvm's ops (except, I guess,
> xen_hvm_guest_late_init()) to immediately return if nopv is set work?
I think so,  Let me try it.

Zhenzhong


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