Re: [Xen-devel] [PATCH 7/8] x86/hyperv: retrieve vp_index from Hyper-V

[Wei Liu <wl@xxxxxxx>]

On Fri, Jan 03, 2020 at 11:11:39AM +0000, Paul Durrant wrote:
> On Sun, 29 Dec 2019 at 18:35, Wei Liu <wl@xxxxxxx> wrote:
> >
> > This will be useful when invoking hypercall that targets specific
> > vcpu(s).
> >
> > Signed-off-by: Wei Liu <liuwe@xxxxxxxxxxxxx>
> > ---
> >  xen/arch/x86/guest/hyperv/hyperv.c | 12 ++++++++++++
> >  xen/include/asm-x86/guest/hyperv.h |  1 +
> >  2 files changed, 13 insertions(+)
> >
> > diff --git a/xen/arch/x86/guest/hyperv/hyperv.c 
> > b/xen/arch/x86/guest/hyperv/hyperv.c
> > index 67667936e9..da3a8cd85d 100644
> > --- a/xen/arch/x86/guest/hyperv/hyperv.c
> > +++ b/xen/arch/x86/guest/hyperv/hyperv.c
> > @@ -29,6 +29,7 @@ struct ms_hyperv_info __read_mostly ms_hyperv;
> >  void *hv_hypercall;
> >  static struct page_info *hv_hypercall_page;
> >  DEFINE_PER_CPU_READ_MOSTLY(struct hyperv_pcpu_page, hv_pcpu_input_arg);
> > +DEFINE_PER_CPU_READ_MOSTLY(unsigned int, hv_vp_index);
> >
> >  static const struct hypervisor_ops ops;
> >  const struct hypervisor_ops *__init hyperv_probe(void)
> > @@ -115,15 +116,26 @@ static void setup_hypercall_pcpu_arg(void)
> >      this_cpu(hv_pcpu_input_arg).mapping = mapping;
> >  }
> >
> > +static void setup_vp_index(void)
> > +{
> > +    uint64_t vp_index_msr;
> > +
> > +    rdmsrl(HV_X64_MSR_VP_INDEX, vp_index_msr);
> > +
> > +    this_cpu(hv_vp_index) = vp_index_msr;
> > +}
> 
> Is it worth a separate function vs. bundling this into
> setup_hypercall_pcpu_arg()?

My thinking is this may be called in the resume path; while
setup_hypercall_pcpu_arg doesn't (because they just set aside a bunch of
guest pages).

That is just a precaution. I haven't found any text in TLFS that vp
index will / can change after resume. This function can certainly be
folded into the other if that's preferred.

Wei.

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