Re: [Xen-devel] [PATCH 8/8] x86/hyperv: setup VP assist page

[Wei Liu <wl@xxxxxxx>]

On Sun, Dec 29, 2019 at 07:59:48PM +0000, Michael Kelley wrote:
> From: Wei Liu <wei.liu.xen@xxxxxxxxx> On Behalf Of Wei Liu  Sent: Sunday, 
> December 29, 2019 10:34 AM
> > 
> > VP assist page is rather important as we need to toggle some bits in
> > that page such that L1 guest can make hypercalls directly to L0 Hyper-V.
> > 
> > Preemptively split out set_vp_assist page which will be used in the resume
> > path.
> > 
> > Signed-off-by: Wei Liu <liuwe@xxxxxxxxxxxxx>
> > ---
> >  xen/arch/x86/guest/hyperv/hyperv.c | 35 ++++++++++++++++++++++++++++++
> >  xen/include/asm-x86/guest/hyperv.h |  1 +
> >  2 files changed, 36 insertions(+)
> > 
> > diff --git a/xen/arch/x86/guest/hyperv/hyperv.c 
> > b/xen/arch/x86/guest/hyperv/hyperv.c
> > index da3a8cd85d..a88b9ae6d9 100644
> > --- a/xen/arch/x86/guest/hyperv/hyperv.c
> > +++ b/xen/arch/x86/guest/hyperv/hyperv.c
> > @@ -30,6 +30,7 @@ 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);
> > +DEFINE_PER_CPU_READ_MOSTLY(struct hyperv_pcpu_page, hv_vp_assist);
> > 
> >  static const struct hypervisor_ops ops;
> >  const struct hypervisor_ops *__init hyperv_probe(void)
> > @@ -125,17 +126,51 @@ static void setup_vp_index(void)
> >      this_cpu(hv_vp_index) = vp_index_msr;
> >  }
> > 
> > +static void set_vp_assist(void)
> > +{
> > +    uint64_t val = paddr_to_pfn(this_cpu(hv_vp_assist).maddr);
> > +
> > +    val = (val << HV_X64_MSR_VP_ASSIST_PAGE_ADDRESS_SHIFT) | 
> 
> I'd recommend using HV_HYP_PAGE_SHIFT instead of
> HV_X64_MSR_VP_ASSIST_PAGE_ADDRESS_SHIFT.  On the Linux side,
> I'm planning to remove that #define and the similar
> *_PAGE_ADDRESS_MASK in favor of the newer HV_HYP_PAGE_* values.
> There's nothing special about the VP assist page, so using the generic
> #defines based on the Hyper-V page size is reasonable.

Ack.

Wei.

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