Re: [Xen-devel] [PATCH v2 4/4] x86/nvmx: update exit bitmap when using virtual interrupt delivery

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Sent: Thursday, March 26, 2020 5:22 PM
> 
> On Thu, Mar 26, 2020 at 03:17:59AM +0000, Tian, Kevin wrote:
> > > From: Roger Pau Monne <roger.pau@xxxxxxxxxx>
> > > Sent: Wednesday, March 25, 2020 6:19 PM
> > >
> > > Force an update of the EOI exit bitmap in nvmx_update_apicv, because
> > > the one performed in vmx_intr_assist might not be reached if the
> > > interrupt is intercepted by nvmx_intr_intercept returning true.
> > >
> > > Extract the code to update the exit bitmap from vmx_intr_assist into a
> > > helper and use it in nvmx_update_apicv.
> > >
> > > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > > ---
> > > Changes since v1:
> > >  - Reword commit message.
> > > ---
> > >  xen/arch/x86/hvm/vmx/intr.c       | 21 +++++++++++++--------
> > >  xen/arch/x86/hvm/vmx/vvmx.c       |  2 ++
> > >  xen/include/asm-x86/hvm/vmx/vmx.h |  2 ++
> > >  3 files changed, 17 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/xen/arch/x86/hvm/vmx/intr.c b/xen/arch/x86/hvm/vmx/intr.c
> > > index 49a1295f09..000e14af49 100644
> > > --- a/xen/arch/x86/hvm/vmx/intr.c
> > > +++ b/xen/arch/x86/hvm/vmx/intr.c
> > > @@ -224,6 +224,18 @@ static int nvmx_intr_intercept(struct vcpu *v,
> struct
> > > hvm_intack intack)
> > >      return 0;
> > >  }
> > >
> > > +void vmx_sync_exit_bitmap(struct vcpu *v)
> > > +{
> > > +    const unsigned int n = ARRAY_SIZE(v->arch.hvm.vmx.eoi_exit_bitmap);
> > > +    unsigned int i;
> > > +
> > > +    while ( (i = find_first_bit(&v->arch.hvm.vmx.eoi_exitmap_changed, n))
> <
> > > n )
> > > +    {
> > > +        clear_bit(i, &v->arch.hvm.vmx.eoi_exitmap_changed);
> > > +        __vmwrite(EOI_EXIT_BITMAP(i), v-
> >arch.hvm.vmx.eoi_exit_bitmap[i]);
> > > +    }
> > > +}
> > > +
> > >  void vmx_intr_assist(void)
> > >  {
> > >      struct hvm_intack intack;
> > > @@ -318,7 +330,6 @@ void vmx_intr_assist(void)
> > >                intack.source != hvm_intsrc_vector )
> > >      {
> > >          unsigned long status;
> > > -        unsigned int i, n;
> > >
> > >         /*
> > >          * intack.vector is the highest priority vector. So we set
> eoi_exit_bitmap
> > > @@ -379,13 +390,7 @@ void vmx_intr_assist(void)
> > >                      intack.vector;
> > >          __vmwrite(GUEST_INTR_STATUS, status);
> > >
> > > -        n = ARRAY_SIZE(v->arch.hvm.vmx.eoi_exit_bitmap);
> > > -        while ( (i = find_first_bit(&v->arch.hvm.vmx.eoi_exitmap_changed,
> > > -                                    n)) < n )
> > > -        {
> > > -            clear_bit(i, &v->arch.hvm.vmx.eoi_exitmap_changed);
> > > -            __vmwrite(EOI_EXIT_BITMAP(i), v-
> >arch.hvm.vmx.eoi_exit_bitmap[i]);
> > > -        }
> > > +        vmx_sync_exit_bitmap(v);
> > >
> > >          pt_intr_post(v, intack);
> > >      }
> > > diff --git a/xen/arch/x86/hvm/vmx/vvmx.c
> b/xen/arch/x86/hvm/vmx/vvmx.c
> > > index 8431c912a1..845dd87f75 100644
> > > --- a/xen/arch/x86/hvm/vmx/vvmx.c
> > > +++ b/xen/arch/x86/hvm/vmx/vvmx.c
> > > @@ -1418,6 +1418,8 @@ static void nvmx_update_apicv(struct vcpu *v)
> > >          status |= rvi & VMX_GUEST_INTR_STATUS_SUBFIELD_BITMASK;
> > >          __vmwrite(GUEST_INTR_STATUS, status);
> > >      }
> > > +
> > > +    vmx_sync_exit_bitmap(v);
> >
> > Similarly, I'd like to do the sync within the conditional block, when intr
> > status is actually changed. Otherwise, it becomes checking bitmap change
> > in every vmentry when apicv is enabled.
> 
> No - it will only check the bitmap when there's a virtual vmexit
> (which is where nvmx_update_apicv gets called), not on every vmentry.

you are right. I overlooked it. but still it's unnecessary to do it for
every virtual vmexit. 😊

> I can try to do this conditionally on whether GUEST_INTR_STATUS is
> actually changed.
> 

yes.

Thanks
Kevin