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

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

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

Thanks, Roger.