On Thu, Mar 26, 2020 at 03:13:56AM +0000, Tian, Kevin wrote:
> > From: Roger Pau Monne <roger....@citrix.com>
> > Sent: Wednesday, March 25, 2020 6:19 PM
> >
> > Updating SVI is required when an interrupt has been injected using the
> > Ack on exit VMEXIT feature, so that the in service interrupt in the
> > GUEST_INTR_STATUS matches the vector that is signaled in
> > VM_EXIT_INTR_INFO.
> >
> > Updating RVI however is not tied to the Ack on exit feature, as it
> > signals the next vector to be injected, and hence should always be
> > updated to the next pending vector, regardless of whether Ack on exit
> > is enabled.
> >
> > Signed-off-by: Roger Pau Monné <roger....@citrix.com>
> > ---
> > xen/arch/x86/hvm/vmx/vvmx.c | 22 +++++++++++++++++-----
> > 1 file changed, 17 insertions(+), 5 deletions(-)
> >
> > diff --git a/xen/arch/x86/hvm/vmx/vvmx.c b/xen/arch/x86/hvm/vmx/vvmx.c
> > index 1753005c91..8431c912a1 100644
> > --- a/xen/arch/x86/hvm/vmx/vvmx.c
> > +++ b/xen/arch/x86/hvm/vmx/vvmx.c
> > @@ -1384,26 +1384,38 @@ static void nvmx_update_apicv(struct vcpu *v)
> > struct nestedvmx *nvmx = &vcpu_2_nvmx(v);
> > unsigned long reason = get_vvmcs(v, VM_EXIT_REASON);
> > unsigned long intr_info = get_vvmcs(v, VM_EXIT_INTR_INFO);
> > + int rvi;
> >
> > if ( reason == EXIT_REASON_EXTERNAL_INTERRUPT &&
> > nvmx->intr.source == hvm_intsrc_lapic &&
> > (intr_info & INTR_INFO_VALID_MASK) )
> > {
> > uint16_t status;
> > - uint32_t rvi, ppr;
> > - uint32_t vector = intr_info & 0xff;
> > + uint32_t ppr;
> > + unsigned int vector = intr_info & INTR_INFO_VECTOR_MASK;
> > struct vlapic *vlapic = vcpu_vlapic(v);
> >
> > + /*
> > + * Update SVI to record the currently in service interrupt that's
> > + * signaled in EXIT_INTR_INFO.
> > + */
> > vlapic_ack_pending_irq(v, vector, 1);
> >
> > ppr = vlapic_set_ppr(vlapic);
> > WARN_ON((ppr & 0xf0) != (vector & 0xf0));
> >
> > status = vector << VMX_GUEST_INTR_STATUS_SVI_OFFSET;
> > - rvi = vlapic_has_pending_irq(v);
> > - if ( rvi != -1 )
> > - status |= rvi & VMX_GUEST_INTR_STATUS_SUBFIELD_BITMASK;
> > + __vmwrite(GUEST_INTR_STATUS, status);
> > + }
> > +
> > + rvi = vlapic_has_pending_irq(v);
> > + if ( rvi != -1 )
> > + {
> > + unsigned long status;
> >
> > + __vmread(GUEST_INTR_STATUS, &status);
> > + status &= ~VMX_GUEST_INTR_STATUS_SUBFIELD_BITMASK;
> > + status |= rvi & VMX_GUEST_INTR_STATUS_SUBFIELD_BITMASK;
> > __vmwrite(GUEST_INTR_STATUS, status);
> > }
>
> I have two minor comments. First, original code requires only one
> __vmwrite but now needs two writes and one read for Ack-on-exit
> is set. Can we optimize to sustain the original behavior?
I think I can manage to do a single write by using a global status
variable initialized to 0 and only do the vmwrite if the value is != 0
by the end of the function.
> Second,
> although I didn't come up a case where always updating RVI (w/
> pending interrupt) may bring some bad effect, it is anyway safer
> to put the whole logic within the check of vmexit reason and intr
> source.
I also considered this and decided there was no harm in always
updating RVI if there's a pending interrupt, it could even prevent a
future VMEXIT to update RVI AFAICT?
If you prefer I can return early from the function if reason !=
EXIT_REASON_EXTERNAL_INTERRUPT.
Thanks, Roger.
