Re: [PATCH v4 5/7] KVM: Recalculate destination vcpu map

[Gleb Natapov <gleb@redhat.com>]

On Thu, Mar 21, 2013 at 07:02:39AM +0000, Zhang, Yang Z wrote:
> Gleb Natapov wrote on 2013-03-20:
> > On Wed, Mar 20, 2013 at 07:36:17PM +0800, Yang Zhang wrote:
> >> From: Yang Zhang <yang.z.zhang@Intel.com>
> >> 
> >> Update RTC interrrupt's destination vcpu map when ioapic entry of RTC
> >> or apic register (id, ldr, dfr) is changed.
> >> 
> >> Signed-off-by: Yang Zhang <yang.z.zhang@Intel.com>
> >> ---
> >>  virt/kvm/ioapic.c |    9 +++++++--
> >>  1 files changed, 7 insertions(+), 2 deletions(-)
> >> diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
> >> index ddf9414..91b4c08 100644
> >> --- a/virt/kvm/ioapic.c
> >> +++ b/virt/kvm/ioapic.c
> >> @@ -121,6 +121,7 @@ void kvm_ioapic_scan_entry(struct kvm_vcpu *vcpu,
> >>  { 	struct kvm_ioapic *ioapic = vcpu->kvm->arch.vioapic; 	union
> >>  kvm_ioapic_redirect_entry *e; +	unsigned long *rtc_map =
> >>  ioapic->rtc_status.vcpu_map; 	struct kvm_lapic_irq irqe; 	int index;
> >> @@ -130,15 +131,19 @@ void kvm_ioapic_scan_entry(struct kvm_vcpu *vcpu,
> >>  		if (!e->fields.mask &&
> >>  			(e->fields.trig_mode == IOAPIC_LEVEL_TRIG ||
> >>  			 kvm_irq_has_notifier(ioapic->kvm, KVM_IRQCHIP_IOAPIC,
> >> -				 index))) {
> >> +				 index) || index == 8)) {
> >>  			irqe.dest_id = e->fields.dest_id;
> >>  			irqe.vector = e->fields.vector;
> >>  			irqe.dest_mode = e->fields.dest_mode;
> >>  			irqe.shorthand = 0;
> >>  
> >>  			if (kvm_apic_match_dest(vcpu, NULL, irqe.shorthand,
> >> -						irqe.dest_id, irqe.dest_mode))
> >> +						irqe.dest_id, irqe.dest_mode)) {
> >>  				__set_bit(irqe.vector, eoi_exit_bitmap);
> >> +				if (index == 8)
> >> +					__set_bit(vcpu->vcpu_id, rtc_map);
> >> +			} else if (index == 8)
> >> +				__clear_bit(vcpu->vcpu_id, rtc_map);
> > rtc_map bitmap is accessed from different vcpus simultaneously so access
> > has to be atomic. We also have a race:
> > 
> > vcpu0                               iothread
> > ioapic config changes
> > request scan ioapic
> >                                      inject rtc interrupt
> >                                      use old vcpu mask
> > scan_ioapic()
> > recalculate vcpu mask
> > 
> > So this approach (suggested by me :() will not work.
> > 
> > Need to think about it some more. May be your idea of building a bitmap
> > while injecting the interrupt is the way to go indeed: pass a pointer to
> > a bitmap to kvm_irq_delivery_to_apic() and build it there. Pass NULL
> > pointer if caller does not need to track vcpus.
> How about build it in kvm_apic_set_irq()? It should be more straightforward.
> 
Sure, pass a pointer there. Just do not access ioapic directly.

--
			Gleb.