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

[Gleb Natapov <gleb@redhat.com>]

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.

--
			Gleb.