2014-03-21 10:28+0100, Paolo Bonzini:
> We will reuse it to process a nonzero IRR that is passed to KVM_SET_IRQCHIP.
>
> Reviewed-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> v1->v2:
> more comments
> change argument name from level to irq_level
>
> virt/kvm/ioapic.c | 74 +++++++++++++++++++++++++++++++++++++------------------
> 1 file changed, 50 insertions(+), 24 deletions(-)
>
> diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
> index 25e16a6898ed..270f7fe73f39 100644
> --- a/virt/kvm/ioapic.c
> +++ b/virt/kvm/ioapic.c
> @@ -163,6 +163,55 @@ static bool rtc_irq_check_coalesced(struct kvm_ioapic *ioapic)
> return false;
> }
>
> +static int ioapic_set_irq(struct kvm_ioapic *ioapic, unsigned int irq,
> + int irq_level, bool line_status)
> +{
> + union kvm_ioapic_redirect_entry entry;
> + u32 mask = 1 << irq;
> + u32 old_irr;
> + int edge, ret;
> +
> + entry = ioapic->redirtbl[irq];
> + edge = (entry.fields.trig_mode == IOAPIC_EDGE_TRIG);
> +
> + if (!irq_level) {
> + ioapic->irr &= ~mask;
> + ret = 1;
> + goto out;
> + }
> +
> + /*
> + * Return 0 for coalesced interrupts; for edge-triggered interrupts,
> + * this only happens if a previous edge has not been delivered due
> + * do masking. For level interrupts, the remote_irr field tells
(^ to)
> + * us if the interrupt is waiting for an EOI.
How do we know we haven't delivered an edge-triggered interrupt when
ioapic_service() always clears this IRR bit?
> + *
> + * RTC is special: it is edge-triggered, but userspace likes to know
> + * if it has been already ack-ed via EOI because coalesced RTC
> + * interrupts lead to time drift in Windows guests. So we track
> + * EOI manually for the RTC interrupt.
> + */
The comment makes me think we should not be coalescing more, but we do.
> + if (irq == RTC_GSI && line_status &&
> + rtc_irq_check_coalesced(ioapic)) {
> + ret = 0;
> + goto out;
> + }
> +
> + old_irr = ioapic->irr;
> + ioapic->irr |= mask;
> + if ((edge && old_irr == ioapic->irr) ||
> + (!edge && entry.fields.remote_irr)) {
(Fun fact: GCC 4.8.2 doesn't optimize it as well as
edge ? old_irr == ioapic->irr : entry.fields.remote_irr)
> + ret = 0;
> + goto out;
> + }
> +
> + ret = ioapic_service(ioapic, irq, line_status);
> +
> +out:
> + trace_kvm_ioapic_set_irq(entry.bits, irq, ret == 0);
> + return ret;
> +}
> +
> static void update_handled_vectors(struct kvm_ioapic *ioapic)
> {
> DECLARE_BITMAP(handled_vectors, 256);
> @@ -308,38 +357,15 @@ static int ioapic_service(struct kvm_ioapic *ioapic, int irq, bool line_status)
> int kvm_ioapic_set_irq(struct kvm_ioapic *ioapic, int irq, int irq_source_id,
> int level, bool line_status)
> {
> - u32 old_irr;
> - u32 mask = 1 << irq;
> - union kvm_ioapic_redirect_entry entry;
> int ret, irq_level;
>
> BUG_ON(irq < 0 || irq >= IOAPIC_NUM_PINS);
>
> spin_lock(&ioapic->lock);
> - old_irr = ioapic->irr;
> irq_level = __kvm_irq_line_state(&ioapic->irq_states[irq],
> irq_source_id, level);
> - entry = ioapic->redirtbl[irq];
> - if (!irq_level) {
> - ioapic->irr &= ~mask;
> - ret = 1;
> - } else {
> - int edge = (entry.fields.trig_mode == IOAPIC_EDGE_TRIG);
> + ret = ioapic_set_irq(ioapic, irq, irq_level, line_status);
>
> - if (irq == RTC_GSI && line_status &&
> - rtc_irq_check_coalesced(ioapic)) {
> - ret = 0; /* coalesced */
> - goto out;
> - }
> - ioapic->irr |= mask;
> - if ((edge && old_irr != ioapic->irr) ||
> - (!edge && !entry.fields.remote_irr))
> - ret = ioapic_service(ioapic, irq, line_status);
> - else
> - ret = 0; /* report coalesced interrupt */
> - }
> -out:
> - trace_kvm_ioapic_set_irq(entry.bits, irq, ret == 0);
> spin_unlock(&ioapic->lock);
>
> return ret;
> --
> 1.8.3.1
>
>
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