From 1f80ba3d201e55ec204f93af372d09412ab42d76 Mon Sep 17 00:00:00 2001 From: Paul Mackerras Date: Mon, 29 Apr 2019 15:42:36 +1000 Subject: [PATCH] KVM: PPC: Book3S HV: Fix XICS-on-XIVE H_IPI when priority = 0 This fixes a bug in the XICS emulation on POWER9 machines which is triggered by the guest doing a H_IPI with priority = 0 (the highest priority). What happens is that the notification interrupt arrives at the destination at priority zero. The loop in scan_interrupts() sees that a priority 0 interrupt is pending, but because xc->mfrr is zero, we break out of the loop before taking the notification interrupt out of the queue and EOI-ing it. (This doesn't happen when xc->mfrr != 0; in that case we process the priority-0 notification interrupt on the first iteration of the loop, and then break out of a subsequent iteration of the loop with hirq == XICS_IPI.) To fix this, we move the prio >= xc->mfrr check down to near the end of the loop. However, there are then some other things that need to be adjusted. Since we are potentially handling the notification interrupt and also delivering an IPI to the guest in the same loop iteration, we need to update pending and handle any q->pending_count value before the xc->mfrr check, rather than at the end of the loop. Also, we need to update the queue pointers when we have processed and EOI-ed the notification interrupt, since we may not do it later. Signed-off-by: Paul Mackerras --- arch/powerpc/kvm/book3s_xive_template.c | 78 +++++++++++++------------ 1 file changed, 40 insertions(+), 38 deletions(-) diff --git a/arch/powerpc/kvm/book3s_xive_template.c b/arch/powerpc/kvm/book3s_xive_template.c index 033363d6e764..0737acfd17f1 100644 --- a/arch/powerpc/kvm/book3s_xive_template.c +++ b/arch/powerpc/kvm/book3s_xive_template.c @@ -130,24 +130,14 @@ static u32 GLUE(X_PFX,scan_interrupts)(struct kvmppc_xive_vcpu *xc, */ prio = ffs(pending) - 1; - /* - * If the most favoured prio we found pending is less - * favored (or equal) than a pending IPI, we return - * the IPI instead. - * - * Note: If pending was 0 and mfrr is 0xff, we will - * not spurriously take an IPI because mfrr cannot - * then be smaller than cppr. - */ - if (prio >= xc->mfrr && xc->mfrr < xc->cppr) { - prio = xc->mfrr; - hirq = XICS_IPI; - break; - } - /* Don't scan past the guest cppr */ - if (prio >= xc->cppr || prio > 7) + if (prio >= xc->cppr || prio > 7) { + if (xc->mfrr < xc->cppr) { + prio = xc->mfrr; + hirq = XICS_IPI; + } break; + } /* Grab queue and pointers */ q = &xc->queues[prio]; @@ -184,9 +174,12 @@ skip_ipi: * been set and another occurrence of the IPI will trigger. */ if (hirq == XICS_IPI || (prio == 0 && !qpage)) { - if (scan_type == scan_fetch) + if (scan_type == scan_fetch) { GLUE(X_PFX,source_eoi)(xc->vp_ipi, &xc->vp_ipi_data); + q->idx = idx; + q->toggle = toggle; + } /* Loop back on same queue with updated idx/toggle */ #ifdef XIVE_RUNTIME_CHECKS WARN_ON(hirq && hirq != XICS_IPI); @@ -199,32 +192,41 @@ skip_ipi: if (hirq == XICS_DUMMY) goto skip_ipi; - /* If fetching, update queue pointers */ - if (scan_type == scan_fetch) { - q->idx = idx; - q->toggle = toggle; - } - - /* Something found, stop searching */ - if (hirq) - break; - - /* Clear the pending bit on the now empty queue */ - pending &= ~(1 << prio); + /* Clear the pending bit if the queue is now empty */ + if (!hirq) { + pending &= ~(1 << prio); - /* - * Check if the queue count needs adjusting due to - * interrupts being moved away. - */ - if (atomic_read(&q->pending_count)) { - int p = atomic_xchg(&q->pending_count, 0); - if (p) { + /* + * Check if the queue count needs adjusting due to + * interrupts being moved away. + */ + if (atomic_read(&q->pending_count)) { + int p = atomic_xchg(&q->pending_count, 0); + if (p) { #ifdef XIVE_RUNTIME_CHECKS - WARN_ON(p > atomic_read(&q->count)); + WARN_ON(p > atomic_read(&q->count)); #endif - atomic_sub(p, &q->count); + atomic_sub(p, &q->count); + } } } + + /* + * If the most favoured prio we found pending is less + * favored (or equal) than a pending IPI, we return + * the IPI instead. + */ + if (prio >= xc->mfrr && xc->mfrr < xc->cppr) { + prio = xc->mfrr; + hirq = XICS_IPI; + break; + } + + /* If fetching, update queue pointers */ + if (scan_type == scan_fetch) { + q->idx = idx; + q->toggle = toggle; + } } /* If we are just taking a "peek", do nothing else */ -- 2.30.2