@@ -323,8 +323,12 @@ EXPORT_SYMBOL_GPL(kvm_apic_update_irr);
static inline void apic_set_irr(int vec, struct kvm_lapic *apic)
{
- apic->irr_pending = true;
apic_set_vector(vec, apic->regs + APIC_IRR);
+ /*
+ * irr_pending must be true if any interrupt is pending; set it after
+ * APIC_IRR to avoid race with apic_clear_irr
+ */
+ apic->irr_pending = true;
}
static inline int apic_search_irr(struct kvm_lapic *apic)
@@ -356,13 +360,15 @@ static inline void apic_clear_irr(int vec, struct kvm_lapic *apic)
vcpu = apic->vcpu;
- apic_clear_vector(vec, apic->regs + APIC_IRR);
- if (unlikely(kvm_apic_vid_enabled(vcpu->kvm)))
+ if (unlikely(kvm_apic_vid_enabled(vcpu->kvm))) {
/* try to update RVI */
+ apic_clear_vector(vec, apic->regs + APIC_IRR);
kvm_make_request(KVM_REQ_EVENT, vcpu);
- else {
- vec = apic_search_irr(apic);
- apic->irr_pending = (vec != -1);
+ } else {
+ apic->irr_pending = false;
+ apic_clear_vector(vec, apic->regs + APIC_IRR);
+ if (apic_search_irr(apic) != -1)
+ apic->irr_pending = true;
}
}
This is a note to let you know that I have just added a patch titled KVM: x86: Fix lost interrupt on irr_pending race to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree which can be found at: http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue This patch is scheduled to be released in version 3.16.7-ckt11. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.16.y-ckt tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Luis ------ From 94cef1f52c31ff6d6b7b8bde0945cefaea055e8b Mon Sep 17 00:00:00 2001 From: Nadav Amit <namit@cs.technion.ac.il> Date: Sun, 16 Nov 2014 23:49:07 +0200 Subject: KVM: x86: Fix lost interrupt on irr_pending race commit f210f7572bedf3320599e8b2d8e8ec2d96270d0b upstream. apic_find_highest_irr assumes irr_pending is set if any vector in APIC_IRR is set. If this assumption is broken and apicv is disabled, the injection of interrupts may be deferred until another interrupt is delivered to the guest. Ultimately, if no other interrupt should be injected to that vCPU, the pending interrupt may be lost. commit 56cc2406d68c ("KVM: nVMX: fix "acknowledge interrupt on exit" when APICv is in use") changed the behavior of apic_clear_irr so irr_pending is cleared after setting APIC_IRR vector. After this commit, if apic_set_irr and apic_clear_irr run simultaneously, a race may occur, resulting in APIC_IRR vector set, and irr_pending cleared. In the following example, assume a single vector is set in IRR prior to calling apic_clear_irr: apic_set_irr apic_clear_irr ------------ -------------- apic->irr_pending = true; apic_clear_vector(...); vec = apic_search_irr(apic); // => vec == -1 apic_set_vector(...); apic->irr_pending = (vec != -1); // => apic->irr_pending == false Nonetheless, it appears the race might even occur prior to this commit: apic_set_irr apic_clear_irr ------------ -------------- apic->irr_pending = true; apic->irr_pending = false; apic_clear_vector(...); if (apic_search_irr(apic) != -1) apic->irr_pending = true; // => apic->irr_pending == false apic_set_vector(...); Fixing this issue by: 1. Restoring the previous behavior of apic_clear_irr: clear irr_pending, call apic_clear_vector, and then if APIC_IRR is non-zero, set irr_pending. 2. On apic_set_irr: first call apic_set_vector, then set irr_pending. Signed-off-by: Nadav Amit <namit@cs.technion.ac.il> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- arch/x86/kvm/lapic.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-)