Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752911AbbHMNqZ (ORCPT ); Thu, 13 Aug 2015 09:46:25 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56760 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752866AbbHMNqW (ORCPT ); Thu, 13 Aug 2015 09:46:22 -0400 From: =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= To: linux-kernel@vger.kernel.org Cc: kvm@vger.kernel.org, Paolo Bonzini , Steve Rutherford , stable@vger.kernel.org Subject: [PATCH 2/2] KVM: x86: fix edge EOI and IOAPIC reconfig race Date: Thu, 13 Aug 2015 15:46:10 +0200 Message-Id: <1439473570-13763-3-git-send-email-rkrcmar@redhat.com> In-Reply-To: <1439473570-13763-1-git-send-email-rkrcmar@redhat.com> References: <1439473570-13763-1-git-send-email-rkrcmar@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3158 Lines: 75 (The main problem is that we care about EOI of edge interrupts, but our house of cards started a long time ago, so overturning that decision is not ideal for a stable fix.) KVM uses eoi_exit_bitmap to track vectors that need an action on EOI. The problem is that IOAPIC can be reconfigured while an interrupt with old configuration is pending and eoi_exit_bitmap only remembers the newest configuration so EOI from the pending interrupt is not recognized. This is not a problem for level interrupts, because IOAPIC sends interrupt with the new configuration. And then there are edge interrupts with ACK notifiers, like i8254 timer; things can happen in this order 1) IOAPIC inject a vector from i8254 2) guest reconfigures that vector's VCPU and therefore eoi_exit_bitmap on original VCPU gets cleared 3) guest's handler for the vector does EOI 4) KVM's EOI handler doesn't pass that vector to IOAPIC because it is not in that VCPU's eoi_exit_bitmap 5) i8254 stops working A simple solution is to set the IOAPIC vector in eoi_exit_bitmap if the vector is in PIR/IRR/ISR. This creates an unwanted situation if the vector is reused by a non-IOAPIC source, but I think it is so rare that we don't want to make the solution more sophisticated. The simple solution also doesn't work if we are reconfiguring the vector. (Shouldn't happen in the wild and I'd rather fix users of ACK notifiers instead of working around that.) The are no races because ioapic injection and reconfig are locked. Fixes: 638e7c03efea ("KVM: x86: Add EOI exit bitmap inference") [Before 638e7c03efea, this bug happened only with APICv.] Fixes: c7c9c56ca26f ("x86, apicv: add virtual interrupt delivery support") Cc: Signed-off-by: Radim Krčmář --- arch/x86/kvm/ioapic.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/ioapic.c b/arch/x86/kvm/ioapic.c index 2dcda0f188ba..85d25fe25e39 100644 --- a/arch/x86/kvm/ioapic.c +++ b/arch/x86/kvm/ioapic.c @@ -239,6 +239,9 @@ void kvm_ioapic_scan_entry(struct kvm_vcpu *vcpu, u64 *eoi_exit_bitmap) union kvm_ioapic_redirect_entry *e; int index; + if (kvm_x86_ops->sync_pir_to_irr(vcpu)) + kvm_make_request(KVM_REQ_EVENT, vcpu); + spin_lock(&ioapic->lock); for (index = 0; index < IOAPIC_NUM_PINS; index++) { e = &ioapic->redirtbl[index]; @@ -246,7 +249,9 @@ void kvm_ioapic_scan_entry(struct kvm_vcpu *vcpu, u64 *eoi_exit_bitmap) kvm_irq_has_notifier(ioapic->kvm, KVM_IRQCHIP_IOAPIC, index) || index == RTC_GSI) { if (kvm_apic_match_dest(vcpu, NULL, 0, - e->fields.dest_id, e->fields.dest_mode)) + e->fields.dest_id, e->fields.dest_mode) || + (e->fields.trig_mode == IOAPIC_EDGE_TRIG && + kvm_apic_pending_eoi(vcpu, e->fields.vector))) __set_bit(e->fields.vector, (unsigned long *)eoi_exit_bitmap); } -- 2.5.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/