From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:55151) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1To6Ji-0003bx-Sr for qemu-devel@nongnu.org; Thu, 27 Dec 2012 00:47:46 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1To6Jf-0003t0-UO for qemu-devel@nongnu.org; Thu, 27 Dec 2012 00:47:42 -0500 Received: from qmta01.emeryville.ca.mail.comcast.net ([2001:558:fe2d:43:76:96:30:16]:46009) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1To6Jf-0003sv-Lz for qemu-devel@nongnu.org; Thu, 27 Dec 2012 00:47:39 -0500 From: Matthew Ogilvie Date: Wed, 26 Dec 2012 22:39:55 -0700 Message-Id: <1356586796-7631-4-git-send-email-mmogilvi_qemu@miniinfo.net> In-Reply-To: <1356586796-7631-1-git-send-email-mmogilvi_qemu@miniinfo.net> References: <1356586796-7631-1-git-send-email-mmogilvi_qemu@miniinfo.net> Subject: [Qemu-devel] [PATCH KVM v2 3/4] KVM: fix i8259 interrupt high to low transition logic List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Gleb Natapov , Jan Kiszka , Matthew Ogilvie , kvm@vger.kernel.org, "Maciej W. Rozycki" Intel's definition of "edge triggered" means: "asserted with a low-to-high transition at the time an interrupt is registered and then kept high until the interrupt is served via one of the EOI mechanisms or goes away unhandled." So the only difference between edge triggered and level triggered is in the leading edge, with no difference in the trailing edge. This bug manifested itself when the guest was Microport UNIX System V/386 v2.1 (ca. 1987), because it would sometimes mask off IRQ14 in the slave IMR after it had already been asserted. The master would still try to deliver an interrupt to the CPU even though IRQ2 had dropped again, resulting in a spurious interupt (IRQ15) and a panicked UNIX kernel. Signed-off-by: Matthew Ogilvie --- arch/x86/kvm/i8259.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) diff --git a/arch/x86/kvm/i8259.c b/arch/x86/kvm/i8259.c index cc31f7c..76d8dc1 100644 --- a/arch/x86/kvm/i8259.c +++ b/arch/x86/kvm/i8259.c @@ -111,8 +111,10 @@ static inline int pic_set_irq1(struct kvm_kpic_state *s, int irq, int level) s->irr |= mask; } s->last_irr |= mask; - } else + } else { + s->irr &= ~mask; s->last_irr &= ~mask; + } return (s->imr & mask) ? -1 : ret; } @@ -169,14 +171,10 @@ static void pic_update_irq(struct kvm_pic *s) { int irq2, irq; + /* slave PIC notifies master PIC via IRQ2 */ irq2 = pic_get_irq(&s->pics[1]); - if (irq2 >= 0) { - /* - * if irq request by slave pic, signal master PIC - */ - pic_set_irq1(&s->pics[0], 2, 1); - pic_set_irq1(&s->pics[0], 2, 0); - } + pic_set_irq1(&s->pics[0], 2, irq2 >= 0); + irq = pic_get_irq(&s->pics[0]); pic_irq_request(s->kvm, irq >= 0); } -- 1.7.10.2.484.gcd07cc5