From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=41751 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OqhwY-0004w0-5E for qemu-devel@nongnu.org; Wed, 01 Sep 2010 03:41:14 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OqhwU-0005PE-1c for qemu-devel@nongnu.org; Wed, 01 Sep 2010 03:41:14 -0400 Received: from mx1.redhat.com ([209.132.183.28]:3980) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OqhwT-0005Ob-Qr for qemu-devel@nongnu.org; Wed, 01 Sep 2010 03:41:10 -0400 Message-ID: <4C7E038E.9050407@redhat.com> Date: Wed, 01 Sep 2010 10:41:02 +0300 From: Avi Kivity MIME-Version: 1.0 References: <1283249237-31881-1-git-send-email-agraf@suse.de> In-Reply-To: <1283249237-31881-1-git-send-email-agraf@suse.de> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: [Qemu-devel] Re: [RFC] KVM: PPC: Add level based interrupt logic List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexander Graf Cc: Marcelo Tosatti , qemu-devel List On 08/31/2010 01:07 PM, Alexander Graf wrote: > KVM on PowerPC used to have completely broken interrupt logic. Usually, > interrupts work by having a PIC that pulls a line up/down, so the CPU knows > that an interrupt is active. This line stays active until some action is > done to the PIC to release the line. > > On KVM for PPC, we just checked if there was an interrupt pending and pulled > a line in the kernel module. We never released it though, hoping that kernel > space would just declare an interrupt as released when injected - which is > wrong. > > To fix this, we need to completely redesign the interrupt injection logic. > Whenever an interrupt line gets triggered, we need to notify kernel space > that the line is up. Whenever it gets released, we do the same. This way > we can assure that the interrupt state is always known to kernel space. > > This fixes random stalls in KVM guests on PowerPC that were waiting for > an interrupt while everyone else thought they received it already. This is more or less equivalent to KVM_IRQ_LINE. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.