From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53737) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YW15N-0002WW-Rw for qemu-devel@nongnu.org; Thu, 12 Mar 2015 07:15:31 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YW15H-00019h-Sm for qemu-devel@nongnu.org; Thu, 12 Mar 2015 07:15:29 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60131) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YW15H-00019Z-Jv for qemu-devel@nongnu.org; Thu, 12 Mar 2015 07:15:23 -0400 Date: Thu, 12 Mar 2015 12:15:18 +0100 From: "Michael S. Tsirkin" Message-ID: <20150312120624-mutt-send-email-mst@redhat.com> References: <1426142455-3739-1-git-send-email-famz@redhat.com> <20150312103850-mutt-send-email-mst@redhat.com> <20150312100028.GC15561@ad.nay.redhat.com> <20150312111125-mutt-send-email-mst@redhat.com> <20150312115534-mutt-send-email-mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Subject: Re: [Qemu-devel] [PATCH] virtio-pci: Clear IRQ at reset List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Maydell Cc: Fam Zheng , QEMU Developers On Thu, Mar 12, 2015 at 11:04:33AM +0000, Peter Maydell wrote: > On 12 March 2015 at 10:57, Michael S. Tsirkin wrote: > > This isn't a device reset though. > > The function that Fam is touching is called > > when a special "virtio reset" register to > > poked by the driver. > > It only resets part of the device, not all of it, > > and it seems reasonable to ask that it clear the > > interrupt. > > Oh, right, sorry. Yes, that should clear the interrupt, then. > (Is there a similar bug on other virtio transports?) > > -- PMM Hmm interesting. I looked at virtio_reset and that one does: vdev->isr = 0; vdev->config_vector = VIRTIO_NO_VECTOR; virtio_notify_vector(vdev, vdev->config_vector); which in turn would call static void virtio_pci_notify(DeviceState *d, uint16_t vector) { VirtIOPCIProxy *proxy = to_virtio_pci_proxy_fast(d); if (msix_enabled(&proxy->pci_dev)) msix_notify(&proxy->pci_dev, vector); else { VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus); pci_set_irq(&proxy->pci_dev, vdev->isr & 1); } } since isr is 0, and msi is disabled, it looks like pci_set_irq will get invoked automatically. so at this point I stopped understanding how can this patch help. Fam, does your patch actually help some guests? Could you pls investigate why isn't virtio_reset sufficient? -- MST