Am 03.11.2010 16:57, Alex Williamson wrote: > On Wed, 2010-11-03 at 10:43 +0200, Michael S. Tsirkin wrote: >> On Wed, Nov 03, 2010 at 09:11:16AM +0100, Jan Kiszka wrote: >>> From: Jan Kiszka <jan.kiszka@xxxxxxxxxxx> >>> >>> PCI 2.3 allows to generically disable IRQ sources at device level. This >>> enables us to share IRQs of such devices between on the host side when >>> passing them to a guest. This feature is optional, user space has to >>> request it explicitly. >>> >>> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx> >> >> >> I just realized something. >> With this patch, if guest ever looks at >> interrupt disable bit, it will go crazy as that bit goes on/off by >> itself. I guess we could have an ioctl to set/clear the bit on >> device, and have qemu call that on config write into command/status >> register. >> >> There's also something I don't completely unerstand with current code: >> how does interrupt sharing work? E.g. can assigned and emulated >> devices share an interrupt? > > I've been pondering this with VFIO too. There it seems to work, even > when I enable irqfd. The VFIO kernel/qemu driver needs to filter EOIs > based on whether the interrupt was actually asserted by the device, but > I think we're likely relying somewhat on interrupts being reasserted to > help us keep everything serviced. I don't think this filtering exists. The ack notifier that is fired on EOI matches the GSI, hitting anyone who is registered. I think the problem is that, while user space properly or's the input of all PCI devices on a IRQ line (e.g. in piix3_set_irq), kernel-side users apparently prefer to mess directly with the irqchip. Unless I'm missing something, that is long broken. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
