On Wed, Dec 26, 2012 at 10:39:52PM -0700, Matthew Ogilvie wrote: > Changes since version 1 (from Sep 9): > * Split off patch 1; this is the critical prerequisite to > make the i8254 work with the fixed i8259. > * Add patch 2, to make additional changes to the i8254 > to make it consistent with the spec and with proposed changes > to qemu's i8254 model. > > Background: > > According to the spec, the i8259 will cancel an interrupt if > the line goes low before it starts servicing it, even when > it is considered edge-triggered. This is a problem > with an old Microport UNIX guest (ca 1987), where the > guest masks off IRQ14 in the slave i8259, but the host's > master i8259 model will still try to deliver an interrupt even after > IRQ2 has been brought low, resulting in a spurious interrupt (IRQ15). > > Before the i8259 can be fixed, the i8254 model needs to be fixed > so it doesn't depend on the broken i8259. > > Alternative: This could be narrowly fixed for IRQ2 only with no > risk at all (and no need to touch the i8254), but if possible it > seems reasonable to fix it for all lines at the same time. > > But there may be some risk: > > First, I think I've convinced myself that between the i8254 and i8259, > the only substantial migration breakage should be when a > whole series of conditions are met, and the combination > should be rare enough not to worry about it. See writeup > in my qemu patch series (version 8; Dec 16). > > Second, there is also the possibility that other devices are relying > on the broken model. I'm especially concerned with various users > of a function called > > qemu_irq_pulse() > > in the qemu source tree, which immediately lowers IRQ line after > raising it. If any of those calls are routed straight into > the i8259 (as opposed to an APIC or some other chip), then it > probably won't behave as desired. > > I'll probably dig into qemu_irq_pulse() callers more carefully > eventually, but there are lot of them, and any high-level incite > anyone can provide into them would be helpful. > $ git grep qemu_irq_pulse | wc -l 34 Files are: hw/bonito.c hw/dma.c hw/grlib_apbuart.c hw/grlib_gptimer.c hw/hpet.c hw/irq.h hw/milkymist-ac97.c hw/milkymist-minimac2.c hw/milkymist-pfpu.c hw/milkymist-softusb.c hw/milkymist-sysctl.c hw/milkymist-tmu2.c hw/omap1.c hw/omap_gptimer.c hw/onenand.c hw/spapr_events.c hw/spapr_llan.c hw/spapr_pci.c hw/spapr_vio.c hw/spapr_vty.c hw/stellaris.c hw/xilinx_ethlite.c Looks like only two of those are relevant to PC platform hw/dma.c and hw/hpet.c. In hw/dma.c it is used for internal qemu communication, not real device. In hw/hpet.c from a quick glance it looks like _pulse is only used when HPET in not in legacy emulation mode which means that pulse should be directed to APIC. > See the Dec 16 patch series I sent to the qemu mailing list for > more information. > http://search.gmane.org/?query=ogilvie&group=gmane.comp.emulators.qemu > > Matthew Ogilvie (4): > KVM: fix i8254 IRQ0 to be normally high > KVM: additional i8254 output fixes > KVM: fix i8259 interrupt high to low transition logic > KVM: i8259: refactor pic_set_irq level logic > > arch/x86/kvm/i8254.c | 50 +++++++++++++++++++++++++++++++++++++++----------- > arch/x86/kvm/i8259.c | 36 ++++++++++++++---------------------- > 2 files changed, 53 insertions(+), 33 deletions(-) > > -- > 1.7.10.2.484.gcd07cc5 -- Gleb. -- 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
