On Tue, 2010-11-09 at 16:59 -0800, Tom Lyon wrote: > Alex - I am rejecting these 2 patches. > > For patch 1/2, I started with yours and found a couple of problems, but then I > got into the spirit and did a buinch more cleaning up. My patch to follow. Great, I'll take a look. > For patch 2/2, the INTX stuff, I don't really see the problem. If the user > turns on the bit, it'll result in at most one more interrupt, right? If he > turns off the bit, then he doesn't want interrupts. The scenario I'm thinking of is that an interrupt comes in, VFIO sets INTX_DISABLE, signals eventfd. We're already in a little bit of a weird state for a VM because INTX_DISABLE just changed on it's own. The guest interrupt handler blindly sets INTX_DISABLE again, and services the interrupt. This has the side effect of sending the emulated APIC EOI, which ends with VFIO clearing INTX_DISABLE, and now the guest is getting interrupts it's not expecting. Another aspect of it is that since the non-PCI-2.3/EOI patches, the VFIO interrupt handler is wrapped around an irq_disabled check, where irq_disabled only gets cleared by the EOI interfaces. So userspace might clear INTX_DISABLE and expect new INTx eventfds, but it won't happen without an EOI call. If we virtualize INTX_DISABLE, we can allow userspace to use either the EOI interfaces or (in)directly manipulate INTX_DISABLE from config space. I could also virtualize the INTX_DISABLE bit in the qemu VFIO driver but it gets a little bit tricky that I need to disable the EOI_EVENTFD to be sure to catch all the EOIs in userspace. Emulating INTX_DISABLE for non-PCI 2.3 devices is also a little more cumbersome from userspace, but ultimately I'm not sure how valuable that is anyway. Overall, I figured the above behavior issues were probably sufficient to implement it for everyone in the VFIO driver. Alex -- 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
