On 12/02/2018 12:30, Vitaly Kuznetsov wrote: >> - Radim's suggestion was to disable DIRECTED_EOI unconditionally but I'm not >> that radical :-) In theory, we may have multiple IOAPICs in userspace in >> future and DIRECTED_EOI can be leveraged. > > I sort of agree on this, especially considering that we already have > IOAPIC version 0x20 support in QEMU already. Yeah, and directed EOI is faster AFAIU. > My thoughts were: with in-kernel IOAPIC nobody does EOI broadcast > disabling today or he's already broken -- there's no way to EOI > level-triggered interrupts. And the patch changes nothing for QEMU > ioapic implementation. > > What I'm not sure about is if we allow migration between in-kernel and > QEMU ioapic implementations. I don't think so but in case we do it is > again already broken because going down from 0x20 to 0x11 will leave you > without EOI register. Migrating from 0x11 to 0x20 should be fine, the > guest will continue without knowing there's a new feature available. No, we don't allow that. Paolo
