Re: [Qemu-devel] [PATCH v2] x86: ioapic: conditionally upgrade IOAPIC version

[Peter Xu <peterx@redhat.com>]

On Mon, Aug 01, 2016 at 12:38:58PM +0200, Paolo Bonzini wrote:
> 
> 
> On 26/07/2016 05:28, Peter Xu wrote:
> > IOMMU IR and IOAPIC legacy devices (e.g., e1000) cannot work well
> > together with some old Linux kernels (upstream before v4.0, or any
> > released RHEL kernels). This patch fixes it.
> > 
> > The problem is that: some old linux kernels (with IR enabled) only
> > support IOAPIC chips with version 0x20. New kernels after commit d32932d
> > ("x86/irq: Convert IOAPIC to use hierarchical irqdomain interfaces")
> > fixed this problem. To make sure we can work with even old kernels,
> > let's upgrade our IOAPIC to version 0x20.
> > 
> > To make sure we have minimum impact on old systems, IOAPIC version is
> > only boosted to 0x20 when vIOMMU IR is enabled. Besides that, the old
> > version 0x11 is used.
> 
> I'd rather do this conditional only on the machine type, but as you
> pointed out it's a bit late to change the default in QEMU 2.7.
> Therefore, for 2.7 you could add a property to the IOAPIC device, and
> document that you need "-global ioapic.version=0x20" for interrupt
> remapping to work with Linux <= 4.0.  QEMU 2.8 can then flip the default
> for the new machine types.

Yes, an property seems to be a better choice. V3 sent. Thanks!

-- peterx