On Thu, 8 Aug 2024 at 12:54, Daniel P. Berrangé <berra...@redhat.com> wrote: > > On Thu, Aug 08, 2024 at 12:32:35PM +0100, Peter Maydell wrote: > > On Thu, 8 Aug 2024 at 12:23, Daniel P. Berrangé <berra...@redhat.com> wrote: > > > On Thu, Aug 08, 2024 at 11:15:17AM +0100, Peter Maydell wrote: > > > > It's not possible to use KVM with that machine type, so the > > > > question is a bit moot. (This also indicates that the > > > > interface is not very helpful -- it purports to tell the > > > > management layer whether it can use an accelerated in-kernel > > > > GIC, but because it doesn't specifiy the board type there's > > > > no way to provide an accurate answer. It would be useful > > > > to know exactly what libvirt/etc actually use this for...) > > > > > > Libvirt uses this exclusively with the arm 'virt' machine type. > > > > > > If the user didn't express any GIC preference, then if KVM is in use, > > > we'll pick the highest GIC version QEMU reports as supported. > > > > You can get that without querying QEMU by asking for 'gic-version=max' > > if you like. > > This isn't in the VM startup path. It is when we expand the user > provided XML config into an ABI stable XML config by filling in > the blanks left by the user. So we need to actually query the > values available. > > > > If TCG > > > is in use we'll always pick v2, even if QEMU reports v3 is emulatable > > > due to the v3 impl lacking MSI controller which we need for PCI-e > > > > Our emulated GICv3 supports the ITS which has MSI support, so I'm not > > sure what forcing GICv2 is getting you here. Looking at the linked > > RHEL bugzilla bug, I suspect this is an out-of-date policy from before > > we added the ITS emulation in 2021 (it's present by default > > in virt-2.8 and later machine types). So that is something that > > libvirt should update I think. > > It looks like it is virt-6.2 or later, and libvirt can probe it > by looking for existence of the arm-gicv3-its QOM type IIUC.
Yes. (I was confused by the 'no_its' setting in virt-2.8, but that is for "is there a KVM ITS", and no_tcg_its is separate and as you say added with 6.2.) -- PMM
