On 19/12/18 22:24, Eduardo Habkost wrote:
On Wed, Dec 19, 2018 at 09:12:55PM +0100, Paolo Bonzini wrote:
On 19/12/18 09:50, Peter Xu wrote:
Starting from QEMU 4.0, let's specify "split" as the default value for kernel-irqchip.
So for QEMU>=4.0 we'll have: allowed=Y,required=N,split=Y for QEMU<=3.1 we'll have: allowed=Y,required=N,split=N (omitting all the "kernel_irqchip_" prefix)
Note that this "split" is optional - we'll first try to enable split kernel irqchip, and we'll fall back to complete kernel irqchip if we found that the kernel capability is missing.
Please just fail completely and require a new kernel for the 4.0 machine type. There are subtle differences between kernel and QEMU irqchip, I don't think we want to open that can of worms.
This would make existing VMs that are runnable with pc-q35-3.1.0 not runnable by only updating the machine-type.
The good news is that we can make this a non-issue by clearly documenting that QEMU needs a more recent kernel (just like we'll do for RDTSCP[1]).
Right, RDTSCP is exactly what came to mind. Paolo