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Re: [Qemu-devel] [PATCH 2/4] q35: set split kernel irqchip as default
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH 2/4] q35: set split kernel irqchip as default |
Date: |
Wed, 19 Dec 2018 22:45:40 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.1 |
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
[Qemu-devel] [PATCH 3/4] x86-iommu: switch intr_supported to OnOffAuto type, Peter Xu, 2018/12/19
[Qemu-devel] [PATCH 4/4] x86-iommu: turn on IR by default if proper, Peter Xu, 2018/12/19