[PATCH 00/10] arm/arm64: KVM: Active interrupt state switching for shared devices

Eric Auger eric.auger at linaro.org
Wed Jun 10 04:13:37 PDT 2015

Hi Marc,
On 06/10/2015 11:03 AM, Marc Zyngier wrote:
> Hi Eric,
> On 10/06/15 09:33, Eric Auger wrote:
>> Hi Marc,
>> On 06/08/2015 07:03 PM, Marc Zyngier wrote:
>>> From day 1, our timer code has been using a terrible hack: whenever
>>> the guest is scheduled with a timer interrupt pending (i.e. the HW
>>> timer has expired), we restore the timer state with the MASK bit set,
>>> in order to avoid the physical interrupt to fire again. And again. And
>>> again...
>>> This is absolutely silly, for at least two reasons:
>>> - This relies on the device (the timer) having a mask bit that we can
>>>   play with. Not all devices are built like this.
>>> - This expects some behaviour of the guest that only works because the
>>>   both the kernel timer code and the KVM counterpart have been written
>>>   by the same idiot (the idiot being me).
>>> The One True Way is to set the GIC active bit when injecting the
>>> interrupt, and to context-switch across the world switch. This is what
>>> this series implements.
>>> We introduce a relatively simple infrastructure enabling the mapping
>>> of a virtual interrupt with its physical counterpart:
>>> - Whenever an virtual interrupt is injected, we look it up in an
>>>   rbtree. If we have a match, the interrupt is injected with the HW
>>>   bit set in the LR, together with the physical interrupt.
>>> - Across the world switch, we save/restore the active state for these
>>>   interrupts using the irqchip_state API.
>>> - On guest EOI, the HW interrupt is automagically deactivated by the
>>>   GIC, allowing the interrupt to be resampled.
>> I am lost about the status of the irqchip part, allowing EOImode=1 and
>> only dropping the prio for physical forwarded IRQs:
>> http://lkml.iu.edu/hypermail/linux/kernel/1410.3/00913.html
>> Doesn't this series also depend on those patches or did I miss something
>> on the ML?
> No, these patches are self-contained. As long as we only deal with
> shared devices, we don't need EOImode=1, as as we save/restore the
> active state, and the only irqchip change required (the state accessors)
> went in with the 4.1 merge window.
> The EOImode=1 stuff is still on the cards, and this series contains the
> basic infrastructure for that (the last patch in the series is there
> only for that purpose).
> Hope this helps,

OK thanks. I am currently rebasing my kvm-vfio series on yours. I will
let you know the outcome.

Best Regards

> 	M.

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