* A question about vtimer interrupt when guest_exit
[not found] <B99C36949BCC8541A564076B659DD970671E7965@nkgeml514-mbs.china.huawei.com>
@ 2017-04-13 7:32 ` Marc Zyngier
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From: Marc Zyngier @ 2017-04-13 7:32 UTC (permalink / raw)
To: linux-arm-kernel
On 13/04/17 07:14, Wangxuefeng (E) wrote:
>
>
> Hi Marc,
>
> I have a question about the vtimer ppi report when guest exit.
>
>
>
> 1. The flow: vtimer PPI assert->guest_exit->disable the
> vtimer->msr daifclear, #0x2
>
>
>
> 2. When disable the vtimer, the nCNTVIRQ will be cleared, then the
> clear request will be sent to GICD, GICD send clear request to GICC then
> clear the irq to CPU. So the clear request indeed be sent to CPU need
> some cycles(for example: N cycles),
>
> while the cpu execute from ?disable vtimer? to ?clear the mask of irq?
> need M cycles, how the software make sure the interrupt won?t be taken
> by CPU before it indeed get the clear request? Or the ARM architecture
> make sure M<N.
The architecture doesn't guarantee anything like that. If your GIC is
too slow to retire the pending interrupt by the time we unmask
interrupts at the CPU level, you'll get a (harmless) warning that we've
taken a spurious timer interrupt. This isn't a big deal, just the
indication that the HW is a bit imbalanced (fast CPU, slow GIC).
We may revise the way we handle the timer interrupt@some point,
taking the interrupt and keeping it active while injected into the guest.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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2017-04-13 7:32 ` A question about vtimer interrupt when guest_exit Marc Zyngier
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