Re: [PATCH] arm: KVM: Don't return PSCI_INVAL if waitqueue is inactive

Peter Maydell
2013-11-20T19:28:13Z

On 20 November 2013 19:21, Christoffer Dall <christoffer.dall@linaro.org> wrote:
> On Wed, Nov 20, 2013 at 07:12:42PM +0000, Peter Maydell wrote:
>> Tangential, but your phrasing prompted me to ask: how does
>> the "start in PSCI power-off" boot protocol work for system reset?
>> Since the kernel doesn't currently provide a "reset this v CPU"
>> ioctl userspace has to do reset manually[*]; how do we say "take
>> this vCPU which has started up and run once, and put it back
>> into PSCI power-off" ?
>>
>> [*] this is pretty tedious, since it involves reading every CPU
>> register on the vCPU before first run in order to feed the kernel
>> back a bunch of info it already knows about the reset state of
>> a vCPU.
>>
> So, from looking at the code and the API specification calling
> KVM_ARM_VCPU_INIT does exactly this and also resets all core and cp15
> registers for you - you would here be able to set the power-off flag and
> pause those CPUs so PSCI can wake them up again.
>
> Am I missing something here?

Well, we call KVM_ARM_VCPU_INIT as part of our CPU init,
but I didn't think you were allowed to call it a second time
later on to do a CPU reset (ie as part of system reset when
the guest asks for a system reset as part of 'shutdown -r now').
Is that valid? If so, it would probably be good to specifically document it...

-- PMM