On 07/09/15 17:45, Eric Auger wrote:
> Hi Christoffer,
> On 09/04/2015 09:40 PM, Christoffer Dall wrote:
>> Forwarded physical interrupts on arm/arm64 is a tricky concept and the
>> way we deal with them is not apparently easy to understand by reading
>> various specs.
>>
>> Therefore, add a proper documentation file explaining the flow and
>> rationale of the behavior of the vgic.
>>
>> Some of this text was contributed by Marc Zyngier and edited by me.
>> Omissions and errors are all mine.
>>
>> Signed-off-by: Christoffer Dall <[email protected]>
>> ---
>> Documentation/virtual/kvm/arm/vgic-mapped-irqs.txt | 181
>> +++++++++++++++++++++
>> 1 file changed, 181 insertions(+)
>> create mode 100644 Documentation/virtual/kvm/arm/vgic-mapped-irqs.txt
>>
>> diff --git a/Documentation/virtual/kvm/arm/vgic-mapped-irqs.txt
>> b/Documentation/virtual/kvm/arm/vgic-mapped-irqs.txt
>> new file mode 100644
>> index 0000000..24b6f28
>> --- /dev/null
>> +++ b/Documentation/virtual/kvm/arm/vgic-mapped-irqs.txt
>> @@ -0,0 +1,181 @@
>> +KVM/ARM VGIC Forwarded Physical Interrupts
>> +==========================================
[...]
>> +1. KVM runs the VCPU
>> +2. The guest programs the time to fire in T+100
>> +4. At T+100 the timer fires and a physical IRQ causes the VM to exit
>> +5. With interrupts disabled on the CPU, KVM looks at the timer state
>> + and injects a forwarded physical interrupt because it concludes the
>> + timer has expired.
> I don't get how we can trap without the virtual timer PPI handler being
> entered on host side. Please can you elaborate on this?
On VM exit, we disable the virtual timer (see the code in
hyp.S::save_timer_state where we clear the enable bit). We still perform
the exit, but the cause for exit is now gone, and the handler will never
fire.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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