Hi Marc, On 09/07/2015 07:50 PM, Marc Zyngier wrote: > 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 <christoffer.dall@xxxxxxxxxx> >>> --- >>> 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. OK thanks for the clarification Eric > > Thanks, > > M. > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
