Re: [RFC PATCH 18/21] kvm/ioapic: mark gsi-2 used in ioapic routing init

[Philippe Mathieu-Daudé]

On 5/12/22 18:31, David Woodhouse wrote:
> From: Ankur Arora <ankur.a.arora@oracle.com>
>
> GSI-2/IOAPIC pin-2 is treated specially while initing
> IRQ routing: PIC does not use it at all while the IOAPIC
> maps virq=0 to pin-2 and does not use GSI-2.
> (all other GSIs are identity mapped to pins.)
>
> This results in any later code which allocates a virq
> to be assigned GSI-2. This virq is in-turn used to
> remap interrupts to HYPERVISOR_CALLBACK_VECTOR (0xf3)
> to deliver to the guest.
>
> Ordinarily this would be okay, but if the event delivery is
> via direct injection via KVM_REQ_EVENT (without going
> through the LAPIC) we see vmentry failure.
>
> This works fine for any other values of GSI.
>
> As a workaround, mark GSI-2 used.
>
> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> ---
>   accel/kvm/kvm-all.c  | 5 +++++
>   hw/i386/kvm/ioapic.c | 1 +
>   include/sysemu/kvm.h | 1 +
>   3 files changed, 7 insertions(+)


> diff --git a/hw/i386/kvm/ioapic.c b/hw/i386/kvm/ioapic.c
> index ee7c8ef68b..5fab0d35c9 100644
> --- a/hw/i386/kvm/ioapic.c
> +++ b/hw/i386/kvm/ioapic.c
> @@ -43,6 +43,7 @@ void kvm_pc_setup_irq_routing(bool pci_enabled)
>               }
>           }
>       }

Workarounds usually deserve some comment in the code.

> +    kvm_irqchip_set_gsi(s, 2);
>       kvm_irqchip_commit_routes(s);
>   }