Re: [PATCH v10 47/59] i386/xen: handle PV timer hypercalls

[Paul Durrant]

On 01/02/2023 14:31, David Woodhouse wrote:
> From: Joao Martins <joao.m.martins@oracle.com>
>
> Introduce support for one shot and periodic mode of Xen PV timers,
> whereby timer interrupts come through a special virq event channel
> with deadlines being set through:
>
> 1) set_timer_op hypercall (only oneshot)
> 2) vcpu_op hypercall for {set,stop}_{singleshot,periodic}_timer
> hypercalls
>
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> ---
>   hw/i386/kvm/xen_evtchn.c  |  31 +++++
>   hw/i386/kvm/xen_evtchn.h  |   2 +
>   target/i386/cpu.h         |   5 +
>   target/i386/kvm/xen-emu.c | 245 +++++++++++++++++++++++++++++++++++++-
>   target/i386/machine.c     |   1 +
>   5 files changed, 282 insertions(+), 2 deletions(-)
[snip]
> @@ -1246,6 +1466,9 @@ static bool do_kvm_xen_handle_exit(X86CPU *cpu, struct 
> kvm_xen_exit *exit)
>       }
>   
>       switch (code) {
> +    case __HYPERVISOR_set_timer_op:
> +        return kvm_xen_hcall_set_timer_op(exit, cpu,
> +                                          exit->u.hcall.params[0]);

There's a nasty little semantic subtlety here which has been missed... 
If the guest is not in longmode then the timer value is actually split 
across param[0] and param[1] (so that it is still 64-bits).

  Paul