Re: [PATCH] x86/xen: Add support for HVMOP_set_evtchn_upcall_vector

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 7/11/22 11:22 AM, Jane Malalane wrote:
> --- a/arch/x86/xen/enlighten_hvm.c
> +++ b/arch/x86/xen/enlighten_hvm.c
> @@ -7,6 +7,7 @@
>   
>   #include <xen/features.h>
>   #include <xen/events.h>
> +#include <xen/interface/hvm/hvm_op.h>
>   #include <xen/interface/memory.h>
>   
>   #include <asm/apic.h>
> @@ -30,6 +31,9 @@
>   
>   static unsigned long shared_info_pfn;
>   
> +__ro_after_init bool xen_ack_upcall;
> +EXPORT_SYMBOL_GPL(xen_ack_upcall);

Shouldn't this be called something like xen_percpu_upcall?


> +
>   void xen_hvm_init_shared_info(void)
>   {
>         struct xen_add_to_physmap xatp;
> @@ -125,6 +129,9 @@ DEFINE_IDTENTRY_SYSVEC(sysvec_xen_hvm_callback)
>   {
>         struct pt_regs *old_regs = set_irq_regs(regs);
>   
> +	if (xen_ack_upcall)
> +               ack_APIC_irq();
> +
>         inc_irq_stat(irq_hv_callback_count);
>   
>   	xen_hvm_evtchn_do_upcall();
> @@ -168,6 +175,15 @@ static int xen_cpu_up_prepare_hvm(unsigned int cpu)
>         if (!xen_have_vector_callback)
>                 return 0;
>   
> +	if (xen_ack_upcall) {
> +               xen_hvm_evtchn_upcall_vector_t op = {
> +                       .vector = HYPERVISOR_CALLBACK_VECTOR,
> +                       .vcpu = per_cpu(xen_vcpu_id, cpu),
> +               };
> +
> +               BUG_ON(HYPERVISOR_hvm_op(HVMOP_set_evtchn_upcall_vector, &op));

Does this have to be fatal? Can't we just fail bringing this vcpu up?


> +       }
> +
>         if (xen_feature(XENFEAT_hvm_safe_pvclock))
>                 xen_setup_timer(cpu);
>   
> @@ -211,8 +227,7 @@ static void __init xen_hvm_guest_init(void)
>   
>   	xen_panic_handler_init();
>   
> -	if (!no_vector_callback && xen_feature(XENFEAT_hvm_callback_vector))
> -               xen_have_vector_callback = 1;
> +       xen_have_vector_callback = !no_vector_callback;

Can we get rid of one of those two variables then?


>   
>   	xen_hvm_smp_init();
>         WARN_ON(xen_cpuhp_setup(xen_cpu_up_prepare_hvm, xen_cpu_dead_hvm));
> diff --git a/arch/x86/xen/suspend_hvm.c b/arch/x86/xen/suspend_hvm.c
> index 9d548b0c772f..be66e027ef28 100644
> --- a/arch/x86/xen/suspend_hvm.c
> +++ b/arch/x86/xen/suspend_hvm.c
> @@ -5,6 +5,7 @@
>   #include <xen/hvm.h>
>   #include <xen/features.h>
>   #include <xen/interface/features.h>
> +#include <xen/events.h>
>   
>   #include "xen-ops.h"
>   
> @@ -14,6 +15,23 @@ void xen_hvm_post_suspend(int suspend_cancelled)
>                 xen_hvm_init_shared_info();
>                 xen_vcpu_restore();
>         }
> -       xen_setup_callback_vector();
> +       if (xen_ack_upcall) {
> +               unsigned int cpu;
> +
> +               for_each_online_cpu(cpu) {
> +                       xen_hvm_evtchn_upcall_vector_t op = {
> +                                       .vector = HYPERVISOR_CALLBACK_VECTOR,
> +                                       .vcpu = per_cpu(xen_vcpu_id, cpu),
> +                       };
> +
> +                       BUG_ON(HYPERVISOR_hvm_op(HVMOP_set_evtchn_upcall_vector,
> +                                                &op));
> +                       /* Trick toolstack to think we are enlightened. */
> +                       if (!cpu)
> +                               BUG_ON(xen_set_callback_via(1));

What are you trying to make the toolstack aware of? That we have *a* callback 
(either global or percpu)?


BTW, you can take it out the loop. And maybe @op definition too, except for 
.vcpu assignment.


> +               }
> +       } else {
> +               xen_setup_callback_vector();
> +       }
>         xen_unplug_emulated_devices();
>   }

-boris