Re: [Xen-devel] xc_hvm_inject_trap() races

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.11.16 at 15:34, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> My proposal was simply something along the lines of:
> 
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> index 704fd64..58f5ae4 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -535,8 +535,22 @@ void hvm_do_resume(struct vcpu *v)
>      /* Inject pending hw/sw trap */
>      if ( v->arch.hvm_vcpu.inject_trap.vector != -1 )
>      {
> -        hvm_inject_trap(&v->arch.hvm_vcpu.inject_trap);
> +        unsigned int success = 0;
> +
> +        /* Check for already pending interrupts (races). */
> +        if ( !hvm_event_pending(v) )
> +        {
> +            hvm_inject_trap(&v->arch.hvm_vcpu.inject_trap);
> +            success = 1;
> +        }
> +
>          v->arch.hvm_vcpu.inject_trap.vector = -1;
> +
> +        hvm_monitor_injection_result(v->arch.hvm_vcpu.inject_trap.vector,
> +                                     v->arch.hvm_vcpu.inject_trap.type,
> +
> v->arch.hvm_vcpu.inject_trap.error_code,
> +                                     v->arch.hvm_vcpu.inject_trap.cr2,
> +                                     success);
>      }
>  }
> 

But you realize that injection isn't really VM event related; it's an
independent interface. Hence my "too special cased"complaint.
What if the event I did propose would be a one shot one, which
you enable right before (or after) doing your event injection (it
could also be an injection flag)? You'd then see whether the
next event the vCPU gets is the one you tried to inject.

Jan


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