Re: [Xen-devel] [RFC] x86/vm_event: Allow returning i-cache for emulation

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 9 Sep 2016, Tamas K Lengyel wrote:
> When emulating instructions the emulator maintains a small i-cache fetched
> from the guest memory. Under certain scenarios this memory region may contain
> instructions that a monitor subscriber would prefer to hide, namely INT3, and
> instead would prefer to emulate a different instruction in-place.
> 
> This patch extends the vm_event interface to allow returning this i-cache via
> the vm_event response.
> 
> Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>
>
> diff --git a/xen/common/vm_event.c b/xen/common/vm_event.c
> index 8398af7..161d149 100644
> --- a/xen/common/vm_event.c
> +++ b/xen/common/vm_event.c
> @@ -407,8 +407,11 @@ void vm_event_resume(struct domain *d, struct 
> vm_event_domain *ved)
>              vm_event_register_write_resume(v, &rsp);
>              break;
>  
> +        case VM_EVENT_REASON_SOFTWARE_BREAKPOINT:
> +            vm_event_interrupt_emulate_check(v, &rsp);
> +            break;
> +
>  #ifdef CONFIG_HAS_MEM_ACCESS
> -        case VM_EVENT_REASON_MEM_ACCESS:
>              mem_access_resume(v, &rsp);
>              break;
>  #endif
> diff --git a/xen/include/asm-arm/vm_event.h b/xen/include/asm-arm/vm_event.h
> index ccc4b60..e56bc78 100644
> --- a/xen/include/asm-arm/vm_event.h
> +++ b/xen/include/asm-arm/vm_event.h
> @@ -40,6 +40,12 @@ static inline void vm_event_toggle_singlestep(struct 
> domain *d, struct vcpu *v)
>  }
>  
>  static inline
> +void vm_event_interrupt_emulate_check(struct vcpu *v, vm_event_response_t 
> *rsp)
> +{
> +    /* Not supported on ARM. */
> +}
> +
> +static inline
>  void vm_event_register_write_resume(struct vcpu *v, vm_event_response_t *rsp)
>  {
>      /* Not supported on ARM. */

Doesn't it make sense to return some sort of error?

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