Re: [Xen-devel] [PATCH] multicall: don't ignore failure from __copy_to_guest() upon preemption

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 11/11/2011 11:16, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:

> At once adjust perf counter updates to also count calls from here even
> if a guest memory access failed.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Acked-by: Keir Fraser <keir@xxxxxxx>

> --- a/xen/common/multicall.c
> +++ b/xen/common/multicall.c
> @@ -25,6 +25,7 @@ do_multicall(
>  {
>      struct mc_state *mcs = &current->mc_state;
>      unsigned int     i;
> +    int              rc = 0;
>  
>      if ( unlikely(__test_and_set_bit(_MCSF_in_multicall, &mcs->flags)) )
>      {
> @@ -33,15 +34,18 @@ do_multicall(
>      }
>  
>      if ( unlikely(!guest_handle_okay(call_list, nr_calls)) )
> -        goto fault;
> +        rc = -EFAULT;
>  
> -    for ( i = 0; i < nr_calls; i++ )
> +    for ( i = 0; !rc && i < nr_calls; i++ )
>      {
>          if ( hypercall_preempt_check() )
>              goto preempted;
>  
>          if ( unlikely(__copy_from_guest(&mcs->call, call_list, 1)) )
> -            goto fault;
> +        {
> +            rc = -EFAULT;
> +            break;
> +        }
>  
>          do_multicall_call(&mcs->call);
>  
> @@ -58,30 +62,25 @@ do_multicall(
>  #endif
>  
>          if ( unlikely(__copy_field_to_guest(call_list, &mcs->call, result)) )
> -            goto fault;
> -
> -        if ( test_bit(_MCSF_call_preempted, &mcs->flags) )
> +            rc = -EFAULT;
> +        else if ( test_bit(_MCSF_call_preempted, &mcs->flags) )
>          {
>              /* Translate sub-call continuation to guest layout */
>              xlat_multicall_entry(mcs);
>  
>              /* Copy the sub-call continuation. */
> -            (void)__copy_to_guest(call_list, &mcs->call, 1);
> -            goto preempted;
> +            if ( likely(!__copy_to_guest(call_list, &mcs->call, 1)) )
> +                goto preempted;
> +            rc = -EFAULT;
>          }
> -
> -        guest_handle_add_offset(call_list, 1);
> +        else
> +            guest_handle_add_offset(call_list, 1);
>      }
>  
>      perfc_incr(calls_to_multicall);
> -    perfc_add(calls_from_multicall, nr_calls);
> -    mcs->flags = 0;
> -    return 0;
> -
> - fault:
> -    perfc_incr(calls_to_multicall);
> +    perfc_add(calls_from_multicall, i);
>      mcs->flags = 0;
> -    return -EFAULT;
> +    return rc;
>  
>   preempted:
>      perfc_add(calls_from_multicall, i);
> 
> 
> 
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> http://lists.xensource.com/xen-devel



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