Re: [Xen-devel] [PATCH] x86/domain: Improvements to switch_native() and switch_compat()

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.01.15 at 11:44, <andrew.cooper3@xxxxxxxxxx> wrote:
> To aid the cleanup in switch_compat(), release_compat_l4() is updated to 
> make
> it safe to call on a vcpu without an existing compat l4.

For this part of the change:

> --- a/xen/arch/x86/domain.c
> +++ b/xen/arch/x86/domain.c
> @@ -349,6 +349,8 @@ static int setup_compat_l4(struct vcpu *v)
>  
>  static void release_compat_l4(struct vcpu *v)
>  {
> +    if ( pagetable_is_null(v->arch.guest_table) )
> +        return;

I'd rather see this check be done in the one caller that needs it,
since ...

> @@ -373,21 +373,16 @@ int switch_native(struct domain *d)
>  
>      d->arch.is_32bit_pv = d->arch.has_32bit_shinfo = 0;
>  
> -    for ( vcpuid = 0; vcpuid < d->max_vcpus; vcpuid++ )
> -    {
> -        if (d->vcpu[vcpuid])
> -            release_compat_l4(d->vcpu[vcpuid]);
> -    }
> +    for_each_vcpu( d, v )
> +        release_compat_l4(v);

... this one can't run into that situation (or the old code would have
been broken).

Jan


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