Re: [Xen-devel] [PATCH 2/9] x86/pv: Support do_set_segment_base() for compat guests

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.07.16 at 11:51, <andrew.cooper3@xxxxxxxxxx> wrote:
> set_segment_base is the only hypercall exists in only one of the two modes
> guests might run in; all other hypercalls are either implemented, or
> unimplemented in both modes.
> 
> Remove this split, by allowing do_set_segment_base() to be called in the
> compat hypercall path.  This change will simplify the verification logic in a
> later change.
> 
> No behavioural change from a guests point of view.

Nevertheless I don't view this as a reasonable change on its own:

> --- a/xen/arch/x86/x86_64/compat/entry.S
> +++ b/xen/arch/x86/x86_64/compat/entry.S
> @@ -453,7 +453,7 @@ ENTRY(compat_hypercall_table)
>          .quad compat_update_va_mapping_otherdomain
>          .quad compat_iret
>          .quad compat_vcpu_op
> -        .quad compat_ni_hypercall       /* 25 */
> +        .quad do_set_segment_base       /* 25 */

This part will (I suppose) be deleted by a later change.

> --- a/xen/arch/x86/x86_64/mm.c
> +++ b/xen/arch/x86/x86_64/mm.c
> @@ -1031,6 +1031,9 @@ long do_set_segment_base(unsigned int which, unsigned 
> long base)
>      struct vcpu *v = current;
>      long ret = 0;
>  
> +    if ( is_pv_32bit_vcpu(v) )
> +        return -ENOSYS; /* x86/64 only. */

And this addition could as well happen when that later change
does the re-org.

Jan


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