Ping: [PATCH 3/5] x86/PV: drop a few misleading paging_mode_refcounts() checks

[Jan Beulich <jbeulich@suse.com>]

On 15.07.2020 11:59, Jan Beulich wrote:
> The filling and cleaning up of v->arch.guest_table in new_guest_cr3()
> was apparently inconsistent so far: There was a type ref acquired
> unconditionally for the new top level page table, but the dropping of
> the old type ref was conditional upon !paging_mode_refcounts(). Mirror
> this also to arch_set_info_guest().
> 
> Also move new_guest_cr3()'s #ifdef to around the function - both callers
> now get built only when CONFIG_PV, i.e. no need to retain a stub.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

While I've got an ack from Tim, I think I need either an ack from
Andrew or someone's R-b in order to commit this.

Thanks, Jan

> --- a/xen/arch/x86/domain.c
> +++ b/xen/arch/x86/domain.c
> @@ -1122,8 +1122,6 @@ int arch_set_info_guest(
>  
>      if ( !cr3_page )
>          rc = -EINVAL;
> -    else if ( paging_mode_refcounts(d) )
> -        /* nothing */;
>      else if ( cr3_page == v->arch.old_guest_table )
>      {
>          v->arch.old_guest_table = NULL;
> @@ -1144,8 +1142,7 @@ int arch_set_info_guest(
>          case -ERESTART:
>              break;
>          case 0:
> -            if ( !compat && !VM_ASSIST(d, m2p_strict) &&
> -                 !paging_mode_refcounts(d) )
> +            if ( !compat && !VM_ASSIST(d, m2p_strict) )
>                  fill_ro_mpt(cr3_mfn);
>              break;
>          default:
> @@ -1166,7 +1163,7 @@ int arch_set_info_guest(
>  
>              if ( !cr3_page )
>                  rc = -EINVAL;
> -            else if ( !paging_mode_refcounts(d) )
> +            else
>              {
>                  rc = get_page_type_preemptible(cr3_page, PGT_root_page_table);
>                  switch ( rc )
> --- a/xen/arch/x86/mm.c
> +++ b/xen/arch/x86/mm.c
> @@ -3149,9 +3149,9 @@ int vcpu_destroy_pagetables(struct vcpu
>      return rc;
>  }
>  
> +#ifdef CONFIG_PV
>  int new_guest_cr3(mfn_t mfn)
>  {
> -#ifdef CONFIG_PV
>      struct vcpu *curr = current;
>      struct domain *d = curr->domain;
>      int rc;
> @@ -3220,7 +3220,7 @@ int new_guest_cr3(mfn_t mfn)
>  
>      pv_destroy_ldt(curr); /* Unconditional TLB flush later. */
>  
> -    if ( !VM_ASSIST(d, m2p_strict) && !paging_mode_refcounts(d) )
> +    if ( !VM_ASSIST(d, m2p_strict) )
>          fill_ro_mpt(mfn);
>      curr->arch.guest_table = pagetable_from_mfn(mfn);
>      update_cr3(curr);
> @@ -3231,30 +3231,24 @@ int new_guest_cr3(mfn_t mfn)
>      {
>          struct page_info *page = mfn_to_page(old_base_mfn);
>  
> -        if ( paging_mode_refcounts(d) )
> -            put_page(page);
> -        else
> -            switch ( rc = put_page_and_type_preemptible(page) )
> -            {
> -            case -EINTR:
> -            case -ERESTART:
> -                curr->arch.old_guest_ptpg = NULL;
> -                curr->arch.old_guest_table = page;
> -                curr->arch.old_guest_table_partial = (rc == -ERESTART);
> -                rc = -ERESTART;
> -                break;
> -            default:
> -                BUG_ON(rc);
> -                break;
> -            }
> +        switch ( rc = put_page_and_type_preemptible(page) )
> +        {
> +        case -EINTR:
> +        case -ERESTART:
> +            curr->arch.old_guest_ptpg = NULL;
> +            curr->arch.old_guest_table = page;
> +            curr->arch.old_guest_table_partial = (rc == -ERESTART);
> +            rc = -ERESTART;
> +            break;
> +        default:
> +            BUG_ON(rc);
> +            break;
> +        }
>      }
>  
>      return rc;
> -#else
> -    ASSERT_UNREACHABLE();
> -    return -EINVAL;
> -#endif
>  }
> +#endif
>  
>  #ifdef CONFIG_PV
>  static int vcpumask_to_pcpumask(
> 
>