[PATCH for-4.22? 8/9] x86/domctl: don't imply I/O port permissions from I/O port mapping

[Jan Beulich <jbeulich@xxxxxxxx>]

Rather than granting permissions when mapping (an operation that DM-s are
allowed to carry out, while they can't invoke ioport-permission), check
whether permissions actually were granted when adding a mapping. This then
also allows relaxing the necessary locking.

Fixes: 192c4dabc344 ("domctl and p2m changes for PCI passthru")
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
libxl has libxl__grant_vga_iomem_permission(), but I can't spot any I/O
port equivalent (nor a revoke counterpart, btw). Everywhere else MMIO and
I/O ports look to be treated equally.

Qemu uses both xc_domain_{iomem_permission,memory_mapping}() in
igd_write_opregion(), but only xc_domain_{memory,ioport}_mapping() in
xen_pt_region_update() and xen_pt_{,un}register_vga_regions(). Is the IGD
region special in any way? Clearly this can't work from a stubdom.

--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -714,9 +714,14 @@ long arch_do_domctl(
             break;
 
         hvm = &d->arch.hvm;
-        iocaps_double_lock(d, true);
+        /*
+         * NB: The double lock isn't really needed when !add, but is used 
anyway
+         * to keep things simple.
+         */
+        iocaps_double_lock(d, false);
 
-        if ( !ioports_access_permitted(currd, fmp, fmp + np - 1) )
+        if ( !ioports_access_permitted(currd, fmp, fmp + np - 1) ||
+             (add && !ioports_access_permitted(d, fmp, fmp + np - 1)) )
             ret = -EPERM;
         else if ( add )
         {
@@ -747,15 +752,6 @@ long arch_do_domctl(
                 list_add_tail(&g2m_ioport->list, &hvm->g2m_ioport_list);
             }
             write_unlock(&hvm->g2m_ioport_lock);
-            if ( !ret )
-                ret = ioports_permit_access(d, fmp, fmp + np - 1);
-            if ( ret && !found && g2m_ioport )
-            {
-                write_lock(&hvm->g2m_ioport_lock);
-                list_del(&g2m_ioport->list);
-                write_unlock(&hvm->g2m_ioport_lock);
-                xfree(g2m_ioport);
-            }
         }
         else
         {
@@ -772,15 +768,9 @@ long arch_do_domctl(
                     break;
                 }
             write_unlock(&hvm->g2m_ioport_lock);
-
-            ret = ioports_deny_access(d, fmp, fmp + np - 1);
-            if ( ret && is_hardware_domain(currd) )
-                printk(XENLOG_ERR
-                       "ioport_map: error %ld denying dom%d access to 
[%x,%x]\n",
-                       ret, d->domain_id, fmp, fmp + np - 1);
         }
 
-        iocaps_double_unlock(d, true);
+        iocaps_double_unlock(d, false);
         break;
     }