[PATCH v3 10/12] x86/shadow: make monitor table create/destroy more consistent

[Jan Beulich <jbeulich@xxxxxxxx>]

While benign at present, it is still a little fragile to operate on a
wrong "old_mode" value in sh_update_paging_modes(). This can happen when
no monitor table was present initially - we'd create one for the new
mode without updating old_mode. Correct this in two ways, each of which
would be sufficient on its own: Once by adding "else" to the second of
the involved if()s in the function, and then by setting the correct
initial mode for HVM domains in shadow_vcpu_init().

Further use the same predicate (paging_mode_external()) consistently
when dealing with shadow mode init/update/cleanup, rather than a mix of
is_hvm_vcpu() (init), is_hvm_domain() (update), and
paging_mode_external() (cleanup).

Finally drop a redundant is_hvm_domain() from inside the bigger if()
(which is being converted to paging_mode_external()) in
sh_update_paging_modes().

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: Style adjustment.

--- a/xen/arch/x86/mm/shadow/common.c
+++ b/xen/arch/x86/mm/shadow/common.c
@@ -119,9 +119,9 @@ void shadow_vcpu_init(struct vcpu *v)
     }
 #endif
 
-    v->arch.paging.mode = is_hvm_vcpu(v) ?
-                          &SHADOW_INTERNAL_NAME(sh_paging_mode, 3) :
-                          &SHADOW_INTERNAL_NAME(sh_paging_mode, 4);
+    v->arch.paging.mode = paging_mode_external(v->domain)
+                          ? &SHADOW_INTERNAL_NAME(sh_paging_mode, 2)
+                          : &SHADOW_INTERNAL_NAME(sh_paging_mode, 4);
 }
 
 #if SHADOW_AUDIT
@@ -1801,7 +1801,7 @@ static void sh_update_paging_modes(struc
         sh_detach_old_tables(v);
 
 #ifdef CONFIG_HVM
-    if ( is_hvm_domain(d) )
+    if ( paging_mode_external(d) )
     {
         const struct paging_mode *old_mode = v->arch.paging.mode;
 
@@ -1854,13 +1854,12 @@ static void sh_update_paging_modes(struc
             make_cr3(v, mmfn);
             hvm_update_host_cr3(v);
         }
-
-        if ( v->arch.paging.mode != old_mode )
+        else if ( v->arch.paging.mode != old_mode )
         {
             SHADOW_PRINTK("new paging mode: %pv pe=%d gl=%u "
                           "sl=%u (was g=%u s=%u)\n",
                           v,
-                          is_hvm_domain(d) ? hvm_paging_enabled(v) : 1,
+                          hvm_paging_enabled(v),
                           v->arch.paging.mode->guest_levels,
                           v->arch.paging.mode->shadow.shadow_levels,
                           old_mode ? old_mode->guest_levels : 0,