x86/np2m: implement sharing of np2m between vCPUs

At the moment, nested p2ms are not shared between vcpus even if they
share the same base pointer.

Modify p2m_get_nestedp2m() to allow sharing a np2m between multiple
vcpus with the same np2m_base (L1 np2m_base value in VMCx12).

If the current np2m doesn't match the current base pointer, first look
for another nested p2m in the same domain with the same base pointer,
before reclaiming one from the LRU.

Signed-off-by: Sergey Dyasli <sergey.dyasli@citrix.com>
Signed-off-by: George Dunlap <george.dunlap@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jun Nakajima <jun.nakajima@intel.com>

xen/arch/x86/hvm/vmx/vvmx.c

@@ -1201,6 +1201,7 @@ static void virtual_vmentry(struct cpu_user_regs *regs)
 
     /* Setup virtual ETP for L2 guest*/
     if ( nestedhvm_paging_mode_hap(v) )
+        /* This will setup the initial np2m for the nested vCPU */
         __vmwrite(EPT_POINTER, get_shadow_eptp(v));
     else
         __vmwrite(EPT_POINTER, get_host_eptp(v));

xen/arch/x86/mm/p2m.c

@@ -1846,6 +1846,7 @@ p2m_get_nestedp2m_locked(struct vcpu *v)
     struct domain *d = v->domain;
     struct p2m_domain *p2m;
     uint64_t np2m_base = nhvm_vcpu_p2m_base(v);
+    unsigned int i;
 
     /* Mask out low bits; this avoids collisions with P2M_BASE_EADDR */
     np2m_base &= ~(0xfffull);
@@ -1859,19 +1860,19 @@ p2m_get_nestedp2m_locked(struct vcpu *v)
     if ( p2m ) 
     {
         p2m_lock(p2m);
-        if ( p2m->np2m_base == np2m_base || p2m->np2m_base == P2M_BASE_EADDR )
+        if ( p2m->np2m_base == np2m_base )
         {
             /* Check if np2m was flushed just before the lock */
-            if ( p2m->np2m_base == P2M_BASE_EADDR ||
-                 nv->np2m_generation != p2m->np2m_generation )
+            if ( nv->np2m_generation != p2m->np2m_generation )
                 nvcpu_flush(v);
+            /* np2m is up-to-date */
             p2m->np2m_base = np2m_base;
             assign_np2m(v, p2m);
             nestedp2m_unlock(d);
 
             return p2m;
         }
-        else
+        else if ( p2m->np2m_base != P2M_BASE_EADDR )
         {
             /* vCPU is switching from some other valid np2m */
             cpumask_clear_cpu(v->processor, p2m->dirty_cpumask);
@@ -1879,6 +1880,23 @@ p2m_get_nestedp2m_locked(struct vcpu *v)
         p2m_unlock(p2m);
     }
 
+    /* Share a np2m if possible */
+    for ( i = 0; i < MAX_NESTEDP2M; i++ )
+    {
+        p2m = d->arch.nested_p2m[i];
+        p2m_lock(p2m);
+        if ( p2m->np2m_base == np2m_base )
+        {
+            nvcpu_flush(v);
+            p2m->np2m_base = np2m_base;
+            assign_np2m(v, p2m);
+            nestedp2m_unlock(d);
+
+            return p2m;
+        }
+        p2m_unlock(p2m);
+    }
+
     /* All p2m's are or were in use. Take the least recent used one,
      * flush it and reuse. */
     p2m = p2m_getlru_nestedp2m(d, NULL);