[PATCH v4 5/9] x86/mem-sharing: copy GADDR based shared guest areas

[Jan Beulich <jbeulich@xxxxxxxx>]

In preparation of the introduction of new vCPU operations allowing to
register the respective areas (one of the two is x86-specific) by
guest-physical address, add the necessary fork handling (with the
backing function yet to be filled in).

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v3: Extend comment.

--- a/xen/arch/x86/mm/mem_sharing.c
+++ b/xen/arch/x86/mm/mem_sharing.c
@@ -1641,6 +1641,68 @@ static void copy_vcpu_nonreg_state(struc
     hvm_set_nonreg_state(cd_vcpu, &nrs);
 }
 
+static int copy_guest_area(struct guest_area *cd_area,
+                           const struct guest_area *d_area,
+                           struct vcpu *cd_vcpu,
+                           const struct domain *d)
+{
+    mfn_t d_mfn, cd_mfn;
+
+    if ( !d_area->pg )
+        return 0;
+
+    d_mfn = page_to_mfn(d_area->pg);
+
+    /* Allocate & map a page for the area if it hasn't been already. */
+    if ( !cd_area->pg )
+    {
+        gfn_t gfn = mfn_to_gfn(d, d_mfn);
+        struct p2m_domain *p2m = p2m_get_hostp2m(cd_vcpu->domain);
+        p2m_type_t p2mt;
+        p2m_access_t p2ma;
+        unsigned int offset;
+        int ret;
+
+        cd_mfn = p2m->get_entry(p2m, gfn, &p2mt, &p2ma, 0, NULL, NULL);
+        if ( mfn_eq(cd_mfn, INVALID_MFN) )
+        {
+            struct page_info *pg = alloc_domheap_page(cd_vcpu->domain, 0);
+
+            if ( !pg )
+                return -ENOMEM;
+
+            cd_mfn = page_to_mfn(pg);
+            set_gpfn_from_mfn(mfn_x(cd_mfn), gfn_x(gfn));
+
+            ret = p2m->set_entry(p2m, gfn, cd_mfn, PAGE_ORDER_4K, p2m_ram_rw,
+                                 p2m->default_access, -1);
+            if ( ret )
+                return ret;
+        }
+        else if ( p2mt != p2m_ram_rw )
+            return -EBUSY;
+
+        /*
+         * Map the area into the guest. For simplicity specify the entire range
+         * up to the end of the page: All the function uses it for is to check
+         * that the range doesn't cross page boundaries. Having the area mapped
+         * in the original domain implies that it fits there and therefore will
+         * also fit in the clone.
+         */
+        offset = PAGE_OFFSET(d_area->map);
+        ret = map_guest_area(cd_vcpu, gfn_to_gaddr(gfn) + offset,
+                             PAGE_SIZE - offset, cd_area, NULL);
+        if ( ret )
+            return ret;
+    }
+    else
+        cd_mfn = page_to_mfn(cd_area->pg);
+
+    copy_domain_page(cd_mfn, d_mfn);
+
+    return 0;
+}
+
 static int copy_vpmu(struct vcpu *d_vcpu, struct vcpu *cd_vcpu)
 {
     struct vpmu_struct *d_vpmu = vcpu_vpmu(d_vcpu);
@@ -1733,6 +1795,16 @@ static int copy_vcpu_settings(struct dom
             copy_domain_page(new_vcpu_info_mfn, vcpu_info_mfn);
         }
 
+        /* Same for the (physically registered) runstate and time info areas. 
*/
+        ret = copy_guest_area(&cd_vcpu->runstate_guest_area,
+                              &d_vcpu->runstate_guest_area, cd_vcpu, d);
+        if ( ret )
+            return ret;
+        ret = copy_guest_area(&cd_vcpu->arch.time_guest_area,
+                              &d_vcpu->arch.time_guest_area, cd_vcpu, d);
+        if ( ret )
+            return ret;
+
         ret = copy_vpmu(d_vcpu, cd_vcpu);
         if ( ret )
             return ret;
@@ -1974,7 +2046,10 @@ int mem_sharing_fork_reset(struct domain
 
  state:
     if ( reset_state )
+    {
         rc = copy_settings(d, pd);
+        /* TBD: What to do here with -ERESTART? */
+    }
 
     domain_unpause(d);
 
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -1601,6 +1601,13 @@ void unmap_vcpu_info(struct vcpu *v)
     put_page_and_type(mfn_to_page(mfn));
 }
 
+int map_guest_area(struct vcpu *v, paddr_t gaddr, unsigned int size,
+                   struct guest_area *area,
+                   void (*populate)(void *dst, struct vcpu *v))
+{
+    return -EOPNOTSUPP;
+}
+
 /*
  * This is only intended to be used for domain cleanup (or more generally only
  * with at least the respective vCPU, if it's not the current one, reliably