[PATCH v6 06/10] x86/mem-sharing: copy GADDR based shared guest areas

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

From: 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>
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Changes since v5:
 - Convert -ERESTART to -EAGAIN.

Changes since v4:
 - Rely on map_guest_area() to populate the child p2m if necessary.
---
 xen/arch/x86/mm/mem_sharing.c | 36 +++++++++++++++++++++++++++++++++++
 xen/common/domain.c           |  7 +++++++
 2 files changed, 43 insertions(+)

diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
index 5f8f1fb4d871..445947b6a918 100644
--- a/xen/arch/x86/mm/mem_sharing.c
+++ b/xen/arch/x86/mm/mem_sharing.c
@@ -1641,6 +1641,24 @@ static void copy_vcpu_nonreg_state(struct vcpu *d_vcpu, 
struct vcpu *cd_vcpu)
     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)
+{
+    unsigned int offset;
+
+    /* Check if no area to map, or already mapped. */
+    if ( !d_area->pg || cd_area->pg )
+        return 0;
+
+    offset = PAGE_OFFSET(d_area->map);
+    return map_guest_area(cd_vcpu, gfn_to_gaddr(
+                                       mfn_to_gfn(d, page_to_mfn(d_area->pg))) 
+
+                                   offset,
+                          PAGE_SIZE - offset, cd_area, NULL);
+}
+
 static int copy_vpmu(struct vcpu *d_vcpu, struct vcpu *cd_vcpu)
 {
     struct vpmu_struct *d_vpmu = vcpu_vpmu(d_vcpu);
@@ -1709,6 +1727,16 @@ static int copy_vcpu_settings(struct domain *cd, const 
struct domain *d)
                 return ret;
         }
 
+        /* 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;
@@ -1950,7 +1978,15 @@ int mem_sharing_fork_reset(struct domain *d, bool 
reset_state,
 
  state:
     if ( reset_state )
+    {
         rc = copy_settings(d, pd);
+        if ( rc == -ERESTART )
+            /*
+             * Translate to -EAGAIN, see TODO comment at top of function about
+             * hypercall continuations.
+             */
+            rc = -EAGAIN;
+    }
 
     domain_unpause(d);
 
diff --git a/xen/common/domain.c b/xen/common/domain.c
index d4958ec5e149..47fc90271901 100644
--- 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
-- 
2.42.0