[xen master] x86: update GADDR based secondary time area

[patchbot@xxxxxxx]

commit c2e285ea0e6dea9cc6f4578e49d76075a153baa0
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Mon Oct 2 17:11:22 2023 +0200
Commit:     Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Thu Oct 5 14:08:57 2023 +0100

    x86: update GADDR based secondary time area
    
    Before adding a new vCPU operation to register the secondary time area
    by guest-physical address, add code to actually keep such areas up-to-
    date.
    
    Note that pages aren't marked dirty when written to (matching the
    handling of space mapped by map_vcpu_info()), on the basis that the
    registrations are lost anyway across migration (or would need re-
    populating at the target for transparent migration). Plus the contents
    of the areas in question have to be deemed volatile in the first place
    (so saving a "most recent" value is pretty meaningless even for e.g.
    snapshotting).
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Release-acked-by: Henry Wang <Henry.Wang@xxxxxxx>
---
 xen/arch/x86/time.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index af40a9993c..332d2d79ae 100644
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -1566,12 +1566,34 @@ static void __update_vcpu_system_time(struct vcpu *v, 
int force)
         v->arch.pv.pending_system_time = _u;
 }
 
+static void write_time_guest_area(struct vcpu_time_info *map,
+                                  const struct vcpu_time_info *src)
+{
+    /* 1. Update userspace version. */
+    write_atomic(&map->version, src->version);
+    smp_wmb();
+
+    /* 2. Update all other userspace fields. */
+    *map = *src;
+
+    /* 3. Update userspace version again. */
+    smp_wmb();
+    write_atomic(&map->version, version_update_end(src->version));
+}
+
 bool update_secondary_system_time(struct vcpu *v,
                                   struct vcpu_time_info *u)
 {
     XEN_GUEST_HANDLE(vcpu_time_info_t) user_u = v->arch.time_info_guest;
+    struct vcpu_time_info *map = v->arch.time_guest_area.map;
     struct guest_memory_policy policy = { .nested_guest_mode = false };
 
+    if ( map )
+    {
+        write_time_guest_area(map, u);
+        return true;
+    }
+
     if ( guest_handle_is_null(user_u) )
         return true;
 
--
generated by git-patchbot for /home/xen/git/xen.git#master