[Xen-devel] [PATCH 1/2] x86/shim: suspend and resume platform time correctly

[Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>]

Similarly to S3, platform time needs to be saved on guest suspend
and restored on resume respectively. This should account for expected
jumps in PV clock counter value after resume. time_suspend/resume()
are safe to use in PVH setting as is since any existing operations
with PIT that they do would simply be ignored there.

Additionally, add resume callback for Xen PV clocksource to avoid
its breakage on migration.

Signed-off-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
---
 xen/arch/x86/pv/shim.c |  7 ++++++-
 xen/arch/x86/time.c    | 12 +++++++++---
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/pv/shim.c b/xen/arch/x86/pv/shim.c
index 7a898fd..6b26eaa 100644
--- a/xen/arch/x86/pv/shim.c
+++ b/xen/arch/x86/pv/shim.c
@@ -325,9 +325,13 @@ int pv_shim_shutdown(uint8_t reason)
         if ( v != current )
             vcpu_pause_by_systemcontroller(v);
 
+    /* Prepare timekeeping code to suspend.*/
+    time_suspend();
+
     rc = xen_hypercall_shutdown(SHUTDOWN_suspend);
     if ( rc )
     {
+        time_resume();
         for_each_vcpu ( d, v )
             if ( v != current )
                 vcpu_unpause_by_systemcontroller(v);
@@ -335,8 +339,9 @@ int pv_shim_shutdown(uint8_t reason)
         return rc;
     }
 
-    /* Resume the shim itself first. */
+    /* Resume the shim itself and timekeeping first. */
     hypervisor_resume();
+    time_resume();
 
     /*
      * ATM there's nothing Xen can do if the console/store pfn changes,
diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index f6b26f8..7e7a62e 100644
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -565,6 +565,7 @@ static struct platform_timesource __initdata plt_tsc =
  *
  * Xen clock source is a variant of TSC source.
  */
+static uint64_t xen_timer_last;
 
 static uint64_t xen_timer_cpu_frequency(void)
 {
@@ -610,7 +611,6 @@ static uint64_t read_xen_timer(void)
     uint32_t version;
     uint64_t ret;
     uint64_t last;
-    static uint64_t last_value;
 
     do {
         version = info->version & ~1;
@@ -626,20 +626,26 @@ static uint64_t read_xen_timer(void)
 
     /* Maintain a monotonic global value */
     do {
-        last = read_atomic(&last_value);
+        last = read_atomic(&xen_timer_last);
         if ( ret < last )
             return last;
-    } while ( unlikely(cmpxchg(&last_value, last, ret) != last) );
+    } while ( unlikely(cmpxchg(&xen_timer_last, last, ret) != last) );
 
     return ret;
 }
 
+static void resume_xen_timer(struct platform_timesource *pts)
+{
+    write_atomic(&xen_timer_last, 0);
+}
+
 static struct platform_timesource __initdata plt_xen_timer =
 {
     .id = "xen",
     .name = "XEN PV CLOCK",
     .read_counter = read_xen_timer,
     .init = init_xen_timer,
+    .resume = resume_xen_timer,
     .counter_bits = 63,
 };
 #endif
-- 
2.7.4


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