x86/time: update TSC stamp on restore from deep C-state

If ITSC is not available on CPU (e.g if running nested as PV shim)
then X86_FEATURE_NONSTOP_TSC is not advertised in certain cases, i.e.
all AMD and some old Intel processors. In which case TSC would need to
be restored on CPU from platform time by Xen upon exiting C-states.

As platform time might be behind the last TSC stamp recorded for the
current CPU, invariant of TSC stamp being always behind local TSC counter
is violated. This has an effect of get_s_time() going negative resulting
in eventual system hang or crash.

Fix this issue by updating local TSC stamp along with TSC counter write.

Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index e79cb4d019837d7f244bb15197447a5d70cd0582..f6b26f88833bebd9bed23f67aadd46925f649f97 100644 (file)
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -955,10 +955,16 @@ u64 stime2tsc(s_time_t stime)
 
 void cstate_restore_tsc(void)
 {
+    struct cpu_time *t = &this_cpu(cpu_time);
+
     if ( boot_cpu_has(X86_FEATURE_NONSTOP_TSC) )
         return;
 
-    write_tsc(stime2tsc(read_platform_stime(NULL)));
+    t->stamp.master_stime = read_platform_stime(NULL);
+    t->stamp.local_tsc = stime2tsc(t->stamp.master_stime);
+    t->stamp.local_stime = t->stamp.master_stime;
+
+    write_tsc(t->stamp.local_tsc);
 }
 
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