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>
master commit: bbf283f853f8c0e4d29248dd44d3b0e0abc07629
master date: 2020-01-17 16:11:20 +0100

diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index 430fba1e66b04ec6524af8f0b34a39ed1b9011b5..373b10b6dc7552a148142aaae1ee82fec61e0a70 100644 (file)
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -854,10 +854,16 @@ 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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