[Xen-changelog] [xen stable-4.12] x86/time: update TSC stamp on restore from deep C-state

[patchbot@xxxxxxx]

commit a12589ffc27ee144b5be9ba95dd498e2d719fa5e
Author:     Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
AuthorDate: Thu Mar 5 11:14:38 2020 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Mar 5 11:14:38 2020 +0100

    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@xxxxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: bbf283f853f8c0e4d29248dd44d3b0e0abc07629
    master date: 2020-01-17 16:11:20 +0100
---
 xen/arch/x86/time.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index 50219c515a..09692bcdb7 100644
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -857,10 +857,16 @@ 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);
 }
 
 /***************************************************************************
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.12

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