From bbf283f853f8c0e4d29248dd44d3b0e0abc07629 Mon Sep 17 00:00:00 2001 From: Igor Druzhinin Date: Fri, 17 Jan 2020 16:11:20 +0100 Subject: [PATCH] x86/time: update TSC stamp on restore from deep C-state MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Reviewed-by: Roger Pau Monné Acked-by: Jan Beulich --- 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 e79cb4d019..f6b26f8883 100644 --- 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); } /*************************************************************************** -- 2.30.2