Commit-ID: 27c634054a3155e1d9a02f0e362e4f4ff8d28ee7 Gitweb: http://git.kernel.org/tip/27c634054a3155e1d9a02f0e362e4f4ff8d28ee7 Author: Andy Lutomirski <luto@xxxxxxxxxx> AuthorDate: Thu, 25 Jun 2015 18:44:10 +0200 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitDate: Mon, 6 Jul 2015 15:23:29 +0200 x86/asm/tsc: Use rdtsc_ordered() in read_tsc() instead of get_cycles() There are two logical changes here. First, this removes a check for cpu_has_tsc. That check is unnecessary, as we don't register the TSC as a clocksource on systems that have no TSC. Second, it adds a barrier, thus preventing observable non-monotonicity. I suspect that the missing barrier was never a problem in practice because system calls themselves were heavy enough barriers to prevent user code from observing time warps due to speculation. (Without the corresponding barrier in the vDSO, however, non-monotonicity is easy to detect.) Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Brian Gerst <brgerst@xxxxxxxxx> Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx> Cc: H. Peter Anvin <hpa@xxxxxxxxx> Cc: Huang Rui <ray.huang@xxxxxxx> Cc: John Stultz <john.stultz@xxxxxxxxxx> Cc: Len Brown <lenb@xxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: kvm ML <kvm@xxxxxxxxxxxxxxx> Link: http://lkml.kernel.org/r/c6ff621a053127a65b70f175443578db7a0711be.1434501121.git.luto@xxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> --- arch/x86/kernel/tsc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 21d6e04..451bade0 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -961,7 +961,7 @@ static struct clocksource clocksource_tsc; */ static cycle_t read_tsc(struct clocksource *cs) { - return (cycle_t)get_cycles(); + return (cycle_t)rdtsc_ordered(); } /* -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
