Attachment 941545 Details for Bug 1145751 – RHEL PATCH 6/6

[patch] RHEL PATCH 6/6

0006-clocksource-Move-cycle_last-validation-to-core-code.patch (text/plain), 4.69 KB, created by Prarit Bhargava on 2014-09-26 11:29:15 UTC

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Creator: Prarit Bhargava

Created: 2014-09-26 11:29:15 UTC

Size: 4.69 KB

patch

obsolete

>From 2163cae51104f2303af59fe294defe2e1d6665c4 Mon Sep 17 00:00:00 2001
>From: Prarit Bhargava <prarit@redhat.com>
>Date: Thu, 25 Sep 2014 11:46:49 -0400
>Subject: [6/6] clocksource: Move cycle_last validation to core code
>
>Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1145751
>
>commit 09ec54429c6d10f87d1f084de53ae2c1c3a81108
>Author: Thomas Gleixner <tglx@linutronix.de>
>Date:   Wed Jul 16 21:05:12 2014 +0000
>
>    clocksource: Move cycle_last validation to core code
>
>    The only user of the cycle_last validation is the x86 TSC. In order to
>    provide NMI safe accessor functions for clock monotonic and
>    monotonic_raw we need to do that in the core.
>
>    We can't do the TSC specific
>
>        if (now < cycle_last)
>           	    now = cycle_last;
>
>    for the other wrapping around clocksources, but TSC has
>    CLOCKSOURCE_MASK(64) which actually does not mask out anything so if
>    now is less than cycle_last the subtraction will give a negative
>    result. So we can check for that in clocksource_delta() and return 0
>    for that case.
>
>    Implement and enable it for x86
>
>    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>    Signed-off-by: John Stultz <john.stultz@linaro.org>
>---
> arch/x86/Kconfig                   |    1 +
> arch/x86/kernel/tsc.c              |   21 +++++++++------------
> kernel/time/Kconfig                |    5 +++++
> kernel/time/timekeeping_internal.h |    9 +++++++++
> 4 files changed, 24 insertions(+), 12 deletions(-)
>
>diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>index fdde1bc..4da05a9 100644
>--- a/arch/x86/Kconfig
>+++ b/arch/x86/Kconfig
>@@ -105,6 +105,7 @@ config X86
> 	select GENERIC_CMOS_UPDATE
> 	select GENERIC_CLOCKEVENTS
> 	select ARCH_CLOCKSOURCE_DATA if X86_64
>+	select CLOCKSOURCE_VALIDATE_LAST_CYCLE
> 	select GENERIC_CLOCKEVENTS_BROADCAST if X86_64 || (X86_32 && X86_LOCAL_APIC)
> 	select GENERIC_TIME_VSYSCALL if X86_64
> 	select KTIME_SCALAR if X86_32
>diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
>index e8bb8ce..4b89423 100644
>--- a/arch/x86/kernel/tsc.c
>+++ b/arch/x86/kernel/tsc.c
>@@ -752,7 +752,7 @@ core_initcall(cpufreq_tsc);
> static struct clocksource clocksource_tsc;
> 
> /*
>- * We compare the TSC to the cycle_last value in the clocksource
>+ * We used to compare the TSC to the cycle_last value in the clocksource
>  * structure to avoid a nasty time-warp. This can be observed in a
>  * very small window right after one CPU updated cycle_last under
>  * xtime/vsyscall_gtod lock and the other CPU reads a TSC value which
>@@ -762,26 +762,23 @@ static struct clocksource clocksource_tsc;
>  * due to the unsigned delta calculation of the time keeping core
>  * code, which is necessary to support wrapping clocksources like pm
>  * timer.
>+ *
>+ * This sanity check is now done in the core timekeeping code.
>+ * checking the result of read_tsc() - cycle_last for being negative.
>+ * That works because CLOCKSOURCE_MASK(64) does not mask out any bit.
>  */
> static cycle_t read_tsc(struct clocksource *cs)
> {
>-	cycle_t ret = (cycle_t)get_cycles();
>-
>-	return ret >= clocksource_tsc.cycle_last ?
>-		ret : clocksource_tsc.cycle_last;
>-}
>-
>-static void resume_tsc(struct clocksource *cs)
>-{
>-	if (!boot_cpu_has(X86_FEATURE_NONSTOP_TSC_S3))
>-		clocksource_tsc.cycle_last = 0;
>+	return (cycle_t)get_cycles();
> }
> 
>+/*
>+ * .mask MUST be CLOCKSOURCE_MASK(64). See comment above read_tsc()
>+ */
> static struct clocksource clocksource_tsc = {
> 	.name                   = "tsc",
> 	.rating                 = 300,
> 	.read                   = read_tsc,
>-	.resume			= resume_tsc,
> 	.mask                   = CLOCKSOURCE_MASK(64),
> 	.flags                  = CLOCK_SOURCE_IS_CONTINUOUS |
> 				  CLOCK_SOURCE_MUST_VERIFY,
>diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
>index 747bbc7..32a5eec 100644
>--- a/kernel/time/Kconfig
>+++ b/kernel/time/Kconfig
>@@ -12,6 +12,11 @@ config CLOCKSOURCE_WATCHDOG
> config ARCH_CLOCKSOURCE_DATA
> 	bool
> 
>+# Clocksources require validation of the clocksource against the last
>+# cycle update - x86/TSC misfeature
>+config CLOCKSOURCE_VALIDATE_LAST_CYCLE
>+	bool
>+
> # Timekeeping vsyscall support
> config GENERIC_TIME_VSYSCALL
> 	bool
>diff --git a/kernel/time/timekeeping_internal.h b/kernel/time/timekeeping_internal.h
>index e613d8a..676947b 100644
>--- a/kernel/time/timekeeping_internal.h
>+++ b/kernel/time/timekeeping_internal.h
>@@ -6,9 +6,18 @@
> #include <linux/time.h>
> #include <linux/clocksource.h>
> 
>+#ifdef CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE
>+static inline cycle_t clocksource_delta(cycle_t now, cycle_t last, cycle_t mask)
>+{
>+	cycle_t ret = (now - last) & mask;
>+
>+	return (s64) ret > 0 ? ret : 0;
>+}
>+#else
> static inline cycle_t clocksource_delta(cycle_t now, cycle_t last, cycle_t mask)
> {
> 	return (now - last) & mask;
> }
>+#endif
> 
> #endif /* _TIMEKEEPING_INTERNAL_H */
>-- 
>1.7.9.3
>

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