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Subject[PATCH v2] xen: Fix x86 sched_clock() interface for xen
Date
Commit f94c8d11699759 ("sched/clock, x86/tsc: Rework the x86 'unstable'
sched_clock() interface") broke Xen guest time handling across
migration:

[ 187.249951] Freezing user space processes ... (elapsed 0.001 seconds) done.
[ 187.251137] OOM killer disabled.
[ 187.251137] Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
[ 187.252299] suspending xenstore...
[ 187.266987] xen:grant_table: Grant tables using version 1 layout
[18446743811.706476] OOM killer enabled.
[18446743811.706478] Restarting tasks ... done.
[18446743811.720505] Setting capacity to 16777216

Fix that by setting xen_sched_clock_offset at resume time to ensure a
monotonic clock value.

Fixes: f94c8d11699759 ("sched/clock, x86/tsc: Rework the x86 'unstable' sched_clock() interface")
Cc: <stable@vger.kernel.org> # 4.11
Reported-by: Hans van Kranenburg <hans@knorrie.org>
Signed-off-by: Juergen Gross <jgross@suse.com>
---
arch/x86/xen/time.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index 72bf446c3fee..3c1dfdf26284 100644
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -379,12 +379,15 @@ static const struct pv_time_ops xen_time_ops __initconst = {
};

static struct pvclock_vsyscall_time_info *xen_clock __read_mostly;
+static u64 xen_clock_value_saved;

void xen_save_time_memory_area(void)
{
struct vcpu_register_time_memory_area t;
int ret;

+ xen_clock_value_saved = xen_clocksource_read() - xen_sched_clock_offset;
+
if (!xen_clock)
return;

@@ -404,7 +407,7 @@ void xen_restore_time_memory_area(void)
int ret;

if (!xen_clock)
- return;
+ goto out;

t.addr.v = &xen_clock->pvti;

@@ -421,6 +424,11 @@ void xen_restore_time_memory_area(void)
if (ret != 0)
pr_notice("Cannot restore secondary vcpu_time_info (err %d)",
ret);
+
+out:
+ /* Need pvclock_resume() before using xen_clocksource_read(). */
+ pvclock_resume();
+ xen_sched_clock_offset = xen_clocksource_read() - xen_clock_value_saved;
}

static void xen_setup_vsyscall_time_info(void)
--
2.16.4
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