[linux] 01/01: xen/time: do not decrease steal time after live migration on xen
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carnil pushed a commit to branch stretch
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commit 66864f726855f0a37ac857478507980cddbde017
Author: Salvatore Bonaccorso <carnil at debian.org>
Date: Sun Dec 3 10:51:49 2017 +0100
xen/time: do not decrease steal time after live migration on xen
Closes: #871608
---
debian/changelog | 7 +
...-not-decrease-steal-time-after-live-migra.patch | 200 +++++++++++++++++++++
debian/patches/series | 1 +
3 files changed, 208 insertions(+)
diff --git a/debian/changelog b/debian/changelog
index 82ef489..9c96c74 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,3 +1,10 @@
+linux (4.9.65-3) UNRELEASED; urgency=medium
+
+ * xen/time: do not decrease steal time after live migration on xen
+ (Closes: #871608)
+
+ -- Salvatore Bonaccorso <carnil at debian.org> Sun, 03 Dec 2017 20:38:22 +0100
+
linux (4.9.65-2) stretch; urgency=medium
* [s390x] qeth: Ignore ABI changes (fixes FTBFS)
diff --git a/debian/patches/bugfix/all/xen-time-do-not-decrease-steal-time-after-live-migra.patch b/debian/patches/bugfix/all/xen-time-do-not-decrease-steal-time-after-live-migra.patch
new file mode 100644
index 0000000..b5382d0
--- /dev/null
+++ b/debian/patches/bugfix/all/xen-time-do-not-decrease-steal-time-after-live-migra.patch
@@ -0,0 +1,200 @@
+From: Dongli Zhang <dongli.zhang at oracle.com>
+Date: Wed, 1 Nov 2017 09:46:33 +0800
+Subject: xen/time: do not decrease steal time after live migration on xen
+Origin: https://git.kernel.org/linus/5e25f5db6abb96ca8ee2aaedcb863daa6dfcc07a
+Bug-Debian: https://bugs.debian.org/871608
+
+After guest live migration on xen, steal time in /proc/stat
+(cpustat[CPUTIME_STEAL]) might decrease because steal returned by
+xen_steal_lock() might be less than this_rq()->prev_steal_time which is
+derived from previous return value of xen_steal_clock().
+
+For instance, steal time of each vcpu is 335 before live migration.
+
+cpu 198 0 368 200064 1962 0 0 1340 0 0
+cpu0 38 0 81 50063 492 0 0 335 0 0
+cpu1 65 0 97 49763 634 0 0 335 0 0
+cpu2 38 0 81 50098 462 0 0 335 0 0
+cpu3 56 0 107 50138 374 0 0 335 0 0
+
+After live migration, steal time is reduced to 312.
+
+cpu 200 0 370 200330 1971 0 0 1248 0 0
+cpu0 38 0 82 50123 500 0 0 312 0 0
+cpu1 65 0 97 49832 634 0 0 312 0 0
+cpu2 39 0 82 50167 462 0 0 312 0 0
+cpu3 56 0 107 50207 374 0 0 312 0 0
+
+Since runstate times are cumulative and cleared during xen live migration
+by xen hypervisor, the idea of this patch is to accumulate runstate times
+to global percpu variables before live migration suspend. Once guest VM is
+resumed, xen_get_runstate_snapshot_cpu() would always return the sum of new
+runstate times and previously accumulated times stored in global percpu
+variables.
+
+Comment above HYPERVISOR_suspend() has been removed as it is inaccurate:
+the call can return an error code (e.g., possibly -EPERM in the future).
+
+Similar and more severe issue would impact prior linux 4.8-4.10 as
+discussed by Michael Las at
+https://0xstubs.org/debugging-a-flaky-cpu-steal-time-counter-on-a-paravirtualized-xen-guest,
+which would overflow steal time and lead to 100% st usage in top command
+for linux 4.8-4.10. A backport of this patch would fix that issue.
+
+[boris: added linux/slab.h to driver/xen/time.c, slightly reformatted
+ commit message]
+
+References: https://0xstubs.org/debugging-a-flaky-cpu-steal-time-counter-on-a-paravirtualized-xen-guest
+Signed-off-by: Dongli Zhang <dongli.zhang at oracle.com>
+Reviewed-by: Boris Ostrovsky <boris.ostrovsky at oracle.com>
+Signed-off-by: Boris Ostrovsky <boris.ostrovsky at oracle.com>
+---
+ drivers/xen/manage.c | 7 ++---
+ drivers/xen/time.c | 72 +++++++++++++++++++++++++++++++++++++++++++++++++--
+ include/xen/xen-ops.h | 1 +
+ 3 files changed, 73 insertions(+), 7 deletions(-)
+
+diff --git a/drivers/xen/manage.c b/drivers/xen/manage.c
+index c425d03d37d2..8835065029d3 100644
+--- a/drivers/xen/manage.c
++++ b/drivers/xen/manage.c
+@@ -72,18 +72,15 @@ static int xen_suspend(void *data)
+ }
+
+ gnttab_suspend();
++ xen_manage_runstate_time(-1);
+ xen_arch_pre_suspend();
+
+- /*
+- * This hypercall returns 1 if suspend was cancelled
+- * or the domain was merely checkpointed, and 0 if it
+- * is resuming in a new domain.
+- */
+ si->cancelled = HYPERVISOR_suspend(xen_pv_domain()
+ ? virt_to_gfn(xen_start_info)
+ : 0);
+
+ xen_arch_post_suspend(si->cancelled);
++ xen_manage_runstate_time(si->cancelled ? 1 : 0);
+ gnttab_resume();
+
+ if (!si->cancelled) {
+diff --git a/drivers/xen/time.c b/drivers/xen/time.c
+index ac5f23fcafc2..8c46f555d82a 100644
+--- a/drivers/xen/time.c
++++ b/drivers/xen/time.c
+@@ -5,6 +5,7 @@
+ #include <linux/kernel_stat.h>
+ #include <linux/math64.h>
+ #include <linux/gfp.h>
++#include <linux/slab.h>
+
+ #include <asm/paravirt.h>
+ #include <asm/xen/hypervisor.h>
+@@ -19,6 +20,8 @@
+ /* runstate info updated by Xen */
+ static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate);
+
++static DEFINE_PER_CPU(u64[4], old_runstate_time);
++
+ /* return an consistent snapshot of 64-bit time/counter value */
+ static u64 get64(const u64 *p)
+ {
+@@ -47,8 +50,8 @@ static u64 get64(const u64 *p)
+ return ret;
+ }
+
+-static void xen_get_runstate_snapshot_cpu(struct vcpu_runstate_info *res,
+- unsigned int cpu)
++static void xen_get_runstate_snapshot_cpu_delta(
++ struct vcpu_runstate_info *res, unsigned int cpu)
+ {
+ u64 state_time;
+ struct vcpu_runstate_info *state;
+@@ -66,6 +69,71 @@ static void xen_get_runstate_snapshot_cpu(struct vcpu_runstate_info *res,
+ (state_time & XEN_RUNSTATE_UPDATE));
+ }
+
++static void xen_get_runstate_snapshot_cpu(struct vcpu_runstate_info *res,
++ unsigned int cpu)
++{
++ int i;
++
++ xen_get_runstate_snapshot_cpu_delta(res, cpu);
++
++ for (i = 0; i < 4; i++)
++ res->time[i] += per_cpu(old_runstate_time, cpu)[i];
++}
++
++void xen_manage_runstate_time(int action)
++{
++ static struct vcpu_runstate_info *runstate_delta;
++ struct vcpu_runstate_info state;
++ int cpu, i;
++
++ switch (action) {
++ case -1: /* backup runstate time before suspend */
++ if (unlikely(runstate_delta))
++ pr_warn_once("%s: memory leak as runstate_delta is not NULL\n",
++ __func__);
++
++ runstate_delta = kmalloc_array(num_possible_cpus(),
++ sizeof(*runstate_delta),
++ GFP_ATOMIC);
++ if (unlikely(!runstate_delta)) {
++ pr_warn("%s: failed to allocate runstate_delta\n",
++ __func__);
++ return;
++ }
++
++ for_each_possible_cpu(cpu) {
++ xen_get_runstate_snapshot_cpu_delta(&state, cpu);
++ memcpy(runstate_delta[cpu].time, state.time,
++ sizeof(runstate_delta[cpu].time));
++ }
++
++ break;
++
++ case 0: /* backup runstate time after resume */
++ if (unlikely(!runstate_delta)) {
++ pr_warn("%s: cannot accumulate runstate time as runstate_delta is NULL\n",
++ __func__);
++ return;
++ }
++
++ for_each_possible_cpu(cpu) {
++ for (i = 0; i < 4; i++)
++ per_cpu(old_runstate_time, cpu)[i] +=
++ runstate_delta[cpu].time[i];
++ }
++
++ break;
++
++ default: /* do not accumulate runstate time for checkpointing */
++ break;
++ }
++
++ if (action != -1 && runstate_delta) {
++ kfree(runstate_delta);
++ runstate_delta = NULL;
++ }
++}
++
+ /*
+ * Runstate accounting
+ */
+diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
+index 218e6aae5433..09072271f122 100644
+--- a/include/xen/xen-ops.h
++++ b/include/xen/xen-ops.h
+@@ -32,6 +32,7 @@ void xen_resume_notifier_unregister(struct notifier_block *nb);
+ bool xen_vcpu_stolen(int vcpu);
+ void xen_setup_runstate_info(int cpu);
+ void xen_time_setup_guest(void);
++void xen_manage_runstate_time(int action);
+ void xen_get_runstate_snapshot(struct vcpu_runstate_info *res);
+ u64 xen_steal_clock(int cpu);
+
+--
+2.15.1
+
diff --git a/debian/patches/series b/debian/patches/series
index 265c6c0..4490933 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -102,6 +102,7 @@ bugfix/all/mm-mmap.c-do-not-blow-on-prot_none-map_fixed-holes-i.patch
bugfix/all/mm-mmap.c-expand_downwards-don-t-require-the-gap-if-.patch
bugfix/x86/mmap-remember-the-map_fixed-flag-as-vm_fixed.patch
bugfix/x86/mmap-add-an-exception-to-the-stack-gap-for-hotspot-jvm.patch
+bugfix/all/xen-time-do-not-decrease-steal-time-after-live-migra.patch
# Miscellaneous features
features/all/netfilter-nft_ct-add-notrack-support.patch
--
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