On 20/05/16 16:10, Julien Grall wrote:
> Hi Juergen,
>
> On 20/05/16 14:22, Juergen Gross wrote:
>> A guest mapping vcpu_runstate_info into its memory can't read this
>> information from another cpu but the one the data is referring to.
>> Reason is there is no reliable way for the guest to detect a concurrent
>> data update by the hypervisor.
>>
>> This patch series adds an update flag to the mapped data which can be
>> used by the guest to detect an update is occurring. As this flag is
>> modifying the current interface it has to be activated by using a
>> vm_assist hypercall, which in turn has to be made available for ARM.
>>
>> Runtime tested on x86 with a modified Linux kernel using the new
>> feature.
>> Compile tested only for ARM.
>
> I would like to give a go on ARM. Who it be possible to provide the
> patch for Linux and how to test it?
Sure. You'll need the four attached patches (to be applied on top of
kernel 4.6). With CONFIG_PARAVIRT_TIME_ACCOUNTING set in the kernel
config, full functionality will be used (without being set the runstate
info of other cpus won't be read).
You can verify the vm_assist hypercall has worked via "xl debug-keys q"
and "xl dmesg | grep vm_assist" (value should be 00000020 on ARM).
Juergen
>From 689b4ba8c13be73ed51e485a7f7baea593d0ce6e Mon Sep 17 00:00:00 2001
From: Juergen Gross <jgr...@suse.com>
Date: Tue, 17 May 2016 14:03:02 +0200
Subject: [PATCH v4] xen: add steal_clock support on x86
The pv_time_ops structure contains a function pointer for the
"steal_clock" functionality used only by KVM and Xen on ARM. Xen on x86
uses its own mechanism to account for the "stolen" time a thread wasn't
able to run due to hypervisor scheduling.
Add support in Xen arch independent time handling for this feature by
moving it out of the arm arch into drivers/xen and remove the x86 Xen
hack.
Signed-off-by: Juergen Gross <jgr...@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrov...@oracle.com>
---
V4: minor adjustments as requested by Stefano Stabellini (remove
no longer needed #include, remove __init from header)
V3: add #include <asm/paravirt.h> to avoid build error on arm
V2: remove the x86 do_stolen_accounting() hack
---
arch/arm/xen/enlighten.c | 18 ++----------------
arch/x86/xen/time.c | 44 ++------------------------------------------
drivers/xen/time.c | 20 ++++++++++++++++++++
include/linux/kernel_stat.h | 1 -
include/xen/xen-ops.h | 1 +
kernel/sched/cputime.c | 10 ----------
6 files changed, 25 insertions(+), 69 deletions(-)
diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index 75cd734..71db30c 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -12,7 +12,6 @@
#include <xen/page.h>
#include <xen/interface/sched.h>
#include <xen/xen-ops.h>
-#include <asm/paravirt.h>
#include <asm/xen/hypervisor.h>
#include <asm/xen/hypercall.h>
#include <asm/system_misc.h>
@@ -84,19 +83,6 @@ int xen_unmap_domain_gfn_range(struct vm_area_struct *vma,
}
EXPORT_SYMBOL_GPL(xen_unmap_domain_gfn_range);
-static unsigned long long xen_stolen_accounting(int cpu)
-{
- struct vcpu_runstate_info state;
-
- BUG_ON(cpu != smp_processor_id());
-
- xen_get_runstate_snapshot(&state);
-
- WARN_ON(state.state != RUNSTATE_running);
-
- return state.time[RUNSTATE_runnable] + state.time[RUNSTATE_offline];
-}
-
static void xen_read_wallclock(struct timespec64 *ts)
{
u32 version;
@@ -355,8 +341,8 @@ static int __init xen_guest_init(void)
register_cpu_notifier(&xen_cpu_notifier);
- pv_time_ops.steal_clock = xen_stolen_accounting;
- static_key_slow_inc(¶virt_steal_enabled);
+ xen_time_setup_guest();
+
if (xen_initial_domain())
pvclock_gtod_register_notifier(&xen_pvclock_gtod_notifier);
diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index a0a4e55..6be31df 100644
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -11,8 +11,6 @@
#include <linux/interrupt.h>
#include <linux/clocksource.h>
#include <linux/clockchips.h>
-#include <linux/kernel_stat.h>
-#include <linux/math64.h>
#include <linux/gfp.h>
#include <linux/slab.h>
#include <linux/pvclock_gtod.h>
@@ -31,44 +29,6 @@
/* Xen may fire a timer up to this many ns early */
#define TIMER_SLOP 100000
-#define NS_PER_TICK (1000000000LL / HZ)
-
-/* snapshots of runstate info */
-static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate_snapshot);
-
-/* unused ns of stolen time */
-static DEFINE_PER_CPU(u64, xen_residual_stolen);
-
-static void do_stolen_accounting(void)
-{
- struct vcpu_runstate_info state;
- struct vcpu_runstate_info *snap;
- s64 runnable, offline, stolen;
- cputime_t ticks;
-
- xen_get_runstate_snapshot(&state);
-
- WARN_ON(state.state != RUNSTATE_running);
-
- snap = this_cpu_ptr(&xen_runstate_snapshot);
-
- /* work out how much time the VCPU has not been runn*ing* */
- runnable = state.time[RUNSTATE_runnable] -
snap->time[RUNSTATE_runnable];
- offline = state.time[RUNSTATE_offline] - snap->time[RUNSTATE_offline];
-
- *snap = state;
-
- /* Add the appropriate number of ticks of stolen time,
- including any left-overs from last time. */
- stolen = runnable + offline + __this_cpu_read(xen_residual_stolen);
-
- if (stolen < 0)
- stolen = 0;
-
- ticks = iter_div_u64_rem(stolen, NS_PER_TICK, &stolen);
- __this_cpu_write(xen_residual_stolen, stolen);
- account_steal_ticks(ticks);
-}
/* Get the TSC speed from Xen */
static unsigned long xen_tsc_khz(void)
@@ -335,8 +295,6 @@ static irqreturn_t xen_timer_interrupt(int irq, void
*dev_id)
ret = IRQ_HANDLED;
}
- do_stolen_accounting();
-
return ret;
}
@@ -431,6 +389,8 @@ static void __init xen_time_init(void)
xen_setup_timer(cpu);
xen_setup_cpu_clockevents();
+ xen_time_setup_guest();
+
if (xen_initial_domain())
pvclock_gtod_register_notifier(&xen_pvclock_gtod_notifier);
}
diff --git a/drivers/xen/time.c b/drivers/xen/time.c
index 7107842..2257b66 100644
--- a/drivers/xen/time.c
+++ b/drivers/xen/time.c
@@ -6,6 +6,7 @@
#include <linux/math64.h>
#include <linux/gfp.h>
+#include <asm/paravirt.h>
#include <asm/xen/hypervisor.h>
#include <asm/xen/hypercall.h>
@@ -75,6 +76,15 @@ bool xen_vcpu_stolen(int vcpu)
return per_cpu(xen_runstate, vcpu).state == RUNSTATE_runnable;
}
+static u64 xen_steal_clock(int cpu)
+{
+ struct vcpu_runstate_info state;
+
+ BUG_ON(cpu != smp_processor_id());
+ xen_get_runstate_snapshot(&state);
+ return state.time[RUNSTATE_runnable] + state.time[RUNSTATE_offline];
+}
+
void xen_setup_runstate_info(int cpu)
{
struct vcpu_register_runstate_memory_area area;
@@ -86,3 +96,13 @@ void xen_setup_runstate_info(int cpu)
BUG();
}
+void __init xen_time_setup_guest(void)
+{
+ pv_time_ops.steal_clock = xen_steal_clock;
+
+ static_key_slow_inc(¶virt_steal_enabled);
+ /*
+ * We can't set paravirt_steal_rq_enabled as this would require the
+ * capability to read another cpu's runstate info.
+ */
+}
diff --git a/include/linux/kernel_stat.h b/include/linux/kernel_stat.h
index 25a822f..44fda64 100644
--- a/include/linux/kernel_stat.h
+++ b/include/linux/kernel_stat.h
@@ -92,7 +92,6 @@ static inline void account_process_tick(struct task_struct
*tsk, int user)
extern void account_process_tick(struct task_struct *, int user);
#endif
-extern void account_steal_ticks(unsigned long ticks);
extern void account_idle_ticks(unsigned long ticks);
#endif /* _LINUX_KERNEL_STAT_H */
diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
index 86abe07..77bf9d1 100644
--- a/include/xen/xen-ops.h
+++ b/include/xen/xen-ops.h
@@ -21,6 +21,7 @@ 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_get_runstate_snapshot(struct vcpu_runstate_info *res);
int xen_setup_shutdown_event(void);
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 75f98c5..8c4c6dc 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -490,16 +490,6 @@ void account_process_tick(struct task_struct *p, int
user_tick)
}
/*
- * Account multiple ticks of steal time.
- * @p: the process from which the cpu time has been stolen
- * @ticks: number of stolen ticks
- */
-void account_steal_ticks(unsigned long ticks)
-{
- account_steal_time(jiffies_to_cputime(ticks));
-}
-
-/*
* Account multiple ticks of idle time.
* @ticks: number of stolen ticks
*/
--
2.6.6
>From 4073bb301aed18981ec69c3cf5f0df4fae567d7c Mon Sep 17 00:00:00 2001
From: Juergen Gross <jgr...@suse.com>
Date: Fri, 20 May 2016 09:32:30 +0200
Subject: [PATCH 1/3] xen: update xen headers
Update some Xen headers to be able to use new functionality.
Signed-off-by: Juergen Gross <jgr...@suse.com>
---
include/xen/interface/vcpu.h | 24 +++++++++++++++---------
include/xen/interface/xen.h | 17 ++++++++++++++++-
2 files changed, 31 insertions(+), 10 deletions(-)
diff --git a/include/xen/interface/vcpu.h b/include/xen/interface/vcpu.h
index b05288c..98188c8 100644
--- a/include/xen/interface/vcpu.h
+++ b/include/xen/interface/vcpu.h
@@ -75,15 +75,21 @@
*/
#define VCPUOP_get_runstate_info 4
struct vcpu_runstate_info {
- /* VCPU's current state (RUNSTATE_*). */
- int state;
- /* When was current state entered (system time, ns)? */
- uint64_t state_entry_time;
- /*
- * Time spent in each RUNSTATE_* (ns). The sum of these times is
- * guaranteed not to drift from system time.
- */
- uint64_t time[4];
+ /* VCPU's current state (RUNSTATE_*). */
+ int state;
+ /* When was current state entered (system time, ns)? */
+ uint64_t state_entry_time;
+ /*
+ * Update indicator set in state_entry_time:
+ * When activated via VMASST_TYPE_runstate_update_flag, set during
+ * updates in guest memory mapped copy of vcpu_runstate_info.
+ */
+#define XEN_RUNSTATE_UPDATE (1ULL << 63)
+ /*
+ * Time spent in each RUNSTATE_* (ns). The sum of these times is
+ * guaranteed not to drift from system time.
+ */
+ uint64_t time[4];
};
DEFINE_GUEST_HANDLE_STRUCT(vcpu_runstate_info);
diff --git a/include/xen/interface/xen.h b/include/xen/interface/xen.h
index d133112..1b0d189 100644
--- a/include/xen/interface/xen.h
+++ b/include/xen/interface/xen.h
@@ -413,7 +413,22 @@ DEFINE_GUEST_HANDLE_STRUCT(mmuext_op);
/* x86/PAE guests: support PDPTs above 4GB. */
#define VMASST_TYPE_pae_extended_cr3 3
-#define MAX_VMASST_TYPE 3
+/*
+ * x86 guests: Sane behaviour for virtual iopl
+ * - virtual iopl updated from do_iret() hypercalls.
+ * - virtual iopl reported in bounce frames.
+ * - guest kernels assumed to be level 0 for the purpose of iopl checks.
+ */
+#define VMASST_TYPE_architectural_iopl 4
+
+/*
+ * All guests: activate update indicator in vcpu_runstate_info
+ * Enable setting the XEN_RUNSTATE_UPDATE flag in guest memory mapped
+ * vcpu_runstate_info during updates of the runstate information.
+ */
+#define VMASST_TYPE_runstate_update_flag 5
+
+#define MAX_VMASST_TYPE 5
#ifndef __ASSEMBLY__
--
2.6.6
>From ab457b88c03a66c6051ac022b51bc5c218f48842 Mon Sep 17 00:00:00 2001
From: Juergen Gross <jgr...@suse.com>
Date: Fri, 20 May 2016 12:08:21 +0200
Subject: [PATCH 2/3] arm/xen: add support for vm_assist hypercall
Add support for the Xen HYPERVISOR_vm_assist hypercall.
Signed-off-by: Juergen Gross <jgr...@suse.com>
---
arch/arm/include/asm/xen/hypercall.h | 1 +
arch/arm/xen/enlighten.c | 1 +
arch/arm/xen/hypercall.S | 1 +
arch/arm64/xen/hypercall.S | 1 +
4 files changed, 4 insertions(+)
diff --git a/arch/arm/include/asm/xen/hypercall.h
b/arch/arm/include/asm/xen/hypercall.h
index b6b962d..9d874db 100644
--- a/arch/arm/include/asm/xen/hypercall.h
+++ b/arch/arm/include/asm/xen/hypercall.h
@@ -52,6 +52,7 @@ int HYPERVISOR_memory_op(unsigned int cmd, void *arg);
int HYPERVISOR_physdev_op(int cmd, void *arg);
int HYPERVISOR_vcpu_op(int cmd, int vcpuid, void *extra_args);
int HYPERVISOR_tmem_op(void *arg);
+int HYPERVISOR_vm_assist(unsigned int cmd, unsigned int type);
int HYPERVISOR_platform_op_raw(void *arg);
static inline int HYPERVISOR_platform_op(struct xen_platform_op *op)
{
diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index 71db30c..0f3aa12 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -389,4 +389,5 @@ EXPORT_SYMBOL_GPL(HYPERVISOR_vcpu_op);
EXPORT_SYMBOL_GPL(HYPERVISOR_tmem_op);
EXPORT_SYMBOL_GPL(HYPERVISOR_platform_op);
EXPORT_SYMBOL_GPL(HYPERVISOR_multicall);
+EXPORT_SYMBOL_GPL(HYPERVISOR_vm_assist);
EXPORT_SYMBOL_GPL(privcmd_call);
diff --git a/arch/arm/xen/hypercall.S b/arch/arm/xen/hypercall.S
index 9a36f4f..a648dfc 100644
--- a/arch/arm/xen/hypercall.S
+++ b/arch/arm/xen/hypercall.S
@@ -91,6 +91,7 @@ HYPERCALL3(vcpu_op);
HYPERCALL1(tmem_op);
HYPERCALL1(platform_op_raw);
HYPERCALL2(multicall);
+HYPERCALL2(vm_assist);
ENTRY(privcmd_call)
stmdb sp!, {r4}
diff --git a/arch/arm64/xen/hypercall.S b/arch/arm64/xen/hypercall.S
index 70df80e..329c802 100644
--- a/arch/arm64/xen/hypercall.S
+++ b/arch/arm64/xen/hypercall.S
@@ -82,6 +82,7 @@ HYPERCALL3(vcpu_op);
HYPERCALL1(tmem_op);
HYPERCALL1(platform_op_raw);
HYPERCALL2(multicall);
+HYPERCALL2(vm_assist);
ENTRY(privcmd_call)
mov x16, x0
--
2.6.6
>From f27da1aba6c9c92add4f88b4dcec517e5e321caa Mon Sep 17 00:00:00 2001
From: Juergen Gross <jgr...@suse.com>
Date: Fri, 20 May 2016 12:25:58 +0200
Subject: [PATCH 3/3] xen: support runqueue steal time on xen
Up to now reading the stolen time of a remote cpu was not possible in a
performant way under Xen. This made support of runqueue steal time via
paravirt_steal_rq_enabled impossible.
With the addition of an appropriate hypervisor interface this is now
possible, so add the support.
Signed-off-by: Juergen Gross <jgr...@suse.com>
---
drivers/xen/time.c | 42 +++++++++++++++++++++++++-----------------
1 file changed, 25 insertions(+), 17 deletions(-)
diff --git a/drivers/xen/time.c b/drivers/xen/time.c
index 2257b66..04b6cb7 100644
--- a/drivers/xen/time.c
+++ b/drivers/xen/time.c
@@ -19,6 +19,9 @@
/* runstate info updated by Xen */
static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate);
+/* runstate info of remote cpu accessible */
+static bool xen_runstate_remote;
+
/* return an consistent snapshot of 64-bit time/counter value */
static u64 get64(const u64 *p)
{
@@ -47,27 +50,31 @@ static u64 get64(const u64 *p)
return ret;
}
-/*
- * Runstate accounting
- */
-void xen_get_runstate_snapshot(struct vcpu_runstate_info *res)
+static void xen_get_runstate_snapshot_cpu(struct vcpu_runstate_info *res,
+ unsigned cpu)
{
u64 state_time;
struct vcpu_runstate_info *state;
BUG_ON(preemptible());
- state = this_cpu_ptr(&xen_runstate);
+ state = per_cpu_ptr(&xen_runstate, cpu);
- /*
- * The runstate info is always updated by the hypervisor on
- * the current CPU, so there's no need to use anything
- * stronger than a compiler barrier when fetching it.
- */
do {
state_time = get64(&state->state_entry_time);
+ rmb();
*res = READ_ONCE(*state);
- } while (get64(&state->state_entry_time) != state_time);
+ rmb();
+ } while (get64(&state->state_entry_time) != state_time ||
+ (state_time & XEN_RUNSTATE_UPDATE));
+}
+
+/*
+ * Runstate accounting
+ */
+void xen_get_runstate_snapshot(struct vcpu_runstate_info *res)
+{
+ xen_get_runstate_snapshot_cpu(res, smp_processor_id());
}
/* return true when a vcpu could run but has no real cpu to run on */
@@ -80,8 +87,8 @@ static u64 xen_steal_clock(int cpu)
{
struct vcpu_runstate_info state;
- BUG_ON(cpu != smp_processor_id());
- xen_get_runstate_snapshot(&state);
+ BUG_ON(!xen_runstate_remote && cpu != smp_processor_id());
+ xen_get_runstate_snapshot_cpu(&state, cpu);
return state.time[RUNSTATE_runnable] + state.time[RUNSTATE_offline];
}
@@ -98,11 +105,12 @@ void xen_setup_runstate_info(int cpu)
void __init xen_time_setup_guest(void)
{
+ xen_runstate_remote = !HYPERVISOR_vm_assist(VMASST_CMD_enable,
+ VMASST_TYPE_runstate_update_flag);
+
pv_time_ops.steal_clock = xen_steal_clock;
static_key_slow_inc(¶virt_steal_enabled);
- /*
- * We can't set paravirt_steal_rq_enabled as this would require the
- * capability to read another cpu's runstate info.
- */
+ if (xen_runstate_remote)
+ static_key_slow_inc(¶virt_steal_rq_enabled);
}
--
2.6.6
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