[PATCH 0/5 V4] Avoid soft lockup message when KVM is stopped by host

[PATCH 0/5 V4] Avoid soft lockup message when KVM is stopped by host

[Eric B Munson]

Changes from V3:
Include CC's on patch 3
Drop clear flag ioctl and have the watchdog clear the flag when it is reset

Changes from V2:
A new kvm functions defined in kvm_para.h, the only change to pvclock is the
initial flag definition

Changes from V1:
(Thanks Marcelo)
Host code has all been moved to arch/x86/kvm/x86.c
KVM_PAUSE_GUEST was renamed to KVM_GUEST_PAUSED

When a guest kernel is stopped by the host hypervisor it can look like a soft
lockup to the guest kernel.  This false warning can mask later soft lockup
warnings which may be real.  This patch series adds a method for a host
hypervisor to communicate to a guest kernel that it is being stopped.  The
final patch in the series has the watchdog check this flag when it goes to
issue a soft lockup warning and skip the warning if the guest knows it was
stopped.

It was attempted to solve this in Qemu, but the side effects of saving and
restoring the clock and tsc for each vcpu put the wall clock of the guest behind
by the amount of time of the pause.  This forces a guest to have ntp running
in order to keep the wall clock accurate.

Cc: mingo@redhat.com
Cc: hpa@zytor.com
Cc: arnd@arndb.de
Cc: ryanh@linux.vnet.ibm.com
Cc: aliguori@us.ibm.com
Cc: mtosatti@redhat.com
Cc: jeremy.fitzhardinge@citrix.com
Cc: kvm@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org

Eric B Munson (5):
  Add flag to indicate that a vm was stopped by the host
  Add functions to check if the host has stopped the vm
  Add ioctl for KVM_GUEST_STOPPED
  Add generic stubs for kvm stop check functions
  Add check for suspended vm in softlockup detector

 arch/x86/include/asm/kvm_host.h    |    2 ++
 arch/x86/include/asm/kvm_para.h    |    1 +
 arch/x86/include/asm/pvclock-abi.h |    1 +
 arch/x86/kernel/kvmclock.c         |   21 +++++++++++++++++++++
 arch/x86/kvm/x86.c                 |   20 ++++++++++++++++++++
 include/asm-generic/kvm_para.h     |   14 ++++++++++++++
 include/linux/kvm.h                |    2 ++
 kernel/watchdog.c                  |   12 ++++++++++++
 8 files changed, 73 insertions(+), 0 deletions(-)
 create mode 100644 include/asm-generic/kvm_para.h

-- 
1.7.5.4

[PATCH 1/5 V4] Add flag to indicate that a vm was stopped by the host

[Eric B Munson]

This flag will be used to check if the vm was stopped by the host when a soft
lockup was detected.  The host will set the flag when it stops the guest.  On
resume, the guest will check this flag if a soft lockup is detected and skip
issuing the warning.

Signed-off-by: Eric B Munson <emunson@mgebm.net>
Cc: mingo@redhat.com
Cc: hpa@zytor.com
Cc: arnd@arndb.de
Cc: ryanh@linux.vnet.ibm.com
Cc: aliguori@us.ibm.com
Cc: mtosatti@redhat.com
Cc: jeremy.fitzhardinge@citrix.com
Cc: kvm@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
---
 arch/x86/include/asm/pvclock-abi.h |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/pvclock-abi.h b/arch/x86/include/asm/pvclock-abi.h
index 35f2d19..6167fd7 100644
--- a/arch/x86/include/asm/pvclock-abi.h
+++ b/arch/x86/include/asm/pvclock-abi.h
@@ -40,5 +40,6 @@ struct pvclock_wall_clock {
 } __attribute__((__packed__));
 
 #define PVCLOCK_TSC_STABLE_BIT	(1 << 0)
+#define PVCLOCK_GUEST_STOPPED	(1 << 1)
 #endif /* __ASSEMBLY__ */
 #endif /* _ASM_X86_PVCLOCK_ABI_H */
-- 
1.7.5.4

[PATCH 2/5 V4] Add functions to check if the host has stopped the vm

[Eric B Munson]

When a host stops or suspends a VM it will set a flag to show this.  The
watchdog will use these functions to determine if a softlockup is real, or the
result of a suspended VM.

Signed-off-by: Eric B Munson <emunson@mgebm.net>
Cc: mingo@redhat.com
Cc: hpa@zytor.com
Cc: arnd@arndb.de
Cc: ryanh@linux.vnet.ibm.com
Cc: aliguori@us.ibm.com
Cc: mtosatti@redhat.com
Cc: jeremy.fitzhardinge@citrix.com
Cc: kvm@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
---
 arch/x86/include/asm/kvm_para.h |    1 +
 arch/x86/kernel/kvmclock.c      |   21 +++++++++++++++++++++
 2 files changed, 22 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
index 734c376..e9d63a6 100644
--- a/arch/x86/include/asm/kvm_para.h
+++ b/arch/x86/include/asm/kvm_para.h
@@ -95,6 +95,7 @@ struct kvm_vcpu_pv_apf_data {
 extern void kvmclock_init(void);
 extern int kvm_register_clock(char *txt);
 
+bool kvm_check_and_clear_guest_paused(int cpu);
 
 /* This instruction is vmcall.  On non-VT architectures, it will generate a
  * trap that we will then rewrite to the appropriate instruction.
diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index 44842d7..f0c0599 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -22,6 +22,7 @@
 #include <asm/msr.h>
 #include <asm/apic.h>
 #include <linux/percpu.h>
+#include <linux/hardirq.h>
 
 #include <asm/x86_init.h>
 #include <asm/reboot.h>
@@ -114,6 +115,26 @@ static void kvm_get_preset_lpj(void)
 	preset_lpj = lpj;
 }
 
+bool kvm_check_and_clear_guest_paused(int cpu)
+{
+	bool ret = false;
+	struct pvclock_vcpu_time_info *src;
+
+	/*
+	 * per_cpu() is safe here because this function is only called from
+	 * timer functions where preemption is already disabled.
+	 */
+	WARN_ON(!in_atomic());
+	src = &per_cpu(hv_clock, cpu);
+	if ((src->flags & PVCLOCK_GUEST_STOPPED) != 0) {
+		src->flags = src->flags & (~PVCLOCK_GUEST_STOPPED);
+		ret = true;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(kvm_check_and_clear_guest_paused);
+
 static struct clocksource kvm_clock = {
 	.name = "kvm-clock",
 	.read = kvm_clock_get_cycles,
-- 
1.7.5.4

[PATCH 3/5 V4] Add ioctl for KVM_GUEST_STOPPED

[Eric B Munson]

Now that we have a flag that will tell the guest it was suspended, create an
interface for that communication using a KVM ioctl.

Signed-off-by: Eric B Munson <emunson@mgebm.net>

Cc: mingo@redhat.com
Cc: hpa@zytor.com
Cc: arnd@arndb.de
Cc: ryanh@linux.vnet.ibm.com
Cc: aliguori@us.ibm.com
Cc: mtosatti@redhat.com
Cc: jeremy.fitzhardinge@citrix.com
Cc: kvm@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
---
 arch/x86/include/asm/kvm_host.h |    2 ++
 arch/x86/kvm/x86.c              |   20 ++++++++++++++++++++
 include/linux/kvm.h             |    2 ++
 3 files changed, 24 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index b4973f4..beb94c6 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -672,6 +672,8 @@ int kvm_pv_mmu_op(struct kvm_vcpu *vcpu, unsigned long bytes,
 		  gpa_t addr, unsigned long *ret);
 u8 kvm_get_guest_memory_type(struct kvm_vcpu *vcpu, gfn_t gfn);
 
+int kvm_set_guest_paused(struct kvm_vcpu *vcpu);
+
 extern bool tdp_enabled;
 
 u64 vcpu_tsc_khz(struct kvm_vcpu *vcpu);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c38efd7..0127617 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3295,6 +3295,10 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 
 		goto out;
 	}
+	case KVM_GUEST_PAUSED: {
+		r = kvm_set_guest_paused(vcpu);
+		break;
+	}
 	default:
 		r = -EINVAL;
 	}
@@ -6117,6 +6121,22 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int reason,
 }
 EXPORT_SYMBOL_GPL(kvm_task_switch);
 
+/*
+ * kvm_set_guest_paused() indicates to the guest kernel that it has been
+ * stopped by the hypervisor.  This function will be called from the host only.
+ * EINVAL is returned when the host attempts to set the flag for a guest that
+ * does not support pv clocks.
+ */
+int kvm_set_guest_paused(struct kvm_vcpu *vcpu)
+{
+	struct pvclock_vcpu_time_info *src = &vcpu->arch.hv_clock;
+	if (!vcpu->arch.time_page)
+		return -EINVAL;
+	src->flags |= PVCLOCK_GUEST_STOPPED;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(kvm_set_guest_paused);
+
 int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
 				  struct kvm_sregs *sregs)
 {
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index c3892fc..15578a2 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -762,6 +762,8 @@ struct kvm_clock_data {
 #define KVM_CREATE_SPAPR_TCE	  _IOW(KVMIO,  0xa8, struct kvm_create_spapr_tce)
 /* Available with KVM_CAP_RMA */
 #define KVM_ALLOCATE_RMA	  _IOR(KVMIO,  0xa9, struct kvm_allocate_rma)
+/* VM is being stopped by host */
+#define KVM_GUEST_PAUSED	  _IO(KVMIO,   0xaa)
 
 #define KVM_DEV_ASSIGN_ENABLE_IOMMU	(1 << 0)
 
-- 
1.7.5.4

[PATCH 4/5 V4] Add generic stubs for kvm stop check functions

[Eric B Munson]

Signed-off-by: Eric B Munson <emunson@mgebm.net>
Cc: mingo@redhat.com
Cc: hpa@zytor.com
Cc: arnd@arndb.de
Cc: ryanh@linux.vnet.ibm.com
Cc: aliguori@us.ibm.com
Cc: mtosatti@redhat.com
Cc: jeremy.fitzhardinge@citrix.com
Cc: kvm@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
---
 include/asm-generic/kvm_para.h |   14 ++++++++++++++
 1 files changed, 14 insertions(+), 0 deletions(-)
 create mode 100644 include/asm-generic/kvm_para.h

diff --git a/include/asm-generic/kvm_para.h b/include/asm-generic/kvm_para.h
new file mode 100644
index 0000000..177e1eb
--- /dev/null
+++ b/include/asm-generic/kvm_para.h
@@ -0,0 +1,14 @@
+#ifndef _ASM_GENERIC_KVM_PARA_H
+#define _ASM_GENERIC_KVM_PARA_H
+
+
+/*
+ * This function is used by architectures that support kvm to avoid issuing
+ * false soft lockup messages.
+ */
+static inline bool kvm_check_and_clear_guest_paused(int cpu)
+{
+	return false;
+}
+
+#endif
-- 
1.7.5.4

[PATCH 5/5 V4] Add check for suspended vm in softlockup detector

[Eric B Munson]

A suspended VM can cause spurious soft lockup warnings.  To avoid these, the
watchdog now checks if the kernel knows it was stopped by the host and skips
the warning if so.  When the watchdog is reset successfully, clear the guest
paused flag.

Signed-off-by: Eric B Munson <emunson@mgebm.net>
Cc: mingo@redhat.com
Cc: hpa@zytor.com
Cc: arnd@arndb.de
Cc: ryanh@linux.vnet.ibm.com
Cc: aliguori@us.ibm.com
Cc: mtosatti@redhat.com
Cc: jeremy.fitzhardinge@citrix.com
Cc: kvm@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
---
Changes from V3:
 Clear the PAUSED flag when the watchdog is reset

 kernel/watchdog.c |   12 ++++++++++++
 1 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 1d7bca7..7c62919 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -25,6 +25,7 @@
 #include <linux/sysctl.h>
 
 #include <asm/irq_regs.h>
+#include <linux/kvm_para.h>
 #include <linux/perf_event.h>
 
 int watchdog_enabled = 1;
@@ -280,6 +281,9 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 			__this_cpu_write(softlockup_touch_sync, false);
 			sched_clock_tick();
 		}
+
+		/* Clear the guest paused flag on watchdog reset */
+		kvm_check_and_clear_guest_paused(smp_processor_id());
 		__touch_watchdog();
 		return HRTIMER_RESTART;
 	}
@@ -292,6 +296,14 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 	 */
 	duration = is_softlockup(touch_ts);
 	if (unlikely(duration)) {
+		/*
+		 * If a virtual machine is stopped by the host it can look to
+		 * the watchdog like a soft lockup, check to see if the host
+		 * stopped the vm before we issue the warning
+		 */
+		if (kvm_check_and_clear_guest_paused(smp_processor_id()))
+			return HRTIMER_RESTART;
+
 		/* only warn once */
 		if (__this_cpu_read(soft_watchdog_warn) == true)
 			return HRTIMER_RESTART;
-- 
1.7.5.4

Re: [PATCH 0/5 V4] Avoid soft lockup message when KVM is stopped by host

[Marcelo Tosatti]

On Tue, Nov 29, 2011 at 04:35:34PM -0500, Eric B Munson wrote:
> Changes from V3:
> Include CC's on patch 3
> Drop clear flag ioctl and have the watchdog clear the flag when it is reset
> 
> Changes from V2:
> A new kvm functions defined in kvm_para.h, the only change to pvclock is the
> initial flag definition
> 
> Changes from V1:
> (Thanks Marcelo)
> Host code has all been moved to arch/x86/kvm/x86.c
> KVM_PAUSE_GUEST was renamed to KVM_GUEST_PAUSED
> 
> When a guest kernel is stopped by the host hypervisor it can look like a soft
> lockup to the guest kernel.  This false warning can mask later soft lockup
> warnings which may be real.  This patch series adds a method for a host
> hypervisor to communicate to a guest kernel that it is being stopped.  The
> final patch in the series has the watchdog check this flag when it goes to
> issue a soft lockup warning and skip the warning if the guest knows it was
> stopped.
> 
> It was attempted to solve this in Qemu, but the side effects of saving and
> restoring the clock and tsc for each vcpu put the wall clock of the guest behind
> by the amount of time of the pause.  This forces a guest to have ntp running
> in order to keep the wall clock accurate.

Looks good to me.

Re: [PATCH 3/5 V4] Add ioctl for KVM_GUEST_STOPPED

[Sasha Levin]

On Tue, 2011-11-29 at 16:35 -0500, Eric B Munson wrote:
> 
> Now that we have a flag that will tell the guest it was suspended,
> create an interface for that communication using a KVM ioctl.
> 
> Signed-off-by: Eric B Munson <emunson@mgebm.net> 

Can it be documented in api.txt as well?

-- 

Sasha.

Re: [PATCH 3/5 V4] Add ioctl for KVM_GUEST_STOPPED

[Eric B Munson]

[-- Attachment #1: Type: text/plain, Size: 435 bytes --]

On Sat, 03 Dec 2011, Sasha Levin wrote:

> On Tue, 2011-11-29 at 16:35 -0500, Eric B Munson wrote:
> > 
> > Now that we have a flag that will tell the guest it was suspended,
> > create an interface for that communication using a KVM ioctl.
> > 
> > Signed-off-by: Eric B Munson <emunson@mgebm.net> 
> 
> Can it be documented in api.txt as well?
> 
> -- 
> 
> Sasha.
> 

Thanks for the review, will do for V5.

Eric

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