[PATCH 0/4 V16] Avoid soft lockup message when KVM is stopped by host

[PATCH 0/4 V16] Avoid soft lockup message when KVM is stopped by host

[Eric B Munson]

Changes from V15:
Add arch/*/include/asm/kvm_para.h that includes the asm-generic version

Changes from V14:
Update documentation for the pvclock api

Changes from V13:
Expand on KVM_KVMCLOCK_CTRL ioctl documentation

Changes from V12:
Re-add missing kvm.c code after rebase
Rename CAP to KVM_CAP_KVMCLOCK_CTRL
Rename ioctl to KVM_KVMCLOCK_CTRL

Changes from V11:
Re-add asm-generic stub
Correct api.txt typo
add kvm_make_request() call after setting PVCLOCK_GUEST_STOPPED

Changes from V10:
Return ioctl to per vcpu instead of per vm

Changes from V9:
Use kvm_for_each_vcpu to iterate online vcpu's

Changes from V8:
Make KVM_GUEST_PAUSED a per vm ioctl instead of per vcpu

Changes from V7:
Define KVM_CAP_GUEST_PAUSED and support check
Call mark_page_dirty () after setting PVCLOCK_GUEST_STOPPED

Changes from V6:
Use __this_cpu_and when clearing the PVCLOCK_GUEST_STOPPED flag

Changes from V5:
Collapse generic check_and_clear_guest_stopped into patch 2
Include check_and_clear_guest_stopped defintion to ia64, s390, and powerpc
Change check_and_clear_guest_stopped to use __get_cpu_var instead of taking the
 cpuid arg.
Protect check_and_clear_guest_stopped declaration with CONFIG_KVM_CLOCK check

Changes from V4:
Rename KVM_GUEST_PAUSED to KVMCLOCK_GUEST_PAUSED
Add description of KVMCLOCK_GUEST_PAUSED ioctl to api.txt

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: ryanh@linux.vnet.ibm.com
Cc: aliguori@us.ibm.com
Cc: mtosatti@redhat.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 (4):
  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_KVMCLOCK_CTRL
  Add check for suspended vm in softlockup detector

 Documentation/virtual/kvm/api.txt      |   20 ++++++++++++++++++++
 Documentation/virtual/kvm/msr.txt      |    4 ++++
 arch/alpha/include/asm/kvm_para.h      |    1 +
 arch/arm/include/asm/kvm_para.h        |    1 +
 arch/avr32/include/asm/kvm_para.h      |    1 +
 arch/blackfin/include/asm/kvm_para.h   |    1 +
 arch/c6x/include/asm/kvm_para.h        |    1 +
 arch/frv/include/asm/kvm_para.h        |    1 +
 arch/h8300/include/asm/kvm_para.h      |    1 +
 arch/hexagon/include/asm/kvm_para.h    |    1 +
 arch/ia64/include/asm/kvm_para.h       |    5 +++++
 arch/m68k/include/asm/kvm_para.h       |    1 +
 arch/microblaze/include/asm/kvm_para.h |    1 +
 arch/mips/include/asm/kvm_para.h       |    1 +
 arch/mn10300/include/asm/kvm_para.h    |    1 +
 arch/openrisc/include/asm/kvm_para.h   |    1 +
 arch/parisc/include/asm/kvm_para.h     |    1 +
 arch/powerpc/include/asm/kvm_para.h    |    5 +++++
 arch/s390/include/asm/kvm_para.h       |    5 +++++
 arch/score/include/asm/kvm_para.h      |    1 +
 arch/sh/include/asm/kvm_para.h         |    1 +
 arch/sparc/include/asm/kvm_para.h      |    1 +
 arch/tile/include/asm/kvm_para.h       |    1 +
 arch/um/include/asm/kvm_para.h         |    1 +
 arch/unicore32/include/asm/kvm_para.h  |    1 +
 arch/x86/include/asm/kvm_para.h        |    8 ++++++++
 arch/x86/include/asm/pvclock-abi.h     |    1 +
 arch/x86/kernel/kvmclock.c             |   21 +++++++++++++++++++++
 arch/x86/kvm/x86.c                     |   22 ++++++++++++++++++++++
 arch/xtensa/include/asm/kvm_para.h     |    1 +
 include/asm-generic/kvm_para.h         |   14 ++++++++++++++
 include/linux/kvm.h                    |    3 +++
 kernel/watchdog.c                      |   12 ++++++++++++
 33 files changed, 141 insertions(+), 0 deletions(-)
 create mode 100644 arch/alpha/include/asm/kvm_para.h
 create mode 100644 arch/arm/include/asm/kvm_para.h
 create mode 100644 arch/avr32/include/asm/kvm_para.h
 create mode 100644 arch/blackfin/include/asm/kvm_para.h
 create mode 100644 arch/c6x/include/asm/kvm_para.h
 create mode 100644 arch/frv/include/asm/kvm_para.h
 create mode 100644 arch/h8300/include/asm/kvm_para.h
 create mode 100644 arch/hexagon/include/asm/kvm_para.h
 create mode 100644 arch/m68k/include/asm/kvm_para.h
 create mode 100644 arch/microblaze/include/asm/kvm_para.h
 create mode 100644 arch/mips/include/asm/kvm_para.h
 create mode 100644 arch/mn10300/include/asm/kvm_para.h
 create mode 100644 arch/openrisc/include/asm/kvm_para.h
 create mode 100644 arch/parisc/include/asm/kvm_para.h
 create mode 100644 arch/score/include/asm/kvm_para.h
 create mode 100644 arch/sh/include/asm/kvm_para.h
 create mode 100644 arch/sparc/include/asm/kvm_para.h
 create mode 100644 arch/tile/include/asm/kvm_para.h
 create mode 100644 arch/um/include/asm/kvm_para.h
 create mode 100644 arch/unicore32/include/asm/kvm_para.h
 create mode 100644 arch/xtensa/include/asm/kvm_para.h
 create mode 100644 include/asm-generic/kvm_para.h

-- 
1.7.5.4

[PATCH 1/4 V16] 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: ryanh@linux.vnet.ibm.com
Cc: aliguori@us.ibm.com
Cc: mtosatti@redhat.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 2/4 V16] 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>
asm-generic changes Acked-by: Arnd Bergmann <arnd@arndb.de>
Cc: mingo@redhat.com
Cc: hpa@zytor.com
Cc: ryanh@linux.vnet.ibm.com
Cc: aliguori@us.ibm.com
Cc: mtosatti@redhat.com
Cc: kvm@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
---
Changes from V15:
 Add stubs to include asm-generic/kvm_para.h where necessary
Changes from V11:
 Re-add the missing asm-generic stub for check_and_clear_guest_stopped()
Changes from V6:
 Use __this_cpu_and when clearing the PVCLOCK_GUEST_STOPPED flag
Changes from V5:
 Collapse generic stubs into this patch
 check_and_clear_guest_stopped() takes no args and uses __get_cpu_var()
 Include individual definitions in ia64, s390, and powerpc

 arch/alpha/include/asm/kvm_para.h      |    1 +
 arch/arm/include/asm/kvm_para.h        |    1 +
 arch/avr32/include/asm/kvm_para.h      |    1 +
 arch/blackfin/include/asm/kvm_para.h   |    1 +
 arch/c6x/include/asm/kvm_para.h        |    1 +
 arch/frv/include/asm/kvm_para.h        |    1 +
 arch/h8300/include/asm/kvm_para.h      |    1 +
 arch/hexagon/include/asm/kvm_para.h    |    1 +
 arch/ia64/include/asm/kvm_para.h       |    5 +++++
 arch/m68k/include/asm/kvm_para.h       |    1 +
 arch/microblaze/include/asm/kvm_para.h |    1 +
 arch/mips/include/asm/kvm_para.h       |    1 +
 arch/mn10300/include/asm/kvm_para.h    |    1 +
 arch/openrisc/include/asm/kvm_para.h   |    1 +
 arch/parisc/include/asm/kvm_para.h     |    1 +
 arch/powerpc/include/asm/kvm_para.h    |    5 +++++
 arch/s390/include/asm/kvm_para.h       |    5 +++++
 arch/score/include/asm/kvm_para.h      |    1 +
 arch/sh/include/asm/kvm_para.h         |    1 +
 arch/sparc/include/asm/kvm_para.h      |    1 +
 arch/tile/include/asm/kvm_para.h       |    1 +
 arch/um/include/asm/kvm_para.h         |    1 +
 arch/unicore32/include/asm/kvm_para.h  |    1 +
 arch/x86/include/asm/kvm_para.h        |    8 ++++++++
 arch/x86/kernel/kvmclock.c             |   21 +++++++++++++++++++++
 arch/xtensa/include/asm/kvm_para.h     |    1 +
 include/asm-generic/kvm_para.h         |   14 ++++++++++++++
 27 files changed, 79 insertions(+), 0 deletions(-)
 create mode 100644 arch/alpha/include/asm/kvm_para.h
 create mode 100644 arch/arm/include/asm/kvm_para.h
 create mode 100644 arch/avr32/include/asm/kvm_para.h
 create mode 100644 arch/blackfin/include/asm/kvm_para.h
 create mode 100644 arch/c6x/include/asm/kvm_para.h
 create mode 100644 arch/frv/include/asm/kvm_para.h
 create mode 100644 arch/h8300/include/asm/kvm_para.h
 create mode 100644 arch/hexagon/include/asm/kvm_para.h
 create mode 100644 arch/m68k/include/asm/kvm_para.h
 create mode 100644 arch/microblaze/include/asm/kvm_para.h
 create mode 100644 arch/mips/include/asm/kvm_para.h
 create mode 100644 arch/mn10300/include/asm/kvm_para.h
 create mode 100644 arch/openrisc/include/asm/kvm_para.h
 create mode 100644 arch/parisc/include/asm/kvm_para.h
 create mode 100644 arch/score/include/asm/kvm_para.h
 create mode 100644 arch/sh/include/asm/kvm_para.h
 create mode 100644 arch/sparc/include/asm/kvm_para.h
 create mode 100644 arch/tile/include/asm/kvm_para.h
 create mode 100644 arch/um/include/asm/kvm_para.h
 create mode 100644 arch/unicore32/include/asm/kvm_para.h
 create mode 100644 arch/xtensa/include/asm/kvm_para.h
 create mode 100644 include/asm-generic/kvm_para.h

diff --git a/arch/alpha/include/asm/kvm_para.h b/arch/alpha/include/asm/kvm_para.h
new file mode 100644
index 0000000..14fab8f
--- /dev/null
+++ b/arch/alpha/include/asm/kvm_para.h
@@ -0,0 +1 @@
+#include <asm-generic/kvm_para.h>
diff --git a/arch/arm/include/asm/kvm_para.h b/arch/arm/include/asm/kvm_para.h
new file mode 100644
index 0000000..14fab8f
--- /dev/null
+++ b/arch/arm/include/asm/kvm_para.h
@@ -0,0 +1 @@
+#include <asm-generic/kvm_para.h>
diff --git a/arch/avr32/include/asm/kvm_para.h b/arch/avr32/include/asm/kvm_para.h
new file mode 100644
index 0000000..14fab8f
--- /dev/null
+++ b/arch/avr32/include/asm/kvm_para.h
@@ -0,0 +1 @@
+#include <asm-generic/kvm_para.h>
diff --git a/arch/blackfin/include/asm/kvm_para.h b/arch/blackfin/include/asm/kvm_para.h
new file mode 100644
index 0000000..14fab8f
--- /dev/null
+++ b/arch/blackfin/include/asm/kvm_para.h
@@ -0,0 +1 @@
+#include <asm-generic/kvm_para.h>
diff --git a/arch/c6x/include/asm/kvm_para.h b/arch/c6x/include/asm/kvm_para.h
new file mode 100644
index 0000000..14fab8f
--- /dev/null
+++ b/arch/c6x/include/asm/kvm_para.h
@@ -0,0 +1 @@
+#include <asm-generic/kvm_para.h>
diff --git a/arch/frv/include/asm/kvm_para.h b/arch/frv/include/asm/kvm_para.h
new file mode 100644
index 0000000..14fab8f
--- /dev/null
+++ b/arch/frv/include/asm/kvm_para.h
@@ -0,0 +1 @@
+#include <asm-generic/kvm_para.h>
diff --git a/arch/h8300/include/asm/kvm_para.h b/arch/h8300/include/asm/kvm_para.h
new file mode 100644
index 0000000..14fab8f
--- /dev/null
+++ b/arch/h8300/include/asm/kvm_para.h
@@ -0,0 +1 @@
+#include <asm-generic/kvm_para.h>
diff --git a/arch/hexagon/include/asm/kvm_para.h b/arch/hexagon/include/asm/kvm_para.h
new file mode 100644
index 0000000..14fab8f
--- /dev/null
+++ b/arch/hexagon/include/asm/kvm_para.h
@@ -0,0 +1 @@
+#include <asm-generic/kvm_para.h>
diff --git a/arch/ia64/include/asm/kvm_para.h b/arch/ia64/include/asm/kvm_para.h
index 1588aee..2019cb9 100644
--- a/arch/ia64/include/asm/kvm_para.h
+++ b/arch/ia64/include/asm/kvm_para.h
@@ -26,6 +26,11 @@ static inline unsigned int kvm_arch_para_features(void)
 	return 0;
 }
 
+static inline bool kvm_check_and_clear_guest_paused(void)
+{
+	return false;
+}
+
 #endif
 
 #endif
diff --git a/arch/m68k/include/asm/kvm_para.h b/arch/m68k/include/asm/kvm_para.h
new file mode 100644
index 0000000..14fab8f
--- /dev/null
+++ b/arch/m68k/include/asm/kvm_para.h
@@ -0,0 +1 @@
+#include <asm-generic/kvm_para.h>
diff --git a/arch/microblaze/include/asm/kvm_para.h b/arch/microblaze/include/asm/kvm_para.h
new file mode 100644
index 0000000..14fab8f
--- /dev/null
+++ b/arch/microblaze/include/asm/kvm_para.h
@@ -0,0 +1 @@
+#include <asm-generic/kvm_para.h>
diff --git a/arch/mips/include/asm/kvm_para.h b/arch/mips/include/asm/kvm_para.h
new file mode 100644
index 0000000..14fab8f
--- /dev/null
+++ b/arch/mips/include/asm/kvm_para.h
@@ -0,0 +1 @@
+#include <asm-generic/kvm_para.h>
diff --git a/arch/mn10300/include/asm/kvm_para.h b/arch/mn10300/include/asm/kvm_para.h
new file mode 100644
index 0000000..14fab8f
--- /dev/null
+++ b/arch/mn10300/include/asm/kvm_para.h
@@ -0,0 +1 @@
+#include <asm-generic/kvm_para.h>
diff --git a/arch/openrisc/include/asm/kvm_para.h b/arch/openrisc/include/asm/kvm_para.h
new file mode 100644
index 0000000..14fab8f
--- /dev/null
+++ b/arch/openrisc/include/asm/kvm_para.h
@@ -0,0 +1 @@
+#include <asm-generic/kvm_para.h>
diff --git a/arch/parisc/include/asm/kvm_para.h b/arch/parisc/include/asm/kvm_para.h
new file mode 100644
index 0000000..14fab8f
--- /dev/null
+++ b/arch/parisc/include/asm/kvm_para.h
@@ -0,0 +1 @@
+#include <asm-generic/kvm_para.h>
diff --git a/arch/powerpc/include/asm/kvm_para.h b/arch/powerpc/include/asm/kvm_para.h
index 7b754e7..c18916b 100644
--- a/arch/powerpc/include/asm/kvm_para.h
+++ b/arch/powerpc/include/asm/kvm_para.h
@@ -206,6 +206,11 @@ static inline unsigned int kvm_arch_para_features(void)
 	return r;
 }
 
+static inline bool kvm_check_and_clear_guest_paused(void)
+{
+	return false;
+}
+
 #endif /* __KERNEL__ */
 
 #endif /* __POWERPC_KVM_PARA_H__ */
diff --git a/arch/s390/include/asm/kvm_para.h b/arch/s390/include/asm/kvm_para.h
index 6964db2..a988329 100644
--- a/arch/s390/include/asm/kvm_para.h
+++ b/arch/s390/include/asm/kvm_para.h
@@ -149,6 +149,11 @@ static inline unsigned int kvm_arch_para_features(void)
 	return 0;
 }
 
+static inline bool kvm_check_and_clear_guest_paused(void)
+{
+	return false;
+}
+
 #endif
 
 #endif /* __S390_KVM_PARA_H */
diff --git a/arch/score/include/asm/kvm_para.h b/arch/score/include/asm/kvm_para.h
new file mode 100644
index 0000000..14fab8f
--- /dev/null
+++ b/arch/score/include/asm/kvm_para.h
@@ -0,0 +1 @@
+#include <asm-generic/kvm_para.h>
diff --git a/arch/sh/include/asm/kvm_para.h b/arch/sh/include/asm/kvm_para.h
new file mode 100644
index 0000000..14fab8f
--- /dev/null
+++ b/arch/sh/include/asm/kvm_para.h
@@ -0,0 +1 @@
+#include <asm-generic/kvm_para.h>
diff --git a/arch/sparc/include/asm/kvm_para.h b/arch/sparc/include/asm/kvm_para.h
new file mode 100644
index 0000000..14fab8f
--- /dev/null
+++ b/arch/sparc/include/asm/kvm_para.h
@@ -0,0 +1 @@
+#include <asm-generic/kvm_para.h>
diff --git a/arch/tile/include/asm/kvm_para.h b/arch/tile/include/asm/kvm_para.h
new file mode 100644
index 0000000..14fab8f
--- /dev/null
+++ b/arch/tile/include/asm/kvm_para.h
@@ -0,0 +1 @@
+#include <asm-generic/kvm_para.h>
diff --git a/arch/um/include/asm/kvm_para.h b/arch/um/include/asm/kvm_para.h
new file mode 100644
index 0000000..14fab8f
--- /dev/null
+++ b/arch/um/include/asm/kvm_para.h
@@ -0,0 +1 @@
+#include <asm-generic/kvm_para.h>
diff --git a/arch/unicore32/include/asm/kvm_para.h b/arch/unicore32/include/asm/kvm_para.h
new file mode 100644
index 0000000..14fab8f
--- /dev/null
+++ b/arch/unicore32/include/asm/kvm_para.h
@@ -0,0 +1 @@
+#include <asm-generic/kvm_para.h>
diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
index 734c376..99c4bbe 100644
--- a/arch/x86/include/asm/kvm_para.h
+++ b/arch/x86/include/asm/kvm_para.h
@@ -95,6 +95,14 @@ struct kvm_vcpu_pv_apf_data {
 extern void kvmclock_init(void);
 extern int kvm_register_clock(char *txt);
 
+#ifdef CONFIG_KVM_CLOCK
+bool kvm_check_and_clear_guest_paused(void);
+#else
+static inline bool kvm_check_and_clear_guest_paused(void)
+{
+	return false;
+}
+#endif /* CONFIG_KVMCLOCK */
 
 /* 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 f8492da..4ba090c 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(void)
+{
+	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 = &__get_cpu_var(hv_clock);
+	if ((src->flags & PVCLOCK_GUEST_STOPPED) != 0) {
+		__this_cpu_and(hv_clock.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,
diff --git a/arch/xtensa/include/asm/kvm_para.h b/arch/xtensa/include/asm/kvm_para.h
new file mode 100644
index 0000000..14fab8f
--- /dev/null
+++ b/arch/xtensa/include/asm/kvm_para.h
@@ -0,0 +1 @@
+#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..05ef7e7
--- /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(void)
+{
+	return false;
+}
+
+#endif
-- 
1.7.5.4

[PATCH 3/4 V16] Add ioctl for KVM_KVMCLOCK_CTRL

[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: ryanh@linux.vnet.ibm.com
Cc: aliguori@us.ibm.com
Cc: mtosatti@redhat.com
Cc: kvm@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
---
Changes from V14:
 Add description of flags bit used for host->guest communication
Changes from V13:
 Expand the ioctl documentation
Changes from V12:
 Rename KVM_CAP and KVM ioctl
Changes from V11:
 Correct typo in api.txt
 Add kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu) call to kvm_set_guest_paused()
Changes from V10:
 Return the ioctl to per vcpu instead of per vm
Changes from V9:
 Use kvm_for_each_vcpu to iterate online vcpu's
Changes from V8:
 Make KVM_GUEST_PAUSED a per vm ioctl instead of per vcpu
Changes from V7:
 Define KVM_CAP_GUEST_PAUSED and support check
 Call mark_page_dirty () after setting PVCLOCK_GUEST_STOPPED
Changes from V4:
 Rename KVM_GUEST_PAUSED to KVMCLOCK_GUEST_PAUSED
 Add new ioctl description to api.txt

 Documentation/virtual/kvm/api.txt |   20 ++++++++++++++++++++
 Documentation/virtual/kvm/msr.txt |    4 ++++
 arch/x86/kvm/x86.c                |   22 ++++++++++++++++++++++
 include/linux/kvm.h               |    3 +++
 4 files changed, 49 insertions(+), 0 deletions(-)

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 6386f8c..81ff39f 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1669,6 +1669,26 @@ at the memory location pointed to by "addr".
 The list of registers accessible using this interface is identical to the
 list in 4.64.
 
+4.70 KVM_KVMCLOCK_CTRL
+
+Capability: KVM_CAP_KVMCLOCK_CTRL
+Architectures: Any that implement pvclocks (currently x86 only)
+Type: vcpu ioctl
+Parameters: None
+Returns: 0 on success, -1 on error
+
+This signals to the host kernel that the specified guest is being paused by
+userspace.  The host will set a flag in the pvclock structure that is checked
+from the soft lockup watchdog.  The flag is part of the pvclock structure that
+is shared between guest and host, specifically the second bit of the flags
+field of the pvclock_vcpu_time_info structure.  It will be set exclusively by
+the host and read/cleared exclusively by the guest.  The guest operation of
+checking and clearing the flag must an atomic operation so
+load-link/store-conditional, or equivalent must be used.  There are two cases
+where the guest will clear the flag: when the soft lockup watchdog timer resets
+itself or when a soft lockup is detected.  This ioctl can be called any time
+after pausing the vcpu, but before it is resumed.
+
 5. The kvm_run structure
 
 Application code obtains a pointer to the kvm_run structure by
diff --git a/Documentation/virtual/kvm/msr.txt b/Documentation/virtual/kvm/msr.txt
index 5031780..96b41bd 100644
--- a/Documentation/virtual/kvm/msr.txt
+++ b/Documentation/virtual/kvm/msr.txt
@@ -109,6 +109,10 @@ MSR_KVM_SYSTEM_TIME_NEW:  0x4b564d01
 		     0      |	   24      | multiple cpus are guaranteed to
 			    |		   | be monotonic
 		-------------------------------------------------------------
+			    |		   | guest vcpu has been paused by
+		     1	    |	  N/A	   | the host
+			    |		   | See 4.70 in api.txt
+		-------------------------------------------------------------
 
 	Availability of this MSR must be checked via bit 3 in 0x4000001 cpuid
 	leaf prior to usage.
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7ce5878..4e1bf3b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2145,6 +2145,7 @@ int kvm_dev_ioctl_check_extension(long ext)
 	case KVM_CAP_ASYNC_PF:
 	case KVM_CAP_GET_TSC_KHZ:
 	case KVM_CAP_PCI_2_3:
+	case KVM_CAP_KVMCLOCK_CTRL:
 		r = 1;
 		break;
 	case KVM_CAP_COALESCED_MMIO:
@@ -2595,6 +2596,23 @@ static int kvm_vcpu_ioctl_x86_set_xcrs(struct kvm_vcpu *vcpu,
 	return r;
 }
 
+/*
+ * 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.
+ */
+static 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;
+	mark_page_dirty(vcpu->kvm, vcpu->arch.time >> PAGE_SHIFT);
+	kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
+	return 0;
+}
+
 long kvm_arch_vcpu_ioctl(struct file *filp,
 			 unsigned int ioctl, unsigned long arg)
 {
@@ -2871,6 +2889,10 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 		r = vcpu->arch.virtual_tsc_khz;
 		goto out;
 	}
+	case KVM_KVMCLOCK_CTRL: {
+		r = kvm_set_guest_paused(vcpu);
+		goto out;
+	}
 	default:
 		r = -EINVAL;
 	}
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 6c322a9..7a9dd4b 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -589,6 +589,7 @@ struct kvm_ppc_pvinfo {
 #define KVM_CAP_S390_UCONTROL 73
 #define KVM_CAP_SYNC_REGS 74
 #define KVM_CAP_PCI_2_3 75
+#define KVM_CAP_KVMCLOCK_CTRL 76
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -859,6 +860,8 @@ struct kvm_s390_ucas_mapping {
 /* Available with KVM_CAP_ONE_REG */
 #define KVM_GET_ONE_REG		  _IOW(KVMIO,  0xab, struct kvm_one_reg)
 #define KVM_SET_ONE_REG		  _IOW(KVMIO,  0xac, struct kvm_one_reg)
+/* VM is being stopped by host */
+#define KVM_KVMCLOCK_CTRL	  _IO(KVMIO,   0xad)
 
 #define KVM_DEV_ASSIGN_ENABLE_IOMMU	(1 << 0)
 #define KVM_DEV_ASSIGN_PCI_2_3		(1 << 1)
-- 
1.7.5.4

[PATCH 4/4 V16] 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: ryanh@linux.vnet.ibm.com
Cc: aliguori@us.ibm.com
Cc: mtosatti@redhat.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 d117262..f6ffdc2 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();
 		__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())
+			return HRTIMER_RESTART;
+
 		/* only warn once */
 		if (__this_cpu_read(soft_watchdog_warn) == true)
 			return HRTIMER_RESTART;
-- 
1.7.5.4

Re: [PATCH 0/4 V16] Avoid soft lockup message when KVM is stopped by host

[Marcelo Tosatti]

Applied, thanks.

On Sat, Mar 10, 2012 at 02:37:24PM -0500, Eric B Munson wrote:
> Changes from V15:
> Add arch/*/include/asm/kvm_para.h that includes the asm-generic version
> 
> Changes from V14:
> Update documentation for the pvclock api
> 
> Changes from V13:
> Expand on KVM_KVMCLOCK_CTRL ioctl documentation
> 
> Changes from V12:
> Re-add missing kvm.c code after rebase
> Rename CAP to KVM_CAP_KVMCLOCK_CTRL
> Rename ioctl to KVM_KVMCLOCK_CTRL
> 
> Changes from V11:
> Re-add asm-generic stub
> Correct api.txt typo
> add kvm_make_request() call after setting PVCLOCK_GUEST_STOPPED
> 
> Changes from V10:
> Return ioctl to per vcpu instead of per vm
> 
> Changes from V9:
> Use kvm_for_each_vcpu to iterate online vcpu's
> 
> Changes from V8:
> Make KVM_GUEST_PAUSED a per vm ioctl instead of per vcpu
> 
> Changes from V7:
> Define KVM_CAP_GUEST_PAUSED and support check
> Call mark_page_dirty () after setting PVCLOCK_GUEST_STOPPED
> 
> Changes from V6:
> Use __this_cpu_and when clearing the PVCLOCK_GUEST_STOPPED flag
> 
> Changes from V5:
> Collapse generic check_and_clear_guest_stopped into patch 2
> Include check_and_clear_guest_stopped defintion to ia64, s390, and powerpc
> Change check_and_clear_guest_stopped to use __get_cpu_var instead of taking the
>  cpuid arg.
> Protect check_and_clear_guest_stopped declaration with CONFIG_KVM_CLOCK check
> 
> Changes from V4:
> Rename KVM_GUEST_PAUSED to KVMCLOCK_GUEST_PAUSED
> Add description of KVMCLOCK_GUEST_PAUSED ioctl to api.txt
> 
> 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: ryanh@linux.vnet.ibm.com
> Cc: aliguori@us.ibm.com
> Cc: mtosatti@redhat.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 (4):
>   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_KVMCLOCK_CTRL
>   Add check for suspended vm in softlockup detector
> 
>  Documentation/virtual/kvm/api.txt      |   20 ++++++++++++++++++++
>  Documentation/virtual/kvm/msr.txt      |    4 ++++
>  arch/alpha/include/asm/kvm_para.h      |    1 +
>  arch/arm/include/asm/kvm_para.h        |    1 +
>  arch/avr32/include/asm/kvm_para.h      |    1 +
>  arch/blackfin/include/asm/kvm_para.h   |    1 +
>  arch/c6x/include/asm/kvm_para.h        |    1 +
>  arch/frv/include/asm/kvm_para.h        |    1 +
>  arch/h8300/include/asm/kvm_para.h      |    1 +
>  arch/hexagon/include/asm/kvm_para.h    |    1 +
>  arch/ia64/include/asm/kvm_para.h       |    5 +++++
>  arch/m68k/include/asm/kvm_para.h       |    1 +
>  arch/microblaze/include/asm/kvm_para.h |    1 +
>  arch/mips/include/asm/kvm_para.h       |    1 +
>  arch/mn10300/include/asm/kvm_para.h    |    1 +
>  arch/openrisc/include/asm/kvm_para.h   |    1 +
>  arch/parisc/include/asm/kvm_para.h     |    1 +
>  arch/powerpc/include/asm/kvm_para.h    |    5 +++++
>  arch/s390/include/asm/kvm_para.h       |    5 +++++
>  arch/score/include/asm/kvm_para.h      |    1 +
>  arch/sh/include/asm/kvm_para.h         |    1 +
>  arch/sparc/include/asm/kvm_para.h      |    1 +
>  arch/tile/include/asm/kvm_para.h       |    1 +
>  arch/um/include/asm/kvm_para.h         |    1 +
>  arch/unicore32/include/asm/kvm_para.h  |    1 +
>  arch/x86/include/asm/kvm_para.h        |    8 ++++++++
>  arch/x86/include/asm/pvclock-abi.h     |    1 +
>  arch/x86/kernel/kvmclock.c             |   21 +++++++++++++++++++++
>  arch/x86/kvm/x86.c                     |   22 ++++++++++++++++++++++
>  arch/xtensa/include/asm/kvm_para.h     |    1 +
>  include/asm-generic/kvm_para.h         |   14 ++++++++++++++
>  include/linux/kvm.h                    |    3 +++
>  kernel/watchdog.c                      |   12 ++++++++++++
>  33 files changed, 141 insertions(+), 0 deletions(-)
>  create mode 100644 arch/alpha/include/asm/kvm_para.h
>  create mode 100644 arch/arm/include/asm/kvm_para.h
>  create mode 100644 arch/avr32/include/asm/kvm_para.h
>  create mode 100644 arch/blackfin/include/asm/kvm_para.h
>  create mode 100644 arch/c6x/include/asm/kvm_para.h
>  create mode 100644 arch/frv/include/asm/kvm_para.h
>  create mode 100644 arch/h8300/include/asm/kvm_para.h
>  create mode 100644 arch/hexagon/include/asm/kvm_para.h
>  create mode 100644 arch/m68k/include/asm/kvm_para.h
>  create mode 100644 arch/microblaze/include/asm/kvm_para.h
>  create mode 100644 arch/mips/include/asm/kvm_para.h
>  create mode 100644 arch/mn10300/include/asm/kvm_para.h
>  create mode 100644 arch/openrisc/include/asm/kvm_para.h
>  create mode 100644 arch/parisc/include/asm/kvm_para.h
>  create mode 100644 arch/score/include/asm/kvm_para.h
>  create mode 100644 arch/sh/include/asm/kvm_para.h
>  create mode 100644 arch/sparc/include/asm/kvm_para.h
>  create mode 100644 arch/tile/include/asm/kvm_para.h
>  create mode 100644 arch/um/include/asm/kvm_para.h
>  create mode 100644 arch/unicore32/include/asm/kvm_para.h
>  create mode 100644 arch/xtensa/include/asm/kvm_para.h
>  create mode 100644 include/asm-generic/kvm_para.h
> 
> -- 
> 1.7.5.4
> 
> --
> To unsubscribe from this list: send the line "unsubscribe kvm" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH 2/4 V16] Add functions to check if the host has stopped the vm

[Jan Kiszka]

On 2012-03-10 20:37, Eric B Munson wrote:
> 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.
> 

...

> diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> index f8492da..4ba090c 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(void)
> +{
> +	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 = &__get_cpu_var(hv_clock);
> +	if ((src->flags & PVCLOCK_GUEST_STOPPED) != 0) {
> +		__this_cpu_and(hv_clock.flags, ~PVCLOCK_GUEST_STOPPED);
> +		ret = true;
> +	}
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(kvm_check_and_clear_guest_paused);

Which module is going to use this? I failed to find it, but I may have
missed something.

The actual reason for this reply: this patches causes a compiler warning
here, likely due to lacking include for EXPORT_SYMBOL_GPL:

  CC      arch/x86/kernel/kvmclock.o
/data/linux-kvm/arch/x86/kernel/kvmclock.c:136:1: warning: data
definition has no type or storage class
/data/linux-kvm/arch/x86/kernel/kvmclock.c:136:1: warning: type defaults
to ‘int’ in declaration of ‘EXPORT_SYMBOL_GPL’
/data/linux-kvm/arch/x86/kernel/kvmclock.c:136:1: warning: parameter
names (without types) in function declaration

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux

Re: [PATCH 2/4 V16] Add functions to check if the host has stopped the vm

[Eric B Munson]

On Wed, 14 Mar 2012 11:12:35 +0100, Jan Kiszka wrote:
> On 2012-03-10 20:37, Eric B Munson wrote:
>> 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.
>>
>
> ...
>
>> diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
>> index f8492da..4ba090c 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(void)
>> +{
>> +	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 = &__get_cpu_var(hv_clock);
>> +	if ((src->flags & PVCLOCK_GUEST_STOPPED) != 0) {
>> +		__this_cpu_and(hv_clock.flags, ~PVCLOCK_GUEST_STOPPED);
>> +		ret = true;
>> +	}
>> +
>> +	return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(kvm_check_and_clear_guest_paused);
>
> Which module is going to use this? I failed to find it, but I may 
> have
> missed something.
>
> The actual reason for this reply: this patches causes a compiler 
> warning
> here, likely due to lacking include for EXPORT_SYMBOL_GPL:
>
>   CC      arch/x86/kernel/kvmclock.o
> /data/linux-kvm/arch/x86/kernel/kvmclock.c:136:1: warning: data
> definition has no type or storage class
> /data/linux-kvm/arch/x86/kernel/kvmclock.c:136:1: warning: type 
> defaults
> to ‘int’ in declaration of ‘EXPORT_SYMBOL_GPL’
> /data/linux-kvm/arch/x86/kernel/kvmclock.c:136:1: warning: parameter
> names (without types) in function declaration
>
> Jan


I will have a look at these this evening.

Eric

Re: [PATCH 2/4 V16] Add functions to check if the host has stopped the vm

[Eric B Munson]

On Wed, 14 Mar 2012 11:12:35 +0100, Jan Kiszka wrote:
> On 2012-03-10 20:37, Eric B Munson wrote:
>> 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.
>>
>
> ...
>
>> diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
>> index f8492da..4ba090c 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(void)
>> +{
>> +	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 = &__get_cpu_var(hv_clock);
>> +	if ((src->flags & PVCLOCK_GUEST_STOPPED) != 0) {
>> +		__this_cpu_and(hv_clock.flags, ~PVCLOCK_GUEST_STOPPED);
>> +		ret = true;
>> +	}
>> +
>> +	return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(kvm_check_and_clear_guest_paused);
>
> Which module is going to use this? I failed to find it, but I may 
> have
> missed something.
>
> The actual reason for this reply: this patches causes a compiler 
> warning
> here, likely due to lacking include for EXPORT_SYMBOL_GPL:
>
>   CC      arch/x86/kernel/kvmclock.o
> /data/linux-kvm/arch/x86/kernel/kvmclock.c:136:1: warning: data
> definition has no type or storage class
> /data/linux-kvm/arch/x86/kernel/kvmclock.c:136:1: warning: type 
> defaults
> to ‘int’ in declaration of ‘EXPORT_SYMBOL_GPL’
> /data/linux-kvm/arch/x86/kernel/kvmclock.c:136:1: warning: parameter
> names (without types) in function declaration
>
> Jan


There isn't a module that will use it, I was under the (mistaken) 
understanding that
the EXPORT was necessary for use in kernel/watchdog.c.  Give that it 
isn't, I will
post a patch to remove it shortly.

Eric