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Subject[PATCH 6/6] Add age out of guest paused flag
Date
The KVM_GUEST_PAUSED flag will prevent a guest from compaining about a soft
lockup but it can mask real soft lockups if the flag isn't cleared when it is
no longer relevant. This patch adds a kvm ioctl that the hypervisor will use
when it resumes a guest to start a timer for aging out the flag. The time out
will be specified by the hypervisor in the ioctl call.

Signed-off-by: Eric B Munson <emunson@mgebm.net>
---
arch/x86/include/asm/pvclock.h | 2 ++
arch/x86/kernel/kvmclock.c | 24 ++++++++++++++++++++++++
arch/x86/kvm/x86.c | 9 +++++++++
include/linux/kvm.h | 2 ++
include/linux/kvm_host.h | 2 ++
5 files changed, 39 insertions(+), 0 deletions(-)
diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
index 9312814..e8460b9 100644
--- a/arch/x86/include/asm/pvclock.h
+++ b/arch/x86/include/asm/pvclock.h
@@ -18,6 +18,8 @@ void kvm_set_host_stopped(struct kvm_vcpu *vcpu);

bool kvm_check_and_clear_host_stopped(int cpu);

+void kvm_clear_guest_paused(struct kvm_vcpu *vcpu, unsigned int length);
+
/*
* Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
* yielding a 64-bit result.
diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index f4fff3d..f3f3935 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -23,6 +23,8 @@
#include <asm/apic.h>
#include <linux/percpu.h>
#include <linux/kvm_host.h>
+#include <linux/kobject.h>
+#include <linux/sysfs.h>

#include <asm/x86_init.h>
#include <asm/reboot.h>
@@ -144,6 +146,28 @@ bool kvm_check_and_clear_host_stopped(int cpu)
return ret;
}

+static void kvm_timer_clear_guest_paused(unsigned long vcpu_addr)
+{
+ struct kvm_vcpu *vcpu = (struct kvm_vcpu *)vcpu_addr;
+ struct pvclock_vcpu_time_info *src = &vcpu->arch.hv_clock;
+ src->flags = src->flags & (!PVCLOCK_GUEST_STOPPED);
+}
+
+/*
+ * Host has resumed the guest, we need to clear the guest paused flag so we
+ * don't mask any real soft lockups.
+ */
+void kvm_clear_guest_paused(struct kvm_vcpu *vcpu, unsigned int length)
+{
+ if (!timer_pending(&vcpu->flag_timer))
+ setup_timer(&vcpu->flag_timer,
+ kvm_timer_clear_guest_paused,
+ (unsigned long)vcpu);
+ mod_timer(&vcpu->flag_timer,
+ jiffies + (length * HZ));
+}
+EXPORT_SYMBOL_GPL(kvm_clear_guest_paused);
+
static struct clocksource kvm_clock = {
.name = "kvm-clock",
.read = kvm_clock_get_cycles,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 16e029e..b907b5a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3269,6 +3269,15 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
kvm_set_host_stopped(vcpu);
break;
}
+ case KVM_CLEAR_GUEST_PAUSED: {
+ unsigned int length;
+ r = -EFAULT;
+ if (copy_from_user(&length, argp, sizeof length))
+ goto out;
+ r = 0;
+ kvm_clear_guest_paused(vcpu, length);
+ break;
+ }
default:
r = -EINVAL;
}
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index a2697be..f333274 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -761,6 +761,8 @@ struct kvm_clock_data {
#define KVM_ALLOCATE_RMA _IOR(KVMIO, 0xa9, struct kvm_allocate_rma)
/* VM is being stopped by host */
#define KVM_PAUSE_GUEST _IO(KVMIO, 0xaa)
+/* Start the timer to clear the paused flag */
+#define KVM_CLEAR_GUEST_PAUSED _IO(KVMIO, 0xab)

#define KVM_DEV_ASSIGN_ENABLE_IOMMU (1 << 0)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index eabb21a..e21be4b 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -18,6 +18,7 @@
#include <linux/msi.h>
#include <linux/slab.h>
#include <linux/rcupdate.h>
+#include <linux/timer.h>
#include <asm/signal.h>

#include <linux/kvm.h>
@@ -152,6 +153,7 @@ struct kvm_vcpu {
#endif

struct kvm_vcpu_arch arch;
+ struct timer_list flag_timer;
};

static inline int kvm_vcpu_exiting_guest_mode(struct kvm_vcpu *vcpu)
--
1.7.5.4


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