On 10/31/2011 03:07 PM, Eric B Munson wrote:
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@xxxxxxxxx>
Why not have the guest clear the flag when it acknowledges it?
The hypervisor would unconditionally set the bit, and the guest would do a
testandclear to check if the bit is set. I think that avoids the whole aging
business.
Regards,
Anthony Liguori
---
Cahnges from V1:
Add host functions for flag management to arch/x86/kvm/x86.c instead of
kvmclock.c
arch/x86/include/asm/pvclock.h | 2 ++
arch/x86/kvm/x86.c | 32 ++++++++++++++++++++++++++++++++
include/linux/kvm.h | 2 ++
include/linux/kvm_host.h | 2 ++
4 files changed, 38 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/kvm/x86.c b/arch/x86/kvm/x86.c
index 592ac3b..fb0132a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -46,6 +46,7 @@
#include<linux/hash.h>
#include<linux/pci.h>
#include<trace/events/kvm.h>
+#include<linux/timer.h>
#define CREATE_TRACE_POINTS
#include "trace.h"
@@ -3300,6 +3301,15 @@ 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;
}
@@ -6133,6 +6143,28 @@ void kvm_set_host_stopped(struct kvm_vcpu *vcpu)
}
EXPORT_SYMBOL_GPL(kvm_set_host_stopped);
+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);
+
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 87cab0d..bd9724c 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -765,6 +765,8 @@ struct kvm_clock_data {
#define KVM_ALLOCATE_RMA _IOR(KVMIO, 0xa9, struct kvm_allocate_rma)
/* VM is being stopped by host */
#define KVM_GUEST_PAUSED _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 d526231..043af4d 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -19,6 +19,7 @@
#include<linux/slab.h>
#include<linux/rcupdate.h>
#include<linux/ratelimit.h>
+#include<linux/timer.h>
#include<asm/signal.h>
#include<linux/kvm.h>
@@ -154,6 +155,7 @@ 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)
--
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