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authorGlauber Costa <glommer@redhat.com>2010-02-01 16:54:05 -0200
committerGreg Kroah-Hartman <gregkh@suse.de>2010-02-09 04:50:56 -0800
commit4f7d6662c57dbaa6be09cc0bad2c01d005638a4d (patch)
treeb0ad11a70fc0aae87001c29e1996156ab5e2526e /arch
parenta74e62c2ef1fda92ad697556261b0e00fee5d581 (diff)
downloadlinux-linaro-stable-4f7d6662c57dbaa6be09cc0bad2c01d005638a4d.tar.gz
KVM: allow userspace to adjust kvmclock offset
(cherry picked from afbcf7ab8d1bc8c2d04792f6d9e786e0adeb328d) When we migrate a kvm guest that uses pvclock between two hosts, we may suffer a large skew. This is because there can be significant differences between the monotonic clock of the hosts involved. When a new host with a much larger monotonic time starts running the guest, the view of time will be significantly impacted. Situation is much worse when we do the opposite, and migrate to a host with a smaller monotonic clock. This proposed ioctl will allow userspace to inform us what is the monotonic clock value in the source host, so we can keep the time skew short, and more importantly, never goes backwards. Userspace may also need to trigger the current data, since from the first migration onwards, it won't be reflected by a simple call to clock_gettime() anymore. [marcelo: future-proof abi with a flags field] [jan: fix KVM_GET_CLOCK by clearing flags field instead of checking it] Signed-off-by: Glauber Costa <glommer@redhat.com> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com> Signed-off-by: Avi Kivity <avi@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/include/asm/kvm_host.h1
-rw-r--r--arch/x86/kvm/x86.c42
2 files changed, 42 insertions, 1 deletions
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index d83892226f73..d759a1f55084 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -412,6 +412,7 @@ struct kvm_arch{
unsigned long irq_sources_bitmap;
unsigned long irq_states[KVM_IOAPIC_NUM_PINS];
u64 vm_init_tsc;
+ s64 kvmclock_offset;
};
struct kvm_vm_stat {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6378e0742691..145741c979bf 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -680,7 +680,8 @@ static void kvm_write_guest_time(struct kvm_vcpu *v)
/* With all the info we got, fill in the values */
vcpu->hv_clock.system_time = ts.tv_nsec +
- (NSEC_PER_SEC * (u64)ts.tv_sec);
+ (NSEC_PER_SEC * (u64)ts.tv_sec) + v->kvm->arch.kvmclock_offset;
+
/*
* The interface expects us to write an even number signaling that the
* update is finished. Since the guest won't see the intermediate
@@ -1227,6 +1228,7 @@ int kvm_dev_ioctl_check_extension(long ext)
case KVM_CAP_PIT2:
case KVM_CAP_PIT_STATE2:
case KVM_CAP_SET_IDENTITY_MAP_ADDR:
+ case KVM_CAP_ADJUST_CLOCK:
r = 1;
break;
case KVM_CAP_COALESCED_MMIO:
@@ -2424,6 +2426,44 @@ long kvm_arch_vm_ioctl(struct file *filp,
r = 0;
break;
}
+ case KVM_SET_CLOCK: {
+ struct timespec now;
+ struct kvm_clock_data user_ns;
+ u64 now_ns;
+ s64 delta;
+
+ r = -EFAULT;
+ if (copy_from_user(&user_ns, argp, sizeof(user_ns)))
+ goto out;
+
+ r = -EINVAL;
+ if (user_ns.flags)
+ goto out;
+
+ r = 0;
+ ktime_get_ts(&now);
+ now_ns = timespec_to_ns(&now);
+ delta = user_ns.clock - now_ns;
+ kvm->arch.kvmclock_offset = delta;
+ break;
+ }
+ case KVM_GET_CLOCK: {
+ struct timespec now;
+ struct kvm_clock_data user_ns;
+ u64 now_ns;
+
+ ktime_get_ts(&now);
+ now_ns = timespec_to_ns(&now);
+ user_ns.clock = kvm->arch.kvmclock_offset + now_ns;
+ user_ns.flags = 0;
+
+ r = -EFAULT;
+ if (copy_to_user(argp, &user_ns, sizeof(user_ns)))
+ goto out;
+ r = 0;
+ break;
+ }
+
default:
;
}