path: root/virt/kvm
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authorMarcelo Tosatti <mtosatti@redhat.com>2012-11-27 23:29:01 -0200
committerMarcelo Tosatti <mtosatti@redhat.com>2012-11-27 23:29:13 -0200
commitd828199e84447795c6669ff0e6c6d55eb9beeff6 (patch)
treec11fc58c50234ddf06f1c4ca98a4115c8fe8ac2f /virt/kvm
parent16e8d74d2da9920f874b10a3d979fb25c01f518f (diff)
KVM: x86: implement PVCLOCK_TSC_STABLE_BIT pvclock flag
KVM added a global variable to guarantee monotonicity in the guest. One of the reasons for that is that the time between 1. ktime_get_ts(&timespec); 2. rdtscll(tsc); Is variable. That is, given a host with stable TSC, suppose that two VCPUs read the same time via ktime_get_ts() above. The time required to execute 2. is not the same on those two instances executing in different VCPUS (cache misses, interrupts...). If the TSC value that is used by the host to interpolate when calculating the monotonic time is the same value used to calculate the tsc_timestamp value stored in the pvclock data structure, and a single <system_timestamp, tsc_timestamp> tuple is visible to all vcpus simultaneously, this problem disappears. See comment on top of pvclock_update_vm_gtod_copy for details. Monotonicity is then guaranteed by synchronicity of the host TSCs and guest TSCs. Set TSC stable pvclock flag in that case, allowing the guest to read clock from userspace. Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Diffstat (limited to 'virt/kvm')
1 files changed, 5 insertions, 0 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e3f5b143158..be3e7bb73b1 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -212,6 +212,11 @@ void kvm_reload_remote_mmus(struct kvm *kvm)
make_all_cpus_request(kvm, KVM_REQ_MMU_RELOAD);
+void kvm_make_mclock_inprogress_request(struct kvm *kvm)
+ make_all_cpus_request(kvm, KVM_REQ_MCLOCK_INPROGRESS);
int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id)
struct page *page;