KVM: VMX: initialize TSC offset relative to vm creation time
VMX initializes the TSC offset for each vcpu at different times, and
also reinitializes it for vcpus other than 0 on APIC SIPI message.
This bug causes the TSC's to appear unsynchronized in the guest, even if
the host is good.
Older Linux kernels don't handle the situation very well, so
gettimeofday is likely to go backwards in time:
http://www.mail-archive.com/kvm@vger.kernel.org/msg02955.html
http://sourceforge.net/tracker/index.php?func=detail&aid=2025534&group_id=180599&atid=893831
Fix it by initializating the offset of each vcpu relative to vm creation
time, and moving it from vmx_vcpu_reset to vmx_vcpu_setup, out of the
APIC MP init path.
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index cee81c9..3312047 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -865,11 +865,8 @@
* writes 'guest_tsc' into guest's timestamp counter "register"
* guest_tsc = host_tsc + tsc_offset ==> tsc_offset = guest_tsc - host_tsc
*/
-static void guest_write_tsc(u64 guest_tsc)
+static void guest_write_tsc(u64 guest_tsc, u64 host_tsc)
{
- u64 host_tsc;
-
- rdtscll(host_tsc);
vmcs_write64(TSC_OFFSET, guest_tsc - host_tsc);
}
@@ -934,6 +931,7 @@
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
struct kvm_msr_entry *msr;
+ u64 host_tsc;
int ret = 0;
switch (msr_index) {
@@ -959,7 +957,8 @@
vmcs_writel(GUEST_SYSENTER_ESP, data);
break;
case MSR_IA32_TIME_STAMP_COUNTER:
- guest_write_tsc(data);
+ rdtscll(host_tsc);
+ guest_write_tsc(data, host_tsc);
break;
case MSR_P6_PERFCTR0:
case MSR_P6_PERFCTR1:
@@ -2109,7 +2108,7 @@
{
u32 host_sysenter_cs, msr_low, msr_high;
u32 junk;
- u64 host_pat;
+ u64 host_pat, tsc_this, tsc_base;
unsigned long a;
struct descriptor_table dt;
int i;
@@ -2237,6 +2236,12 @@
vmcs_writel(CR0_GUEST_HOST_MASK, ~0UL);
vmcs_writel(CR4_GUEST_HOST_MASK, KVM_GUEST_CR4_MASK);
+ tsc_base = vmx->vcpu.kvm->arch.vm_init_tsc;
+ rdtscll(tsc_this);
+ if (tsc_this < vmx->vcpu.kvm->arch.vm_init_tsc)
+ tsc_base = tsc_this;
+
+ guest_write_tsc(0, tsc_base);
return 0;
}
@@ -2328,8 +2333,6 @@
vmcs_write32(GUEST_INTERRUPTIBILITY_INFO, 0);
vmcs_write32(GUEST_PENDING_DBG_EXCEPTIONS, 0);
- guest_write_tsc(0);
-
/* Special registers */
vmcs_write64(GUEST_IA32_DEBUGCTL, 0);