KVM: x86: Return updated timer current count register from KVM_GET_LAPIC

kvm_vcpu_ioctl_get_lapic (implements KVM_GET_LAPIC ioctl) does a bulk copy
of the LAPIC registers but must take into account that the one-shot and
periodic timer current count register is computed upon reads and is not
present in register state. When restoring LAPIC state (e.g. after
migration), restart timers from their their current count values at time of
save.

Note: When a one-shot timer expires, the code in arch/x86/kvm/lapic.c does
not zero the value of the LAPIC initial count register (emulating HW
behavior). If no other timer is run and pending prior to a subsequent
KVM_GET_LAPIC call, the returned register set will include the expired
one-shot initial count. On a subsequent KVM_SET_LAPIC call the code will
see a non-zero initial count and start a new one-shot timer using the
expired timer's count. This is a prior existing bug and will be addressed
in a separate patch. Thanks to jmattson@google.com for this find.

Signed-off-by: Peter Shier <pshier@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Wanpeng Li <wanpengli@tencent.com>
Message-Id: <20181010225653.238911-1-pshier@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index a0ffb4331418..7f15f9e69efe 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -161,9 +161,14 @@ static inline u32 kvm_lapic_get_reg(struct kvm_lapic *apic, int reg_off)
 	return *((u32 *) (apic->regs + reg_off));
 }
 
+static inline void __kvm_lapic_set_reg(char *regs, int reg_off, u32 val)
+{
+	*((u32 *) (regs + reg_off)) = val;
+}
+
 static inline void kvm_lapic_set_reg(struct kvm_lapic *apic, int reg_off, u32 val)
 {
-	*((u32 *) (apic->regs + reg_off)) = val;
+	__kvm_lapic_set_reg(apic->regs, reg_off, val);
 }
 
 extern struct static_key kvm_no_apic_vcpu;