KVM: x86: retain pvclock guest stopped bit in guest memory

Otherwise its possible for an unrelated KVM_REQ_UPDATE_CLOCK (such as due to CPU
migration) to clear the bit.

Noticed by Paolo Bonzini.

Reviewed-by: Gleb Natapov <gleb@redhat.com>
Reviewed-by: Glauber Costa <glommer@parallels.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c31f75dd24d4720f98cfcc65e0328884767be79b..1dfe9d318734a47297005c6d322242145fb633e0 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1145,6 +1145,7 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
        unsigned long this_tsc_khz;
        s64 kernel_ns, max_kernel_ns;
        u64 tsc_timestamp;
+       struct pvclock_vcpu_time_info *guest_hv_clock;
        u8 pvclock_flags;
 
        /* Keep irq disabled to prevent changes to the clock */
@@ -1228,13 +1229,6 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
        vcpu->last_kernel_ns = kernel_ns;
        vcpu->last_guest_tsc = tsc_timestamp;
 
-       pvclock_flags = 0;
-       if (vcpu->pvclock_set_guest_stopped_request) {
-               pvclock_flags |= PVCLOCK_GUEST_STOPPED;
-               vcpu->pvclock_set_guest_stopped_request = false;
-       }
-
-       vcpu->hv_clock.flags = pvclock_flags;
 
        /*
         * The interface expects us to write an even number signaling that the
@@ -1245,6 +1239,18 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
 
        shared_kaddr = kmap_atomic(vcpu->time_page);
 
+       guest_hv_clock = shared_kaddr + vcpu->time_offset;
+
+       /* retain PVCLOCK_GUEST_STOPPED if set in guest copy */
+       pvclock_flags = (guest_hv_clock->flags & PVCLOCK_GUEST_STOPPED);
+
+       if (vcpu->pvclock_set_guest_stopped_request) {
+               pvclock_flags |= PVCLOCK_GUEST_STOPPED;
+               vcpu->pvclock_set_guest_stopped_request = false;
+       }
+
+       vcpu->hv_clock.flags = pvclock_flags;
+
        memcpy(shared_kaddr + vcpu->time_offset, &vcpu->hv_clock,
               sizeof(vcpu->hv_clock));