[PATCH] KVM: x86: fix WARN_ON check of an unsigned less than zero

[PATCH] KVM: x86: fix WARN_ON check of an unsigned less than zero

[Paolo Bonzini]

The check cpu->hv_clock.system_time < 0 is redundant since system_time
is a u64 and hence can never be less than zero.  But what was actually
meant is to check that the result is positive, since kernel_ns and
v->kvm->arch.kvmclock_offset are both s64.

Reported-by: Colin King <colin.king@canonical.com>
Suggested-by: Sean Christopherson <sean.j.christopherson@intel.com>
Addresses-Coverity: ("Macro compares unsigned to 0")
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/x86.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 54e8142b15d0..359fcd395132 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2444,7 +2444,7 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
 	vcpu->hv_clock.tsc_timestamp = tsc_timestamp;
 	vcpu->hv_clock.system_time = kernel_ns + v->kvm->arch.kvmclock_offset;
 	vcpu->last_guest_tsc = tsc_timestamp;
-	WARN_ON(vcpu->hv_clock.system_time < 0);
+	WARN_ON((s64)vcpu->hv_clock.system_time < 0);
 
 	/* If the host uses TSC clocksource, then it is stable */
 	pvclock_flags = 0;
-- 
1.8.3.1

Re: [PATCH] KVM: x86: fix WARN_ON check of an unsigned less than zero

[linmiaohe]

Paolo Bonzini <pbonzini@redhat.com> writes:
> The check cpu->hv_clock.system_time < 0 is redundant since system_time is a u64 and hence can never be less than zero.  But what was actually meant is to check that the result is positive, since kernel_ns and
> v->kvm->arch.kvmclock_offset are both s64.
>
>Reported-by: Colin King <colin.king@canonical.com>
>Suggested-by: Sean Christopherson <sean.j.christopherson@intel.com>
>Addresses-Coverity: ("Macro compares unsigned to 0")
>Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>---

Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>