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

From: Paolo Bonzini <pbonzini@redhat.com>
To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: colin.king@canonical.com, sean.j.christopherson@intel.com
Subject: [PATCH] KVM: x86: fix WARN_ON check of an unsigned less than zero
Date: Wed, 12 Feb 2020 13:28:48 +0100	[thread overview]
Message-ID: <1581510528-19303-1-git-send-email-pbonzini@redhat.com> (raw)

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

