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([2001:b07:6468:f312:652c:29a6:517b:66d9]) by smtp.gmail.com with ESMTPSA id l15sm453755wrv.39.2020.02.12.04.32.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 12 Feb 2020 04:32:01 -0800 (PST) Subject: Re: [PATCH][next] KVM: x86: remove redundant WARN_ON check of an unsigned less than zero To: Sean Christopherson , Colin King Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H . Peter Anvin" , x86@kernel.org, kvm@vger.kernel.org, kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org References: <20200207231813.786224-1-colin.king@canonical.com> <20200208004722.GB15581@linux.intel.com> From: Paolo Bonzini Message-ID: <21975038-ae1a-50a1-7fa0-38a1445abe8d@redhat.com> Date: Wed, 12 Feb 2020 13:32:06 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <20200208004722.GB15581@linux.intel.com> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/02/20 01:47, Sean Christopherson wrote: > On Fri, Feb 07, 2020 at 11:18:13PM +0000, Colin King wrote: >> From: Colin Ian King >> >> The check cpu->hv_clock.system_time < 0 is redundant since system_time >> is a u64 and hence can never be less than zero. Remove it. >> >> Addresses-Coverity: ("Macro compares unsigned to 0") >> Signed-off-by: Colin Ian King >> --- >> arch/x86/kvm/x86.c | 1 - >> 1 file changed, 1 deletion(-) >> >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index fbabb2f06273..d4967ac47e68 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -2448,7 +2448,6 @@ 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); > > Don't know this code well, but @kernel_ns and @v->kvm->arch.kvmclock_offset > are both s64, so maybe this was intended and/or desirable? > > WARN_ON((s64)vcpu->hv_clock.system_time < 0); Yes, that's related to the bugfix where kvmclock would get negative. I queued the patch with the (s64) cast added. Thanks to both of you! Paolo