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([2001:b07:add:ec09:c399:bc87:7b6c:fb2a]) by smtp.googlemail.com with ESMTPSA id b73sm1091762edf.37.2021.12.17.00.45.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 17 Dec 2021 00:45:17 -0800 (PST) Message-ID: Date: Fri, 17 Dec 2021 09:44:55 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: [PATCH] KVM: x86: Use div64_ul instead of do_div Content-Language: en-US To: cgel.zte@gmail.com Cc: seanjc@google.com, vkuznets@redhat.com, wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Changcheng Deng , Zeal Robot References: <20211217084155.452262-1-deng.changcheng@zte.com.cn> From: Paolo Bonzini In-Reply-To: <20211217084155.452262-1-deng.changcheng@zte.com.cn> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/17/21 09:41, cgel.zte@gmail.com wrote: > From: Changcheng Deng > > do_div() does a 64-by-32 division. Here the divisor is an unsigned long > which on some platforms is 64 bit wide. So use div64_ul instead of do_div > to avoid a possible truncation. > > Reported-by: Zeal Robot > Signed-off-by: Changcheng Deng > --- > arch/x86/kvm/lapic.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index c5028e6b0f96..3b629870632c 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -1707,7 +1707,7 @@ static void start_sw_tscdeadline(struct kvm_lapic *apic) > guest_tsc = kvm_read_l1_tsc(vcpu, rdtsc()); > > ns = (tscdeadline - guest_tsc) * 1000000ULL; > - do_div(ns, this_tsc_khz); > + ns = div64_ul(ns, this_tsc_khz); > > if (likely(tscdeadline > guest_tsc) && > likely(ns > apic->lapic_timer.timer_advance_ns)) { > You could change this_tsc_khz to u32 instead, it's assigned from a 32-bit value. Using div64_ul would be unnecessary and less efficient. Paolo