Messages in this thread | | | Date | Fri, 17 Dec 2021 09:44:55 +0100 | Subject | Re: [PATCH] KVM: x86: Use div64_ul instead of do_div | From | Paolo Bonzini <> |
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On 12/17/21 09:41, cgel.zte@gmail.com wrote: > From: Changcheng Deng <deng.changcheng@zte.com.cn> > > 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 <zealci@zte.com.cn> > Signed-off-by: Changcheng Deng <deng.changcheng@zte.com.cn> > --- > 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
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