* [PATCH] KVM: x86: Use div64_ul instead of do_div
@ 2021-12-17 8:41 cgel.zte
2021-12-17 8:44 ` Paolo Bonzini
0 siblings, 1 reply; 2+ messages in thread
From: cgel.zte @ 2021-12-17 8:41 UTC (permalink / raw)
To: pbonzini
Cc: seanjc, vkuznets, wanpengli, jmattson, joro, tglx, mingo, bp,
dave.hansen, x86, hpa, kvm, linux-kernel, Changcheng Deng,
Zeal Robot
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)) {
--
2.25.1
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH] KVM: x86: Use div64_ul instead of do_div
2021-12-17 8:41 [PATCH] KVM: x86: Use div64_ul instead of do_div cgel.zte
@ 2021-12-17 8:44 ` Paolo Bonzini
0 siblings, 0 replies; 2+ messages in thread
From: Paolo Bonzini @ 2021-12-17 8:44 UTC (permalink / raw)
To: cgel.zte
Cc: seanjc, vkuznets, wanpengli, jmattson, joro, tglx, mingo, bp,
dave.hansen, x86, hpa, kvm, linux-kernel, Changcheng Deng,
Zeal Robot
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
^ permalink raw reply [flat|nested] 2+ messages in thread
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2021-12-17 8:41 [PATCH] KVM: x86: Use div64_ul instead of do_div cgel.zte
2021-12-17 8:44 ` Paolo Bonzini
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