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Message-ID: <afacee89-4edb-f4fb-156d-7b6c8dd0bb3b@redhat.com>
Date: Fri, 17 Dec 2021 09:44:55 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: cgel.zte@...il.com
Cc: seanjc@...gle.com, vkuznets@...hat.com, wanpengli@...cent.com,
jmattson@...gle.com, joro@...tes.org, tglx@...utronix.de,
mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
x86@...nel.org, hpa@...or.com, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org,
Changcheng Deng <deng.changcheng@....com.cn>,
Zeal Robot <zealci@....com.cn>
Subject: Re: [PATCH] KVM: x86: Use div64_ul instead of do_div
On 12/17/21 09:41, cgel.zte@...il.com wrote:
> From: Changcheng Deng <deng.changcheng@....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@....com.cn>
> Signed-off-by: Changcheng Deng <deng.changcheng@....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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