From: David Laight <David.Laight@ACULAB.COM>
To: "'José Pekkarinen'" <jose.pekkarinen@foxhound.fi>,
"seanjc@google.com" <seanjc@google.com>,
"pbonzini@redhat.com" <pbonzini@redhat.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"mingo@redhat.com" <mingo@redhat.com>,
"bp@alien8.de" <bp@alien8.de>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
"skhan@linuxfoundation.org" <skhan@linuxfoundation.org>
Cc: "x86@kernel.org" <x86@kernel.org>,
"linux-kernel-mentees@lists.linuxfoundation.org"
<linux-kernel-mentees@lists.linuxfoundation.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"hpa@zytor.com" <hpa@zytor.com>
Subject: RE: [PATCH] KVM: x86: replace do_div with div64_ul
Date: Tue, 31 Oct 2023 09:35:23 +0000 [thread overview]
Message-ID: <23f90fd3273a4d7f961b277758ac7af8@AcuMS.aculab.com> (raw)
In-Reply-To: <20231029093928.138570-1-jose.pekkarinen@foxhound.fi>
From: José Pekkarinen
> Sent: 29 October 2023 09:39
>
> Reported by coccinelle, there is a do_div call that does
> 64-by-32 divisions even in 64bit platforms, this patch will
> move it to div64_ul macro that will decide the correct
> division function for the platform underneath. The output
> the warning follows:
>
> arch/x86/kvm/lapic.c:1948:1-7: WARNING: do_div() does a 64-by-32 division, please consider using
> div64_ul instead.
That is about the worst message from the coccinelle scripts.
It really ought to ask you to check the domain on the values.
>
> Signed-off-by: José Pekkarinen <jose.pekkarinen@foxhound.fi>
> ---
> 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 3e977dbbf993..0b90c6ad5091 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1945,7 +1945,7 @@ 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);
> + div64_ul(ns, this_tsc_khz);
Did you test this?
Hint - you didn't.
David
>
> if (likely(tscdeadline > guest_tsc) &&
> likely(ns > apic->lapic_timer.timer_advance_ns)) {
> --
> 2.39.2
-
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prev parent reply other threads:[~2023-10-31 9:42 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-29 9:39 [PATCH] KVM: x86: replace do_div with div64_ul José Pekkarinen
2023-10-30 16:12 ` Sean Christopherson via Linux-kernel-mentees
2023-10-31 9:35 ` David Laight [this message]
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