> -----Original Message----- > From: kvm-ppc-owner@xxxxxxxxxxxxxxx > [mailto:kvm-ppc-owner@xxxxxxxxxxxxxxx] On Behalf Of Bharat Bhushan > Sent: Wednesday, October 19, 2011 12:16 PM > To: agraf@xxxxxxx > Cc: kvm-ppc@xxxxxxxxxxxxxxx; bharatb.yadav@xxxxxxxxx; Bhushan > Bharat-R65777 > Subject: [PATCH v2] Fix DEC truncation for greater than > 0xffff_ffff/1000 > > kvmppc_emulate_dec() uses dec_nsec of type unsigned long and > does below calculation: > > dec_nsec = vcpu->arch.dec; > dec_nsec *= 1000; > This will truncate if DEC value "vcpu->arch.dec" is greater > than 0xffff_ffff/1000. > For example : For tb_ticks_per_usec = 4a, we can not set > decrementer more than ~58ms. > > Signed-off-by: Bharat Bhushan <bharat.bhushan@xxxxxxxxxxxxx> > --- > arch/powerpc/kvm/emulate.c | 12 +++++++----- > 1 files changed, 7 insertions(+), 5 deletions(-) > > diff --git a/arch/powerpc/kvm/emulate.c b/arch/powerpc/kvm/emulate.c > index 8af3bad..e7f3da4 100644 > --- a/arch/powerpc/kvm/emulate.c > +++ b/arch/powerpc/kvm/emulate.c > @@ -84,6 +84,7 @@ static bool kvmppc_dec_enabled(struct > kvm_vcpu *vcpu) > void kvmppc_emulate_dec(struct kvm_vcpu *vcpu) > { > unsigned long dec_nsec; > + unsigned long long dec_time; > > pr_debug("mtDEC: %x\n", vcpu->arch.dec); > #ifdef CONFIG_PPC_BOOK3S > @@ -103,11 +104,12 @@ void kvmppc_emulate_dec(struct kvm_vcpu *vcpu) > * host ticks. */ > > hrtimer_try_to_cancel(&vcpu->arch.dec_timer); > - dec_nsec = vcpu->arch.dec; > - dec_nsec *= 1000; > - dec_nsec /= tb_ticks_per_usec; > - hrtimer_start(&vcpu->arch.dec_timer, > ktime_set(0, dec_nsec), > - HRTIMER_MODE_REL); > + dec_time = vcpu->arch.dec; > + dec_time *= 1000; > + do_div(dec_time, tb_ticks_per_usec); > + dec_nsec = do_div(dec_time, NSEC_PER_SEC); > + hrtimer_start(&vcpu->arch.dec_timer, > + ktime_set(dec_time, dec_nsec), > HRTIMER_MODE_REL); > vcpu->arch.dec_jiffies = get_tb(); > } else { > hrtimer_try_to_cancel(&vcpu->arch.dec_timer); > -- > 1.7.0.4 > How does this impact performance? 64bits multiplication and division looks slow. Thanks, Yu -- To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
