On Wed, 29 Aug 2018 at 23:42, Radim Krcmar <rkrcmar@xxxxxxxxxx> wrote: > > 2018-08-29 13:29+0300, Dan Carpenter: > > On Wed, Aug 29, 2018 at 06:23:08PM +0800, Wanpeng Li wrote: > > > On Wed, 29 Aug 2018 at 18:18, Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote: > > > > > > > > On Wed, Aug 29, 2018 at 01:12:05PM +0300, Dan Carpenter wrote: > > > > > On Wed, Aug 29, 2018 at 12:05:06PM +0300, Liran Alon wrote: > > > > > > > arch/x86/kvm/lapic.c | 17 +++++++++++++---- > > > > > > > 1 file changed, 13 insertions(+), 4 deletions(-) > > > > > > > > > > > > > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > > > > > > > index 0cefba2..86e933c 100644 > > > > > > > --- a/arch/x86/kvm/lapic.c > > > > > > > +++ b/arch/x86/kvm/lapic.c > > > > > > > @@ -571,18 +571,27 @@ int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low, > > > > > > > rcu_read_lock(); > > > > > > > map = rcu_dereference(kvm->arch.apic_map); > > > > > > > > > > > > > > + if (unlikely((s32)(map->max_apic_id - __fls(ipi_bitmap_low)) < min)) > > > > > > > + goto out; > > > > > > > > > > > > I personally think “if ((min + __fls(ipi_bitmap_low)) > map->max_apic_id)” is more readable. > > > > > > But that’s just a matter of taste :) > > > > > > > > > > That's an integer overflow. > > > > > > > > > > But I do prefer to put the variable on the left. The truth is that some > > > > > Smatch checks just ignore code which is backwards written because > > > > > otherwise you have to write duplicate code and the most code is written > > > > > with the variable on the left. > > > > > > > > > > if (min > (s32)(map->max_apic_id - __fls(ipi_bitmap_low)) > > > > > > > > Wait, the (s32) cast doesn't make sense. We want negative min values to > > > > be treated as invalid. > > > > > > In v2, how about: > > > > > > if (unlikely(min > map->max_apic_id || (min + __fls(ipi_bitmap_low)) > > > > map->max_apic_id)) > > > goto out; > > > > That works, too. It still has the off by one and we should set > > "count = -KVM_EINVAL;". > > I'd prefer to ignore destinations that are not present and deliver the > rest, possibly nothing, instead of returning an error. > (It's closer to how the real hardware behaves and we already return the > number of notified VCPUs, so the caller can tell whether something went > wrong.) > > Either in the form that I have posted earlier, or as: > > if (min > map->max_apic_id) > goto out; > > for_each_set_bit(i, &ipi_bitmap_low, MIN(BITS_PER_LONG, map->max_apic_id - min + 1)) Do it in v2. Regards, Wanpeng Li
