On Wed, Aug 29, 2018 at 06:23:08PM +0800, Wanpeng Li wrote: > On Wed, 29 Aug 2018 at 18:18, Dan Carpenter <dan.carpen...@oracle.com> 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;". Is the unlikely() really required? I don't know what the fast paths are in KVM, so I don't know. regards, dan carpenter
