> On 29 Aug 2018, at 13:29, Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote: > > 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;". > > Is the unlikely() really required? I don't know what the fast paths are > in KVM, so I don't know. > > regards, > dan carpenter Why is “min” defined as “int” instead of “unsigned int”? It represents the lowest APIC ID in bitmap so it can’t be negative… "if (unlikely(min > map->max_apic_id || (min + __fls(ipi_bitmap_low)) > map->max_apic_id))” should indeed be ok. -Liran
