On Wed, Jun 18, 2025 at 01:33:17PM -0700, Sean Christopherson wrote:
> On Wed, Jun 18, 2025, Oliver Upton wrote:
> > > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
>
> No need for my SoB.
>
> > > +#ifdef CONFIG_KVM_GENERIC_PAGE_FAULT
> > > +bool kvm_do_userfault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> >
> > The polarity of the return here feels weird. If we want a value of 0 to
> > indicate success then int is a better return type.
>
> The boolean is my fault/suggestion. My thinking is that it would make the callers
> more intuitive, e.g. so that this reads "if do userfault, then exit to userspace
> with -EFAULT".
>
> if (kvm_do_userfault(vcpu, fault))
> return -EFAULT;
Agreed, this reads correctly. My only issue is that when I read the
function signature, "bool" is usually wired the other way around.
> > > +{
> > > + struct kvm_memory_slot *slot = fault->slot;
> > > + unsigned long __user *user_chunk;
> > > + unsigned long chunk;
> > > + gfn_t offset;
> > > +
> > > + if (!kvm_is_userfault_memslot(slot))
> > > + return false;
> > > +
> > > + offset = fault->gfn - slot->base_gfn;
> > > + user_chunk = slot->userfault_bitmap + (offset / BITS_PER_LONG);
> > > +
> > > + if (__get_user(chunk, user_chunk))
> > > + return true;
>
> And this path is other motiviation for returning a boolean. To me, return "success"
> when a uaccess fails looks all kinds of wrong:
>
> if (__get_user(chunk, user_chunk))
> return 0;
Yeah, that's gross. Although I would imagine we want to express
"failure" here, game over, out to userspace for resolution. So maybe:
if (__get_user(chunk, user_chunk))
return -EFAULT;
> That said, I don't have a super strong preference; normally I'm fanatical about
> not returning booleans. :-D
+1, it isn't _that_ big of a deal, just noticed it as part of review.
Thanks,
Oliver
