Re: [Qemu-devel] [PATCH] KVM: Fix GSI number space limit

[Alexander Graf]

On 06.06.14 15:12, Cornelia Huck wrote:
> On Fri,  6 Jun 2014 14:46:05 +0200
> Alexander Graf <address@hidden> wrote:
>
> > KVM tells us the number of GSIs it can handle inside the kernel. That value is
> > basically KVM_MAX_IRQ_ROUTES. However when we try to set the GSI mapping table,
> > it checks for
> >
> >      r = -EINVAL;
> >      if (routing.nr >= KVM_MAX_IRQ_ROUTES)
> >          goto out;
> >
> > erroring out even when we're only using all of the GSIs. To make sure we never
> > hit that limit, let's reduce the number of GSIs we get from KVM by one.
> >
> > Signed-off-by: Alexander Graf <address@hidden>
> > ---
> >   kvm-all.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kvm-all.c b/kvm-all.c
> > index 4e19eff..56a251b 100644
> > --- a/kvm-all.c
> > +++ b/kvm-all.c
> > @@ -938,7 +938,7 @@ void kvm_init_irq_routing(KVMState *s)
> >   {
> >       int gsi_count, i;
> >
> > -    gsi_count = kvm_check_extension(s, KVM_CAP_IRQ_ROUTING);
> > +    gsi_count = kvm_check_extension(s, KVM_CAP_IRQ_ROUTING) - 1;
> >       if (gsi_count > 0) {
> >           unsigned int gsi_bits, i;
> But gsi_count is already marked as used further down in this function,
> isn't it? Confused.

  gsi_bits = ALIGN(gsi_count, 32);
[...]
        for (i = gsi_count; i < gsi_bits; i++) {
            set_gsi(s, i);
        }

So if you take gsi_count = 1024, what happens?

  gsi_count = 1024;
  gsi_bits = 1024;
  for (i = 1024; i < 1024; i++) {
            set_gsi(s, i);
  }

At least in my world of C that loop never runs, no?


Alex