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

[Alexander Graf <agraf@suse.de>]

On 06.06.14 15:12, Cornelia Huck wrote:
> On Fri,  6 Jun 2014 14:46:05 +0200
> Alexander Graf <agraf@suse.de> 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 <agraf@suse.de>
>> ---
>>   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