Re: [Qemu-devel] [PATCH 1/2] qemu kvm: Set up gsi bitmap correctly

[Jan Kiszka]

On 2012-03-27 23:31, Alex Williamson wrote:
> On Tue, 2012-03-27 at 17:00 -0400, Jason Baron wrote:
>> The current 'kvm_init_irq_routing()' doesn't set up the gsi bitmap
>> correctly, and as a consequence pins max_gsi to 32 when it really
>> should be 1024. I ran into this limitation while testing pci
>> passthrough, where I consistently would get -ENOSPACE return from
>> kvm_get_irq_route_gsi() in assigned_dev_update_msix_mmio().
>>
>> Signed-off-by: Jason Baron <address@hidden>
>> ---
>>  kvm-all.c  |    4 ++--
>>  qemu-kvm.c |    2 +-
>>  2 files changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/kvm-all.c b/kvm-all.c
>> index ab88c7c..7d602af 100644
>> --- a/kvm-all.c
>> +++ b/kvm-all.c
>> @@ -873,9 +873,9 @@ static void kvm_init_irq_routing(KVMState *s)
>>          unsigned int gsi_bits, i;
>>  
>>          /* Round up so we can search ints using ffs */
>> -        gsi_bits = (gsi_count + 31) / 32;
>> +        gsi_bits = ALIGN(gsi_count, 32);
>>          s->used_gsi_bitmap = g_malloc0(gsi_bits / 8);
> 
> I think the above is all that's needed (it actually used to be this,
> then got broken in 84b058d).  But if we do this:
> 
>> -        s->max_gsi = gsi_bits;
>> +        s->max_gsi = gsi_count;
> 
> Then we'll hit this assert from the code immediately below where we're
> marking over-allocated bits as already used if we actually did a
> round-up:
> 
> static void set_gsi(KVMState *s, unsigned int gsi)
> {
>     assert(gsi < s->max_gsi);
> 
> Sorry, I had forgotten about this pre-allocation trick to avoid
> returning > gsi_count when we talked about this.

Oh, indeed. That's slightly ugly, gsi_max remains misnamed.

Let's just drop the overeager asserts and keep the number of bitmap
words in KVMState. That's what we really need for doing the work.

Jan

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