Re: [Qemu-devel] [RFC PATCH 06/10] vfio: Allow hotplug of containers onto existing guest IOMMU mappings

[Thomas Huth]

On 18/09/15 01:31, David Gibson wrote:
> On Thu, Sep 17, 2015 at 10:54:24AM -0600, Alex Williamson wrote:
>> On Thu, 2015-09-17 at 23:09 +1000, David Gibson wrote:
>>> At present the memory listener used by vfio to keep host IOMMU mappings
>>> in sync with the guest memory image assumes that if a guest IOMMU
>>> appears, then it has no existing mappings.
>>>
>>> This may not be true if a VFIO device is hotplugged onto a guest bus
>>> which didn't previously include a VFIO device, and which has existing
>>> guest IOMMU mappings.
>>>
>>> Therefore, use the memory_region_register_iommu_notifier_replay()
>>> function in order to fix this case, replaying existing guest IOMMU
>>> mappings, bringing the host IOMMU into sync with the guest IOMMU.
>>>
>>> Signed-off-by: David Gibson <address@hidden>
>>> ---
>>>  hw/vfio/common.c | 34 +++++++++++++++++++---------------
>>>  1 file changed, 19 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
>>> index daaac48..543c38e 100644
>>> --- a/hw/vfio/common.c
>>> +++ b/hw/vfio/common.c
>>> @@ -312,6 +312,22 @@ out:
>>>      rcu_read_unlock();
>>>  }
>>>  
>>> +static hwaddr vfio_container_granularity(VFIOContainer *container)
>>> +{
>>> +    uint64_t pgsize;
>>> +
>>> +    assert(container->iommu_data.iova_pgsizes);
>>
>> return (hwaddr)1 << (ffsl(container->iommu_data.iova_pgsizes) - 1;
> 
> Ah, yes, that should work.  I didn't do it that way mostly because I
> tend to confuse myself when I try to remember exactly how ffs
> semantics work.

Maybe use ffsll instead of ffsl, in case the code ever runs on a 32-bit
host instead of a 64-bit host ?

 Thomas

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