[dpdk-dev] [PATCH] bus/pci: forbid VA as IOVA mode if IOMMU address width too small

[Maxime Coquelin]

On 01/08/2018 04:34 PM, Stephen Hemminger wrote:
> On Mon,  8 Jan 2018 14:51:27 +0100
> Maxime Coquelin <maxime.coquelin at redhat.com> wrote:
> 
>> Intel VT-d supports different address widths for the IOVAs, from
>> 39 bits to 56 bits.
>>
>> While recent processors support at least 48 bits, VT-d emulation
>> currently only supports 39 bits. It makes DMA mapping to fail in this
>> case when using VA as IOVA mode, as user-space virtual addresses uses
>> up to 47 bits (see kernel's Documentation/x86/x86_64/mm.txt).
>>
>> This patch parses VT-d CAP register value available in sysfs, and
>> forbid VA as IOVA mode if the GAW is 39 bits or unknown.
>>
>> Fixes: f37dfab21c98 ("drivers/net: enable IOVA mode for Intel PMDs")
>>
>> Cc: stable at dpdk.org
>> Signed-off-by: Maxime Coquelin <maxime.coquelin at redhat.com>
>> ---
>> Hi,
>>
>> I'm not super happy with the patch as it does platform specific things in
>> generic code, but there are no placeholder for IOMMU/VT-d at the moment.
>>
>> As this patch is to be backported to v17.11 LTS, it cannot be a big rework.
>>
>> If you have some suggestion to improve it, please let me know.
>>
>> The fix is quite urgent, as guest device assignment with vIOMMU is broken in
>> mainline & v17.11 LTS.
>>
>> Advantage of this fix over forbidding VA as IOVA when running in emulation is
>> that VT-d emulation will soon support 48 bits, so this is future proof. Also,
>> VT-d spec supports 39 bits, so we could have physical CPUs supporting it, even
>> if I don't know any.
>>
>> Thanks,
>> Maxime
> 
> You are assumming that if IOMMU is present that it is being used (ie VFIO).
> What about the case of direct access to PF device via IGB_UIO?

As soon as one device is bound to UIO or VFIO in noiomu mode, PA as IOVA
mode will be selected.

This is done in rte_pci_get_iommu_class(), by calling
pci_one_device_bound_uio() and rte_vfio_noiommu_is_enabled().

>> +static inline bool
>> +pci_one_device_iommu_support_va(struct rte_pci_device *dev)
>> +{
> 
> This is not in fast path, there is no reason it should be inline
> 

Ok, I will remove inlining in v2. I added it for consistency with the
other functions declared above.

Thanks,
Maxime