[dpdk-dev] [PATCH v6 08/11] eal: pci: introduce RTE_KDRV_VFIO_NOIOMMUi driver mode

[Santosh Shukla]

On Tue, Jan 26, 2016 at 9:51 PM, Santosh Shukla <sshukla at mvista.com> wrote:
> On Tue, Jan 26, 2016 at 7:58 PM, Thomas Monjalon
> <thomas.monjalon at 6wind.com> wrote:
>> 2016-01-26 19:35, Santosh Shukla:
>>> On Tue, Jan 26, 2016 at 6:30 PM, Thomas Monjalon
>>> <thomas.monjalon at 6wind.com> wrote:
>>> > 2016-01-26 15:56, Santosh Shukla:
>>> >> In my observation, currently virtio work for vfio-noiommu, that's why
>>> >> said drv->kdrv need to know vfio mode.
>>> >
>>> > It is your observation. It may change in near future.
>>>
>>> so that mean till then, virtio support for non-x86 arch has to wait?
>>
>> No, absolutely not. virtio for non-x86 is welcome.
>>
>>> We have working model with vfio-noiommu, don't you think it make sense
>>> to let vfio_noiommu implementation exist and later in-case
>>> virtio+iommu gets mainline then switch to vfio __mode__ agnostic
>>> approach. And for that All it takes to replace __noiommu suffix with
>>> default.
>>
>> I'm just saying you should not touch the enum rte_kernel_driver.
>> RTE_KDRV_VFIO is a driver.
>> RTE_KDRV_VFIO_NOIOMMU is a mode.
>> As the VFIO API is the same in both modes, there is no reason to
>> distinguish them at this level.
>> Your patch adds the NOIOMMU case everywhere:
>>         case RTE_KDRV_VFIO:
>> +       case RTE_KDRV_VFIO_NOIOMMU:
>>
>> I'll stop commenting here to let others give their opinion.
>>
>> [...]
>>> >> with vfio+iommu; binding virtio pci device to vfio-pci driver fail;
>>> >> giving below error:
>>> >> [   53.053464] VFIO - User Level meta-driver version: 0.3
>>> >> [   73.077805] vfio-pci: probe of 0000:00:03.0 failed with error -22
>>> >> [   73.077852] vfio-pci: probe of 0000:00:03.0 failed with error -22
>>> >>
>>> >> vfio_pci_probe() --> vfio_iommu_group_get() --> iommu_group_get()
>>> >> fails: iommu doesn't have group for virtio pci device.
>>> >
>>> > Yes it fails when binding.
>>> > So the later check in the virtio PMD is useless.
>>>
>>> Which check?
>>
>> The check for VFIO noiommu only:
>> -       if (dev->kdrv == RTE_KDRV_VFIO)
>> +       if (dev->kdrv == RTE_KDRV_VFIO_NOIOMMU)
>>
>> [...]
>>> > Furthermore restricting virtio to no-iommu mode doesn't bring
>>> > any improvement.
>>>
>>> We're not __restricting__, as soon as virtio+iommu gets working state,
>>> we'll simply replace __noiommu with default. Then its upto user to try
>>> out virtio with vfio default or vfio_noiommu.
>>
>> Yes it's up to user.
>> So your code should be
>>         if (dev->kdrv == RTE_KDRV_VFIO)
>>
>
> Right,
>
>>> > That's why I suggest to keep the initial semantic of kdrv and
>>> > not pollute it with VFIO modes.
>>>
>>> I am okay to live with default and forget suffix __noiommu but there
>>> are implementation problem which was discussed in other thread
>>> - Virtio pmd driver should avoid interface parsing i.e.
>>> virtio_resource_init_uio/vfio() etc.. For vfio case - We could easily
>>> get rid of by moving /sys parsing to pci_eal layer, Right? If so then
>>> virtio currently works with vfio-noiommu, it make sense to me that
>>> pci_eal layer does parsing for pmd driver before that pmd driver get
>>> initialized.
>>
>> Please reword. What is the problem?
>>
>>> - Another case could be: iommu-less-pmd-driver. eal layer to do
>>> parsing before updating drv->kdrv.
>>
>> [...]
>>> >> >> > If a check is needed, I would prefer using your function
>>> >> >> > pci_vfio_is_noiommu() and remove driver modes from struct rte_kernel_driver.
>>> >> >>
>>> >> >> I don't think calling pci_vfio_no_iommu() inside
>>> >> >> virtio_reg_rd/wr_1/2/3() would be a good idea.
>>> >> >
>>> >> > Why? The value may be cached in the priv properties.
>>> >> >
>>> >> pci_vfio_is_noiommu() parses /sys for
>>> >> - enable_noiommu param
>>> >> - attached driver name is vfio-noiommu or not.
>>> >>
>>> >> It does file operation for that, I meant to say that calling this api
>>> >> within register_rd/wr function is not correct. It would be better if
>>> >> those low level register_rd/wr api only checks driver_types.
>>> >
>>> > Yes, that's why I said the return of pci_vfio_is_noiommu() may be cached
>>> > to keep efficiency.
>>>
>>> I am not convinced though, Still find pmd driver checking driver_types
>>> using drv->kdrv is better approach than introducing a new global
>>> variable which may look something like;
>>
>> Not a global variable. A function in EAL layer. A variable in PMD priv.
>>
>
> If we agreed to use condition (drv->kdrv == RTE_KDRV_VFIO);
> then resource parsing for vfio {including vfio and vfio_noiommu both
> case} is enforced in virtio pmd driver layer and that is contradicting
> to what we agreed earlier in this[1] thread. Also we don't need a
> function in EAL layer or a variable in PMD priv. Perhaps a private
> function in virtio pmd which does parsing for vfio interface.
>
> Thoughts?
>
> [1] http://dpdk.org/dev/patchwork/patch/9862/
>

Any comment/feedback on above approach?

>>> At pci_eal layer ----
>>> bool vfio_mode;
>>> vfio_mode = pci_vfio_is_noiommu();
>>>
>>> At virtio pmd driver layer ----
>>> Checking value at vfio_mode variable before doing virtio_rd/wr for
>>> vfio interface.
>>>
>>> Instead virtio pmd driver doing
>>>
>>> virtio_reg_rd/wr_1/2/4()
>>> {
>>> if (drv->kdrv == VFIO)
>>>       do pread()/pwrite()
>>> else
>>>       in()/out()
>>> }
>>>
>>> is better approach.
>>>
>>> Let me know if you still think former is better than latter then I'll
>>> send patch revision right-away.
>>
>>