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

[Santosh Shukla <sshukla@mvista.com>]

On Thu, Jan 21, 2016 at 4:58 PM, Thomas Monjalon
<thomas.monjalon@6wind.com> wrote:
> 2016-01-21 16:43, Santosh Shukla:
>> David Marchand <david.marchand@6wind.com> wrote:
>> > This is a mode (specific to vfio), not a new kernel driver.
>> >
>> Yes, Specific to VFIO and this is why noiommu appended after vfio i.e..
>> __VFIO and __VFIO_NOIOMMU.
>
> Woaaa! Your logic is really disappointing :)
> Specific to VFIO => append _NOIOMMU
> If it's for VFIO, it should be called VFIO (that's my logic).
>
I am confused by reading your comment. vfio works for default iommu
and now with noiommu. drv->kdrv need to know driver mode for vfio
case. So that user can simply read drv->kdrv value in their driver and
accordingly use vfio rd/wr api for example {pread/pwrite}. This is how
rte_eal_pci_vfio_read/write_bar() api implemented.

And Yes it is called VFIO but with with specifics appended in it.

>> > How come we need to distinguish between with/without iommu modes ?
>>
>> By default vfio framework assumes iommu i.,e., iommu present. Unless user
>> explicitly set "enable_unsafe_noiommu_mode" param. so in my opinion, we
>> care to parse vfio driver for _noiommu_ mode only.
>
> Why do we care to parse noiommu only?

Because pmd drivers example virtio can work with vfio only in
_noiommu_ mode. In particular, virtio spec 0.95 / legacy virtio. So at
the initialization (example .. virtio-net) of such pmd driver, pmd
driver should know that vfio-with-noiommu mode enabled or not? for
that pmd driver simply checks drv->kdrv value. Currently virtio-net
pmd driver does resource parsing then resource init for interfaces
like UIO/ioport, I intend to do same but only parsing, as resource
init for vfio case already taken care by pci_xx_vfio_map() api in
virtio-net pmd driver (refer Yaun recently virtio 1.0 recently
submitted rte_eal_pci_map patch)

Also Yuan in one of earlier thread inclined to remove all the resource
parsing api from virtio-net pmd driver. Pl. refer this thread [1]

[1] http://dpdk.org/dev/patchwork/patch/9862/

> Even if virtio cannot work in an IOMMU case, there is no reason to add
> a VFIO_NOIOMMU type here.
>
>> > Should not vfio behave the same way from an api point of view ?
>> >
>> Yes It should. vfio gives similar file_ops i.e.. read/write/mmap/seek etc..
>> I am little confused on your question, do you see any issue in vfio bar
>> rd/wr api implementation?
>
> I think you should just consider the VFIO API and let the noiommu option
> as a kernel configuration detail.

vfio apis _are_ considered at low level rd/wr implementation, Has
nothing to do with iommu/noiommu mode. See pci_vfio_read/write_bar()
implementation, they are using pread64/pwrite64() vfio rd/wr api.