Re: [dpdk-dev] [PATCH v5 3/3] PCI: don't use vfio ioctl call to access PIO resource

["谢华伟(此时此刻）" <huawei.xhw@alibaba-inc.com>]

On 2021/1/13 0:58, Maxime Coquelin wrote:
>
> On 1/12/21 10:37 AM, Maxime Coquelin wrote:
>> bus/pci: ...
>>
>> On 10/22/20 5:51 PM, 谢华伟(此时此刻） wrote:
>>> From: "huawei.xhw" <huawei.xhw@alibaba-inc.com>
>>>
>>> VFIO should use the same way to map/read/write PORT IO as UIO, for
>>> virtio PMD.
>> Please provide more details in the commit message on why the way VFIO
>> works today is wrong (The cover letter is lost once applied).
ok
>>
>>> Signed-off-by: huawei.xhw <huawei.xhw@alibaba-inc.com>
>> Same comment about name format as on previous patches.
>>
>>> ---
>>>   drivers/bus/pci/linux/pci.c     | 8 ++++----
>>>   drivers/bus/pci/linux/pci_uio.c | 4 +++-
>>>   2 files changed, 7 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/bus/pci/linux/pci.c b/drivers/bus/pci/linux/pci.c
>>> index 0dc99e9..2ed9f2b 100644
>>> --- a/drivers/bus/pci/linux/pci.c
>>> +++ b/drivers/bus/pci/linux/pci.c
>>> @@ -687,7 +687,7 @@ int rte_pci_write_config(const struct rte_pci_device *device,
>>>   #ifdef VFIO_PRESENT
>>>   	case RTE_PCI_KDRV_VFIO:
>>>   		if (pci_vfio_is_enabled())
>>> -			ret = pci_vfio_ioport_map(dev, bar, p);
>>> +			ret = pci_uio_ioport_map(dev, bar, p);
>> Doesn't it create a regression with regards to needed capabilities?
>> My understanding is that before this patch we don't need to call iopl(),
>> whereas once applied it is required, correct?
> I did some testing today, and think it is not a regression with para-
> virtualized Virtio devices.
>
> Indeed, I thought it would be a regression with Legacy devices when
> IOMMU is enabled and the program is run as non-root (IOMMU enabled
> just to suport IOVA as VA mode). But it turns out para-virtualized
> Virtio legacy device and vIOMMU enabled is not a supported configuration
> by QEMU.
>
> Note that when noiommu mode is enabled, the app needs cap_sys_rawio, so
> same as iopl(). No regression in this case too.
>
> That said, with real (non para-virtualized) Virtio device using PIO like
> yours, doesn't your patch introduce a restriction for your device that
> it will require cap_sys_rawio whereas it would not be needed?

I don't catch the regression issue.

With real virtio device(hardware implemented), if it is using MMIO, no 
cap_sys_rawio is required.

If it is using PIO, iopl is required always.


> Thanks,
> Maxime
>
>> Regards,
>> Maxime
>>