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

[Maxime Coquelin <maxime.coquelin@redhat.com>]

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).
> 
>> 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?

Thanks,
Maxime

> Regards,
> Maxime
>