Re: [PATCH] vfio-pci: Use io_remap_pfn_range() for PCI IO memory

[Tom Lendacky <thomas.lendacky@amd.com>]

On 11/16/20 9:53 AM, Jason Gunthorpe wrote:
> On Thu, Nov 05, 2020 at 06:39:49PM -0500, Peter Xu wrote:
>> On Thu, Nov 05, 2020 at 12:34:58PM -0400, Jason Gunthorpe wrote:
>>> Tom says VFIO device assignment works OK with KVM, so I expect only things
>>> like DPDK to be broken.
>>
>> Is there more information on why the difference?  Thanks,
> 
> I have nothing, maybe Tom can explain how it works?

IIUC, the main differences would be along the lines of what is performing
the mappings or who is performing the MMIO.

For device passthrough using VFIO, the guest kernel is the one that ends
up performing the MMIO in kernel space with the proper encryption mask
(unencrypted).

I'm not familiar with how DPDK really works other than it is userspace
based and uses polling drivers, etc. So it all depends on how everything
gets mapped and by whom. For example, using mmap() to get a mapping to
something that should be mapped unencrypted will be an issue since the
userspace mappings are created encrypted. Extending mmap() to be able to
specify a new flag, maybe MAP_UNENCRYPTED, might be something to consider.

Thanks,
Tom

> 
> Jason 
>