Re: [RFC] /dev/ioasid uAPI proposal

Jason Wang
2021-06-01T02:36:52Z

在 2021/5/31 下午4:41, Liu Yi L 写道:
>> I guess VFIO_ATTACH_IOASID will fail if the underlayer doesn't support
>> hardware nesting. Or is there way to detect the capability before?
> I think it could fail in the IOASID_CREATE_NESTING. If the gpa_ioasid
> is not able to support nesting, then should fail it.
>
>> I think GET_INFO only works after the ATTACH.
> yes. After attaching to gpa_ioasid, userspace could GET_INFO on the
> gpa_ioasid and check if nesting is supported or not. right?

Some more questions:

1) Is the handle returned by IOASID_ALLOC an fd?
2) If yes, what's the reason for not simply use the fd opened from
/dev/ioas. (This is the question that is not answered) and what happens
if we call GET_INFO for the ioasid_fd?
3) If not, how GET_INFO work?

>
>>> /* Bind guest I/O page table */
>>> bind_data = {
>>> .ioasid = giova_ioasid;
>>> .addr = giova_pgtable;
>>> // and format information
>>> };
>>> ioctl(ioasid_fd, IOASID_BIND_PGTABLE, &bind_data);
>>>
>>> /* Invalidate IOTLB when required */
>>> inv_data = {
>>> .ioasid = giova_ioasid;
>>> // granular information
>>> };
>>> ioctl(ioasid_fd, IOASID_INVALIDATE_CACHE, &inv_data);
>>>
>>> /* See 5.6 for I/O page fault handling */
>>>
>>> 5.5. Guest SVA (vSVA)
>>> ++++++++++++++++++
>>>
>>> After boots the guest further create a GVA address spaces (gpasid1) on
>>> dev1. Dev2 is not affected (still attached to giova_ioasid).
>>>
>>> As explained in section 4, user should avoid expose ENQCMD on both
>>> pdev and mdev.
>>>
>>> The sequence applies to all device types (being pdev or mdev), except
>>> one additional step to call KVM for ENQCMD-capable mdev:
>> My understanding is ENQCMD is Intel specific and not a requirement for
>> having vSVA.
> ENQCMD is not really Intel specific although only Intel supports it today.
> The PCIe DMWr capability is the capability for software to enumerate the
> ENQCMD support in device side. yes, it is not a requirement for vSVA. They
> are orthogonal.

Right, then it's better to mention DMWr instead of a vendor specific
instruction in a general framework like ioasid.

Thanks

>