Re: [RFC] /dev/ioasid uAPI proposal

[Jason Wang]

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


>