linux-kernel - Re: [RFC] /dev/ioasid uAPI proposal

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Date:   Tue, 1 Jun 2021 13:08:29 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Liu Yi L <yi.l.liu@...ux.intel.com>
Cc:     yi.l.liu@...el.com, "Tian, Kevin" <kevin.tian@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        David Woodhouse <dwmw2@...radead.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Alex Williamson (alex.williamson@...hat.com)\"\"" 
        <alex.williamson@...hat.com>, Eric Auger <eric.auger@...hat.com>,
        Jonathan Corbet <corbet@....net>
Subject: Re: [RFC] /dev/ioasid uAPI proposal


在 2021/6/1 上午11:31, Liu Yi L 写道:
> On Tue, 1 Jun 2021 10:36:36 +0800, Jason Wang wrote:
>
>> 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?
> it's an ID so far in this proposal.


Ok.


>
>> 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?
> oh, missed this question in prior reply. Personally, no special reason
> yet. But using ID may give us opportunity to customize the management
> of the handle. For one, better lookup efficiency by using xarray to
> store the allocated IDs. For two, could categorize the allocated IDs
> (parent or nested). GET_INFO just works with an input FD and an ID.


I'm not sure I get this, for nesting cases you can still make the child 
an fd.

And a question still, under what case we need to create multiple ioasids 
on a single ioasid fd?

(This case is not demonstrated in your examples).

Thanks


>
>>>   
>>>>> 	/* 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.
> good suggestion. :)
>