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From: Shenming Lu <lushenming@huawei.com>
To: "Tian, Kevin" <kevin.tian@intel.com>,
	Alex Williamson <alex.williamson@redhat.com>
Cc: Cornelia Huck <cohuck@redhat.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Jean-Philippe Brucker <jean-philippe@linaro.org>,
	Eric Auger <eric.auger@redhat.com>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	"wanghaibin.wang@huawei.com" <wanghaibin.wang@huawei.com>,
	"yuzenghui@huawei.com" <yuzenghui@huawei.com>,
	"Liu, Yi L" <yi.l.liu@intel.com>,
	"Pan, Jacob jun" <jacob.jun.pan@intel.com>
Subject: Re: [RFC PATCH v1 0/4] vfio: Add IOPF support for VFIO passthrough
Date: Thu, 18 Mar 2021 20:47:16 +0800	[thread overview]
Message-ID: <4e2c9f05-9a87-4aca-71d3-c329d7638aae@huawei.com> (raw)
In-Reply-To: <MWHPR11MB1886498515951BCE98F9336A8C699@MWHPR11MB1886.namprd11.prod.outlook.com>

On 2021/3/18 20:32, Tian, Kevin wrote:
>> From: Shenming Lu <lushenming@huawei.com>
>> Sent: Thursday, March 18, 2021 7:54 PM
>> On 2021/3/18 17:07, Tian, Kevin wrote:
>>>> From: Shenming Lu <lushenming@huawei.com>
>>>> Sent: Thursday, March 18, 2021 3:53 PM
>>>> On 2021/2/4 14:52, Tian, Kevin wrote:>>> In reality, many
>>>>>>> devices allow I/O faulting only in selective contexts. However, there
>>>>>>> is no standard way (e.g. PCISIG) for the device to report whether
>>>>>>> arbitrary I/O fault is allowed. Then we may have to maintain device
>>>>>>> specific knowledge in software, e.g. in an opt-in table to list devices
>>>>>>> which allows arbitrary faults. For devices which only support selective
>>>>>>> faulting, a mediator (either through vendor extensions on vfio-pci-core
>>>>>>> or a mdev wrapper) might be necessary to help lock down non-
>> faultable
>>>>>>> mappings and then enable faulting on the rest mappings.
>>>>>> For devices which only support selective faulting, they could tell it to the
>>>>>> IOMMU driver and let it filter out non-faultable faults? Do I get it wrong?
>>>>> Not exactly to IOMMU driver. There is already a vfio_pin_pages() for
>>>>> selectively page-pinning. The matter is that 'they' imply some device
>>>>> specific logic to decide which pages must be pinned and such knowledge
>>>>> is outside of VFIO.
>>>>> From enabling p.o.v we could possibly do it in phased approach. First
>>>>> handles devices which tolerate arbitrary DMA faults, and then extends
>>>>> to devices with selective-faulting. The former is simpler, but with one
>>>>> main open whether we want to maintain such device IDs in a static
>>>>> table in VFIO or rely on some hints from other components (e.g. PF
>>>>> driver in VF assignment case). Let's see how Alex thinks about it.
>>>> Hi Kevin,
>>>> You mentioned selective-faulting some time ago. I still have some doubt
>>>> about it:
>>>> There is already a vfio_pin_pages() which is used for limiting the IOMMU
>>>> group dirty scope to pinned pages, could it also be used for indicating
>>>> the faultable scope is limited to the pinned pages and the rest mappings
>>>> is non-faultable that should be pinned and mapped immediately? But it
>>>> seems to be a little weird and not exactly to what you meant... I will
>>>> be grateful if you can help to explain further. :-)
>>> The opposite, i.e. the vendor driver uses vfio_pin_pages to lock down
>>> pages that are not faultable (based on its specific knowledge) and then
>>> the rest memory becomes faultable.
>> Ahh...
>> Thus, from the perspective of VFIO IOMMU, if IOPF enabled for such device,
>> only the page faults within the pinned range are valid in the registered
>> iommu fault handler...
>> I have another question here, for the IOMMU backed devices, they are
>> already
>> all pinned and mapped when attaching, is there a need to call
>> vfio_pin_pages()
>> to lock down pages for them? Did I miss something?...
> If a device is marked as supporting I/O page fault (fully or selectively), 
> there should be no pinning at attach or DMA_MAP time (suppose as 
> this series does). Then for devices with selective-faulting its vendor 
> driver will lock down the pages which are not faultable at run-time, 
> e.g. when intercepting guest registration of a ring buffer...

Get it. Thanks a lot for this! :-)


> Thanks
> Kevin

  reply	other threads:[~2021-03-18 12:48 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-25  9:03 [RFC PATCH v1 0/4] vfio: Add IOPF support for VFIO passthrough Shenming Lu
2021-01-25  9:03 ` [RFC PATCH v1 1/4] vfio/type1: Add a bitmap to track IOPF mapped pages Shenming Lu
2021-01-29 22:58   ` Alex Williamson
2021-01-30  9:31     ` Shenming Lu
2021-01-25  9:04 ` [RFC PATCH v1 2/4] vfio: Add a page fault handler Shenming Lu
2021-01-27 17:42   ` Christoph Hellwig
2021-01-28  6:10     ` Shenming Lu
2021-01-25  9:04 ` [RFC PATCH v1 3/4] vfio: Try to enable IOPF for VFIO devices Shenming Lu
2021-01-29 22:42   ` Alex Williamson
2021-01-30  9:31     ` Shenming Lu
2021-01-25  9:04 ` [RFC PATCH v1 4/4] vfio: Allow to pin and map dynamically Shenming Lu
2021-01-29 22:57 ` [RFC PATCH v1 0/4] vfio: Add IOPF support for VFIO passthrough Alex Williamson
2021-01-30  9:30   ` Shenming Lu
2021-02-01  7:56   ` Tian, Kevin
2021-02-02  6:41     ` Shenming Lu
2021-02-04  6:52       ` Tian, Kevin
2021-02-05 10:37         ` Jean-Philippe Brucker
2021-02-07  8:20           ` Tian, Kevin
2021-02-07 11:47             ` Shenming Lu
2021-02-09 11:06         ` Liu, Yi L
2021-02-10  8:02           ` Shenming Lu
2021-03-18  7:53         ` Shenming Lu
2021-03-18  9:07           ` Tian, Kevin
2021-03-18 11:53             ` Shenming Lu
2021-03-18 12:32               ` Tian, Kevin
2021-03-18 12:47                 ` Shenming Lu [this message]
2021-03-19  0:33               ` Lu Baolu
2021-03-19  1:30                 ` Keqian Zhu
2021-03-20  1:35                   ` Lu Baolu

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