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From: Lu Baolu <baolu.lu@linux.intel.com>
To: Keqian Zhu <zhukeqian1@huawei.com>,
	Shenming Lu <lushenming@huawei.com>,
	"Tian, Kevin" <kevin.tian@intel.com>,
	Alex Williamson <alex.williamson@redhat.com>
Cc: baolu.lu@linux.intel.com, 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>,
	"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: Sat, 20 Mar 2021 09:35:55 +0800	[thread overview]
Message-ID: <993b34b0-a68e-87eb-854d-ce926db8702b@linux.intel.com> (raw)
In-Reply-To: <4327b3ac-858d-30d0-9fe4-bd4ccc0fbd40@huawei.com>

On 3/19/21 9:30 AM, Keqian Zhu wrote:
> Hi Baolu,
> On 2021/3/19 8:33, Lu Baolu wrote:
>> On 3/18/21 7:53 PM, Shenming Lu wrote:
>>> 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...
>> Isn't it opposite? The pinned pages will never generate any page faults.
>> I might miss some contexts here.
> It seems that vfio_pin_pages() just pin some pages and record the pinned scope to pfn_list of vfio_dma.
> No mapping is established, so we still has page faults.

Make sense. Thanks a lot for the explanation.

> IIUC, vfio_pin_pages() is used to
> 1. pin pages for non-iommu backed devices.
> 2. mark dirty scope for non-iommu backed devices and iommu backed devices.

Best regards,

      reply	other threads:[~2021-03-20  1:46 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
2021-03-19  0:33               ` Lu Baolu
2021-03-19  1:30                 ` Keqian Zhu
2021-03-20  1:35                   ` Lu Baolu [this message]

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