Messages in this thread | | | Subject | Re: [RFC PATCH v1 0/4] vfio: Add IOPF support for VFIO passthrough | From | Lu Baolu <> | Date | Sat, 20 Mar 2021 09:35:55 +0800 |
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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, baolu
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