Messages in this thread | | | Subject | Re: [RFC PATCH v1 0/4] vfio: Add IOPF support for VFIO passthrough | From | Lu Baolu <> | Date | Fri, 19 Mar 2021 08:33:27 +0800 |
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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.
> 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?...
Best regards, baolu
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