> From: Shenming Lu <lushenming@xxxxxxxxxx> > 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. Thanks Kevin
