lkml.org 
[lkml]   [2021]   [Mar]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [RFC PATCH v1 0/4] vfio: Add IOPF support for VFIO passthrough
    From
    Date
    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

    \
     
     \ /
      Last update: 2021-03-19 01:44    [W:3.027 / U:0.208 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site