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    SubjectRe: [PATCH v2 05/18] mm/gup: introduce pin_user_pages*() and FOLL_PIN
    On Mon, Nov 04, 2019 at 03:31:53PM -0500, Jerome Glisse wrote:
    > > Note for Jason: the (a) or (b) items are talking about the vfio case, which is
    > > one of the two call sites that now use pin_longterm_pages_remote(), and the
    > > other one is infiniband:
    > >
    > > drivers/infiniband/core/umem_odp.c:646: npages = pin_longterm_pages_remote(owning_process, owning_mm,
    > > drivers/vfio/vfio_iommu_type1.c:353: ret = pin_longterm_pages_remote(NULL, mm, vaddr, 1,
    >
    > vfio should be reverted until it can be properly implemented.
    > The issue is that when you fix the implementation you might
    > break vfio existing user and thus regress the kernel from user
    > point of view. So i rather have the change to vfio reverted,
    > i believe it was not well understood when it got upstream,
    > between in my 5.4 tree it is still gup_remote not longterm.

    It is clearly a bug, vfio must use LONGTERM, and does right above this
    remote call:

    if (mm == current->mm) {
    ret = get_user_pages(vaddr, 1, flags | FOLL_LONGTERM, page,
    vmas);
    } else {
    ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags, page,
    vmas, NULL);


    I'm not even sure that it really makes any sense to build a 'if' like
    that, surely just always call remote??

    Jason

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