(pin_/get)_user_pages[_remote]() each provide an optional output parameter for an array of VMA objects associated with each page in the input range. These provide the means for VMAs to be returned, as long as mm->mmap_lock is never released during the GUP operation (i.e. the internal flag FOLL_UNLOCKABLE is not specified). In addition, these VMAs have also to only be accessed under the mmap_lock, and become invalidated the moment it is released. The vast majority of invocations do not use this functionality and of those that do, all but one retrieve a single VMA to perform checks upon. It is not egregious in the single VMA cases to simply replace the operation with a vma_lookup(). In these cases we duplicate the (fast) lookup on a slow path already under the mmap_lock. The special case is io_uring, where io_pin_pages() specifically needs to assert that all the VMAs possess the same vm->vm_file (possibly NULL) and they are either anonymous or hugetlb pages. To continue to provide this functionality, we introduce the FOLL_SAME_PAGE flag which asserts that the vma->vm_file remains the same throughout, erroring out if this is not the case. We can then replace the io_uring case by passing FOLL_SAME_FILE and looking up the first VMA manually and performing the required checks on this alone. The combination of the two amount to the same checks being performed (and avoids an allocation). Eliminating this parameter eliminates an entire class of errors - the vmas array used to become a set of dangling pointers if access after release of mmap_lock was attempted, this is simply no longer possible. In addition the API is simplified and now clearly expresses what it is for - applying the specified GUP flags and (if pinning) returning pinned pages. This change additionally opens the door to further potential improvements in GUP and the possible marrying of disparate code paths. Thanks to Matthew Wilcox for suggesting this refactoring! Lorenzo Stoakes (7): mm/gup: remove unused vmas parameter from get_user_pages() mm/gup: remove unused vmas parameter from pin_user_pages_remote() mm/gup: remove vmas parameter from get_user_pages_remote() mm/gup: introduce the FOLL_SAME_FILE GUP flag io_uring: rsrc: use FOLL_SAME_FILE on pin_user_pages() mm/gup: remove vmas parameter from pin_user_pages() mm/gup: remove vmas array from internal GUP functions arch/arm64/kernel/mte.c | 5 +- arch/powerpc/mm/book3s64/iommu_api.c | 2 +- arch/s390/kvm/interrupt.c | 2 +- arch/x86/kernel/cpu/sgx/ioctl.c | 2 +- drivers/gpu/drm/radeon/radeon_ttm.c | 2 +- drivers/infiniband/hw/qib/qib_user_pages.c | 2 +- drivers/infiniband/hw/usnic/usnic_uiom.c | 2 +- drivers/infiniband/sw/siw/siw_mem.c | 2 +- drivers/iommu/iommufd/pages.c | 4 +- drivers/media/v4l2-core/videobuf-dma-sg.c | 2 +- drivers/misc/sgi-gru/grufault.c | 2 +- drivers/vdpa/vdpa_user/vduse_dev.c | 2 +- drivers/vfio/vfio_iommu_type1.c | 2 +- drivers/vhost/vdpa.c | 2 +- fs/exec.c | 2 +- include/linux/hugetlb.h | 10 +- include/linux/mm.h | 10 +- include/linux/mm_types.h | 2 + io_uring/rsrc.c | 39 +++---- kernel/events/uprobes.c | 10 +- mm/gup.c | 121 ++++++++------------- mm/gup_test.c | 14 +-- mm/hugetlb.c | 24 ++-- mm/memory.c | 9 +- mm/process_vm_access.c | 2 +- mm/rmap.c | 2 +- net/xdp/xdp_umem.c | 2 +- security/tomoyo/domain.c | 2 +- virt/kvm/async_pf.c | 3 +- virt/kvm/kvm_main.c | 4 +- 30 files changed, 125 insertions(+), 164 deletions(-) -- 2.40.0
