From 54d020692b342f7bd02d7f5795fb5c401caecfcc Mon Sep 17 00:00:00 2001 From: Lorenzo Stoakes Date: Wed, 17 May 2023 20:25:33 +0100 Subject: mm/gup: remove unused vmas parameter from get_user_pages() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Patch series "remove the vmas parameter from GUP APIs", v6. (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 can only be accessed with the mmap_lock held 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 case 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, abstracted to a new get_user_page_vma_remote() inline helper function which also performs error checking and reference count maintenance. The special case is io_uring, where io_pin_pages() specifically needs to assert that the VMAs underlying the range do not result in broken long-term GUP file-backed mappings. As GUP now internally asserts that FOLL_LONGTERM mappings are not file-backed in a broken fashion (i.e. requiring dirty tracking) - as implemented in "mm/gup: disallow FOLL_LONGTERM GUP-nonfast writing to file-backed mappings" - this logic is no longer required and so we can simply remove it altogether from io_uring. Eliminating the vmas parameter eliminates an entire class of danging pointer errors that might have occured should the lock have been incorrectly released. In addition, the API is simplified and now clearly expresses what it is intended 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. I have run this series against gup_test with no issues. Thanks to Matthew Wilcox for suggesting this refactoring! This patch (of 6): No invocation of get_user_pages() use the vmas parameter, so remove it. The GUP API is confusing and caveated. Recent changes have done much to improve that, however there is more we can do. Exporting vmas is a prime target as the caller has to be extremely careful to preclude their use after the mmap_lock has expired or otherwise be left with dangling pointers. Removing the vmas parameter focuses the GUP functions upon their primary purpose - pinning (and outputting) pages as well as performing the actions implied by the input flags. This is part of a patch series aiming to remove the vmas parameter altogether. Link: https://lkml.kernel.org/r/cover.1684350871.git.lstoakes@gmail.com Link: https://lkml.kernel.org/r/589e0c64794668ffc799651e8d85e703262b1e9d.1684350871.git.lstoakes@gmail.com Signed-off-by: Lorenzo Stoakes Suggested-by: Matthew Wilcox (Oracle) Acked-by: Greg Kroah-Hartman Acked-by: David Hildenbrand Reviewed-by: Jason Gunthorpe Acked-by: Christian König (for radeon parts) Acked-by: Jarkko Sakkinen Reviewed-by: Christoph Hellwig Acked-by: Sean Christopherson (KVM) Cc: Catalin Marinas Cc: Dennis Dalessandro Cc: Janosch Frank Cc: Jens Axboe Cc: Sakari Ailus Signed-off-by: Andrew Morton --- virt/kvm/kvm_main.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'virt') diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 479802a892d4..51e4882d0873 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -2477,7 +2477,7 @@ static inline int check_user_page_hwpoison(unsigned long addr) { int rc, flags = FOLL_HWPOISON | FOLL_WRITE; - rc = get_user_pages(addr, 1, flags, NULL, NULL); + rc = get_user_pages(addr, 1, flags, NULL); return rc == -EHWPOISON; } -- cgit v1.2.3-70-g09d2