From: Baoquan He Date: Thu, 10 Apr 2025 03:57:15 +0000 (+0800) Subject: mm/gup: remove unneeded checking in follow_page_pte() X-Git-Tag: v6.16-rc1~92^2~165 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ede27b7ee2e6c0c5148d4bab04e5d287d6fbc771;p=thirdparty%2Flinux.git mm/gup: remove unneeded checking in follow_page_pte() Patch series "mm/gup: Minor fix, cleanup and improvements", v4. These were made from code inspection in mm/gup.c. This patch (of 3): In __get_user_pages(), it will traverse page table and take a reference to the page the given user address corresponds to if GUP_GET or GUP_PIN is set. However, it's not supported both GUP_GET and GUP_PIN are set. Even though this check need be done, it should be done earlier, but not doing it till entering into follow_page_pte() and failed. Furthermore, this checking has been done in is_valid_gup_args() and all external users of __get_user_pages() will call is_valid_gup_args() to catch the illegal setting. We don't need to worry about internal users of __get_user_pages() because the gup_flags are set by MM code correctly. Here remove the checking in follow_page_pte(), and add VM_WARN_ON_ONCE() to catch the possible exceptional setting just in case. And also change the VM_BUG_ON to VM_WARN_ON_ONCE() for checking (!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN))) because the checking has been done in is_valid_gup_args() for external users of __get_user_pages(). Link: https://lkml.kernel.org/r/20250410035717.473207-1-bhe@redhat.com Link: https://lkml.kernel.org/r/20250410035717.473207-3-bhe@redhat.com Signed-off-by: Baoquan He Reviewed-by: Oscar Salvador Acked-by: David Hildenbrand Cc: Yanjun.Zhu Signed-off-by: Andrew Morton --- diff --git a/mm/gup.c b/mm/gup.c index 84461d384ae2b..eb668da933e17 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -844,11 +844,6 @@ static struct page *follow_page_pte(struct vm_area_struct *vma, pte_t *ptep, pte; int ret; - /* FOLL_GET and FOLL_PIN are mutually exclusive. */ - if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) == - (FOLL_PIN | FOLL_GET))) - return ERR_PTR(-EINVAL); - ptep = pte_offset_map_lock(mm, pmd, address, &ptl); if (!ptep) return no_page_table(vma, flags, address); @@ -1432,7 +1427,11 @@ static long __get_user_pages(struct mm_struct *mm, start = untagged_addr_remote(mm, start); - VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN))); + VM_WARN_ON_ONCE(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN))); + + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + VM_WARN_ON_ONCE((gup_flags & (FOLL_PIN | FOLL_GET)) == + (FOLL_PIN | FOLL_GET)); do { struct page *page;