Commit 55b8fe70 authored Aug 17, 2021 by Andreas Gruenbacher

gup: Introduce FOLL_NOFAULT flag to disable page faults



Introduce a new FOLL_NOFAULT flag that causes get_user_pages to return
-EFAULT when it would otherwise trigger a page fault.  This is roughly
similar to FOLL_FAST_ONLY but available on all architectures, and less
fragile.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

parent 4fdccaa0

include/linux/mm.h

+2 −1

Original line number	Diff line number	Diff line
		@@ -2851,7 +2851,8 @@ struct page follow_page(struct vm_area_struct vma, unsigned long address,
		#define FOLL_FORCE 0x10 /* get_user_pages read/write w/o permission */
		#define FOLL_NOWAIT 0x20 /* if a disk transfer is needed, start the IO
		* and return without waiting upon it */
		#define FOLL_POPULATE 0x40 /* fault in page */
		#define FOLL_POPULATE 0x40 /* fault in pages (with FOLL_MLOCK) */
		#define FOLL_NOFAULT 0x80 /* do not fault in pages */
		#define FOLL_HWPOISON 0x100 /* check page is hwpoisoned */
		#define FOLL_NUMA 0x200 /* force NUMA hinting page fault */
		#define FOLL_MIGRATION 0x400 /* wait for page to replace migration entry */

mm/gup.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -918,6 +918,8 @@ static int faultin_page(struct vm_area_struct *vma,
		/* mlock all present pages, but do not fault in new pages */
		if ((*flags & (FOLL_POPULATE \| FOLL_MLOCK)) == FOLL_MLOCK)
		return -ENOENT;
		if (*flags & FOLL_NOFAULT)
		return -EFAULT;
		if (*flags & FOLL_WRITE)
		fault_flags \|= FAULT_FLAG_WRITE;
		if (*flags & FOLL_REMOTE)
		@@ -2843,7 +2845,7 @@ static int internal_get_user_pages_fast(unsigned long start,

		if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE \| FOLL_LONGTERM \|
		FOLL_FORCE \| FOLL_PIN \| FOLL_GET \|
		FOLL_FAST_ONLY)))
		FOLL_FAST_ONLY \| FOLL_NOFAULT)))
		return -EINVAL;

		if (gup_flags & FOLL_PIN)