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MADV_DONTNEED historically rejects mlocked ranges, but with MLOCK_ONFAULT and MCL_ONFAULT allowing to mlock without populating, there are valid use cases for depopulating locked ranges as well. Users mlock memory to protect secrets. There are allocators for secure buffers that want in-use memory generally mlocked, but cleared and invalidated memory to give up the physical pages. This could be done with explicit munlock -> mlock calls on free -> alloc of course, but that adds two unnecessary syscalls, heavy mmap_sem write locks, vma splits and re-merges - only to get rid of the backing pages. Users also mlockall(MCL_ONFAULT) to suppress sustained paging, but are okay with on-demand initial population. It seems valid to selectively free some memory during the lifetime of such a process, without having to mess with its overall policy. Why add a separate flag? Isn't this a pretty niche usecase? - MADV_DONTNEED has been bailing on locked vmas forever. It's at least conceivable that someone, somewhere is relying on mlock to protect data from perhaps broader invalidation calls. Changing this behavior now could lead to quiet data corruption. - It also clarifies expectations around MADV_FREE and maybe MADV_REMOVE. It avoids the situation where one quietly behaves different than the others. MADV_FREE_LOCKED can be added later. - The combination of mlock() and madvise() in the first place is probably niche. But where it happens, I'd say that dropping pages from a locked region once they don't contain secrets or won't page anymore is much saner than relying on mlock to protect memory from speculative or errant invalidation calls. It's just that we can't change the default behavior because of the two previous points. Given that, an explicit new flag seems to make the most sense. [hannes@cmpxchg.org: fix mips build] Link: https://lkml.kernel.org/r/20220304171912.305060-1-hannes@cmpxchg.org Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Michal Hocko <mhocko@suse.com> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com> Reviewed-by: Shakeel Butt <shakeelb@google.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Nadav Amit <nadav.amit@gmail.com> Cc: David Hildenbrand <david@redhat.com> Cc: Dr. David Alan Gilbert <dgilbert@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
123 lines
4.6 KiB
C
123 lines
4.6 KiB
C
/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
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/*
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* include/asm-xtensa/mman.h
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*
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* Xtensa Processor memory-manager definitions
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*
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* This file is subject to the terms and conditions of the GNU General Public
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* License. See the file "COPYING" in the main directory of this archive
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* for more details.
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*
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* Copyright (C) 1995 by Ralf Baechle
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* Copyright (C) 2001 - 2005 Tensilica Inc.
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*/
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#ifndef _XTENSA_MMAN_H
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#define _XTENSA_MMAN_H
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/*
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* Protections are chosen from these bits, OR'd together. The
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* implementation does not necessarily support PROT_EXEC or PROT_WRITE
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* without PROT_READ. The only guarantees are that no writing will be
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* allowed without PROT_WRITE and no access will be allowed for PROT_NONE.
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*/
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#define PROT_NONE 0x0 /* page can not be accessed */
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#define PROT_READ 0x1 /* page can be read */
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#define PROT_WRITE 0x2 /* page can be written */
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#define PROT_EXEC 0x4 /* page can be executed */
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#define PROT_SEM 0x10 /* page may be used for atomic ops */
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#define PROT_GROWSDOWN 0x01000000 /* mprotect flag: extend change to start of growsdown vma */
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#define PROT_GROWSUP 0x02000000 /* mprotect flag: extend change to end fo growsup vma */
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/*
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* Flags for mmap
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*/
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/* 0x01 - 0x03 are defined in linux/mman.h */
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#define MAP_TYPE 0x00f /* Mask for type of mapping */
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#define MAP_FIXED 0x010 /* Interpret addr exactly */
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/* not used by linux, but here to make sure we don't clash with ABI defines */
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#define MAP_RENAME 0x020 /* Assign page to file */
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#define MAP_AUTOGROW 0x040 /* File may grow by writing */
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#define MAP_LOCAL 0x080 /* Copy on fork/sproc */
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#define MAP_AUTORSRV 0x100 /* Logical swap reserved on demand */
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/* These are linux-specific */
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#define MAP_NORESERVE 0x0400 /* don't check for reservations */
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#define MAP_ANONYMOUS 0x0800 /* don't use a file */
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#define MAP_GROWSDOWN 0x1000 /* stack-like segment */
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#define MAP_DENYWRITE 0x2000 /* ETXTBSY */
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#define MAP_EXECUTABLE 0x4000 /* mark it as an executable */
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#define MAP_LOCKED 0x8000 /* pages are locked */
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#define MAP_POPULATE 0x10000 /* populate (prefault) pagetables */
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#define MAP_NONBLOCK 0x20000 /* do not block on IO */
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#define MAP_STACK 0x40000 /* give out an address that is best suited for process/thread stacks */
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#define MAP_HUGETLB 0x80000 /* create a huge page mapping */
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#define MAP_FIXED_NOREPLACE 0x100000 /* MAP_FIXED which doesn't unmap underlying mapping */
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#define MAP_UNINITIALIZED 0x4000000 /* For anonymous mmap, memory could be
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* uninitialized */
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/*
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* Flags for msync
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*/
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#define MS_ASYNC 0x0001 /* sync memory asynchronously */
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#define MS_INVALIDATE 0x0002 /* invalidate mappings & caches */
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#define MS_SYNC 0x0004 /* synchronous memory sync */
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/*
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* Flags for mlockall
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*/
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#define MCL_CURRENT 1 /* lock all current mappings */
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#define MCL_FUTURE 2 /* lock all future mappings */
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#define MCL_ONFAULT 4 /* lock all pages that are faulted in */
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/*
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* Flags for mlock
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*/
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#define MLOCK_ONFAULT 0x01 /* Lock pages in range after they are faulted in, do not prefault */
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#define MADV_NORMAL 0 /* no further special treatment */
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#define MADV_RANDOM 1 /* expect random page references */
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#define MADV_SEQUENTIAL 2 /* expect sequential page references */
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#define MADV_WILLNEED 3 /* will need these pages */
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#define MADV_DONTNEED 4 /* don't need these pages */
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/* common parameters: try to keep these consistent across architectures */
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#define MADV_FREE 8 /* free pages only if memory pressure */
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#define MADV_REMOVE 9 /* remove these pages & resources */
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#define MADV_DONTFORK 10 /* don't inherit across fork */
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#define MADV_DOFORK 11 /* do inherit across fork */
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#define MADV_MERGEABLE 12 /* KSM may merge identical pages */
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#define MADV_UNMERGEABLE 13 /* KSM may not merge identical pages */
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#define MADV_HUGEPAGE 14 /* Worth backing with hugepages */
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#define MADV_NOHUGEPAGE 15 /* Not worth backing with hugepages */
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#define MADV_DONTDUMP 16 /* Explicity exclude from the core dump,
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overrides the coredump filter bits */
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#define MADV_DODUMP 17 /* Clear the MADV_NODUMP flag */
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#define MADV_WIPEONFORK 18 /* Zero memory on fork, child only */
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#define MADV_KEEPONFORK 19 /* Undo MADV_WIPEONFORK */
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#define MADV_COLD 20 /* deactivate these pages */
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#define MADV_PAGEOUT 21 /* reclaim these pages */
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#define MADV_POPULATE_READ 22 /* populate (prefault) page tables readable */
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#define MADV_POPULATE_WRITE 23 /* populate (prefault) page tables writable */
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#define MADV_DONTNEED_LOCKED 24 /* like DONTNEED, but drop locked pages too */
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/* compatibility flags */
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#define MAP_FILE 0
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#define PKEY_DISABLE_ACCESS 0x1
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#define PKEY_DISABLE_WRITE 0x2
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#define PKEY_ACCESS_MASK (PKEY_DISABLE_ACCESS |\
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PKEY_DISABLE_WRITE)
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#endif /* _XTENSA_MMAN_H */
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