diff options
| author | David Hildenbrand <david@redhat.com> | 2023-01-02 17:08:54 +0100 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2023-01-18 17:12:56 -0800 |
| commit | fc4f4be9b5271e43eeb4c675d190fa9734de9ea3 (patch) | |
| tree | fbdc88b711df8a850345a8539784b29e84d7c920 /include/linux/mm.h | |
| parent | da0618c146ca0e1412173a8a229dd737a73b1a4f (diff) | |
| download | linux-fc4f4be9b5271e43eeb4c675d190fa9734de9ea3.tar.gz | |
mm/nommu: factor out check for NOMMU shared mappings into is_nommu_shared_mapping()
Patch series "mm/nommu: don't use VM_MAYSHARE for MAP_PRIVATE mappings".
Trying to reduce the confusion around VM_SHARED and VM_MAYSHARE first
requires !CONFIG_MMU to stop using VM_MAYSHARE for MAP_PRIVATE mappings.
CONFIG_MMU only sets VM_MAYSHARE for MAP_SHARED mappings.
This paves the way for further VM_MAYSHARE and VM_SHARED cleanups: for
example, renaming VM_MAYSHARED to VM_MAP_SHARED to make it cleaner what is
actually means.
Let's first get the weird case out of the way and not use VM_MAYSHARE in
MAP_PRIVATE mappings, using a new VM_MAYOVERLAY flag instead.
This patch (of 3):
We want to stop using VM_MAYSHARE in private mappings to pave the way for
clarifying the semantics of VM_MAYSHARE vs. VM_SHARED and reduce the
confusion. While CONFIG_MMU uses VM_MAYSHARE to represent MAP_SHARED,
!CONFIG_MMU also sets VM_MAYSHARE for selected R/O private file mappings
that are an effective overlay of a file mapping.
Let's factor out all relevant VM_MAYSHARE checks in !CONFIG_MMU code into
is_nommu_shared_mapping() first.
Note that whenever VM_SHARED is set, VM_MAYSHARE must be set as well
(unless there is a serious BUG). So there is not need to test for
VM_SHARED manually.
No functional change intended.
Link: https://lkml.kernel.org/r/20230102160856.500584-1-david@redhat.com
Link: https://lkml.kernel.org/r/20230102160856.500584-2-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: David Hildenbrand <david@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Nicolas Pitre <nico@fluxnic.net>
Cc: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'include/linux/mm.h')
| -rw-r--r-- | include/linux/mm.h | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h index eb5bfc77c2c28..791bac40bf8ed 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1347,6 +1347,21 @@ static inline bool is_cow_mapping(vm_flags_t flags) return (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE; } +#ifndef CONFIG_MMU +static inline bool is_nommu_shared_mapping(vm_flags_t flags) +{ + /* + * NOMMU shared mappings are ordinary MAP_SHARED mappings and selected + * R/O MAP_PRIVATE file mappings that are an effective R/O overlay of + * a file mapping. R/O MAP_PRIVATE mappings might still modify + * underlying memory if ptrace is active, so this is only possible if + * ptrace does not apply. Note that there is no mprotect() to upgrade + * write permissions later. + */ + return flags & VM_MAYSHARE; +} +#endif + #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP) #define SECTION_IN_PAGE_FLAGS #endif |