diff options
| author | David Hildenbrand <david@redhat.com> | 2023-08-03 17:32:06 +0300 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2023-08-22 00:28:42 +0300 |
| commit | 14fb1fd751fa09440634b909e6f5f53e2cba9ae0 (patch) | |
| tree | 0388b00259becb274240900774e58bb095af8f39 /include | |
| parent | 7acddcc1ae30670449d60dc9da5b00d544a5b58b (diff) | |
| download | linux-14fb1fd751fa09440634b909e6f5f53e2cba9ae0.tar.xz | |
pgtable: improve pte_protnone() comment
Especially the "For PROT_NONE VMAs, the PTEs are not marked
_PAGE_PROTNONE" part is wrong: doing an mprotect(PROT_NONE) will end up
marking all PTEs on x86_64 as _PAGE_PROTNONE, making pte_protnone()
indicate "yes".
So let's improve the comment, so it's easier to grasp which semantics
pte_protnone() actually has.
Link: https://lkml.kernel.org/r/20230803143208.383663-6-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: liubo <liubo254@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/pgtable.h | 16 |
1 files changed, 10 insertions, 6 deletions
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h index f34e0f2cb4d8..6064f454c8e3 100644 --- a/include/linux/pgtable.h +++ b/include/linux/pgtable.h @@ -1333,12 +1333,16 @@ static inline int pud_trans_unstable(pud_t *pud) #ifndef CONFIG_NUMA_BALANCING /* - * Technically a PTE can be PROTNONE even when not doing NUMA balancing but - * the only case the kernel cares is for NUMA balancing and is only ever set - * when the VMA is accessible. For PROT_NONE VMAs, the PTEs are not marked - * _PAGE_PROTNONE so by default, implement the helper as "always no". It - * is the responsibility of the caller to distinguish between PROT_NONE - * protections and NUMA hinting fault protections. + * In an inaccessible (PROT_NONE) VMA, pte_protnone() may indicate "yes". It is + * perfectly valid to indicate "no" in that case, which is why our default + * implementation defaults to "always no". + * + * In an accessible VMA, however, pte_protnone() reliably indicates PROT_NONE + * page protection due to NUMA hinting. NUMA hinting faults only apply in + * accessible VMAs. + * + * So, to reliably identify PROT_NONE PTEs that require a NUMA hinting fault, + * looking at the VMA accessibility is sufficient. */ static inline int pte_protnone(pte_t pte) { |