On Mon, Sep 21, 2026 at 12:00:43PM +0100, Vincent Donnefort wrote:
Keeping PTE-level mappings is interesting on some architectures as it allows mapping/unmapping pages from the kernel direct map without the risk of splitting blocks which, under the break-before-make rule, may trigger page-faults the kernel can't handle.
Let's be honest, it's arm64 :)
I believe that some powerpc variants could use this too, but they don't have break-before-make, so either "some architectures" or "break-before-make" should be rephrased.
However, mapping the entire direct map at PTE-level is costly. So instead, create a new memblock flag MEMBLOCK_PTEMAP to selectively apply a PTE-level mapping.
Signed-off-by: Vincent Donnefort vdonnefort@google.com
include/linux/memblock.h | 18 ++++++++++++++++++ mm/memblock.c | 30 ++++++++++++++++++++++++++++++ 2 files changed, 48 insertions(+)
diff --git a/include/linux/memblock.h b/include/linux/memblock.h index aa845f488327..13263055996d 100644 --- a/include/linux/memblock.h +++ b/include/linux/memblock.h
...
@@ -285,8 +289,16 @@ static inline bool memblock_is_mirror(struct memblock_region *m) return m->flags & MEMBLOCK_MIRROR; } +static inline void memblock_warn_invalid_map_flags(struct memblock_region *m) +{
- enum memblock_flags map_flags = MEMBLOCK_NOMAP | MEMBLOCK_PTEMAP;
- WARN_ON_ONCE((m->flags & map_flags) == map_flags);
+}
static inline bool memblock_is_nomap(struct memblock_region *m) {
- memblock_warn_invalid_map_flags(m);
I think it's better to check and warn when setting an incompatible flag rather than when querying it.
return m->flags & MEMBLOCK_NOMAP; }