[PATCH v2 3/5] loongarch/mm: disable device DAX vmemmap optimization

[Muchun Song]

LoongArch selects ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP but not
ARCH_WANT_OPTIMIZE_DAX_VMEMMAP. Its vmemmap_free() implementation is also
empty, so it cannot tear down optimized Device DAX mappings.

A later change removes the generic Device DAX architecture gate and lets
vmemmap_populate() decide whether a section can use optimization. Clear the
section compound order in the LoongArch path so Device DAX keeps using
unoptimized mappings.

This does not affect HugeTLB HVO: LoongArch does not support gigantic
pages, so HugeTLB does not use section-based vmemmap optimization there.

Signed-off-by: Muchun Song <songmuchun at bytedance.com>
---
v2:
- New patch using section_vmemmap_optimization_disable() to keep Device
  DAX vmemmap optimization disabled on LoongArch (reported by Sashiko)
---
 arch/loongarch/mm/init.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/loongarch/mm/init.c b/arch/loongarch/mm/init.c
index f801f7097f03..ea769e479241 100644
--- a/arch/loongarch/mm/init.c
+++ b/arch/loongarch/mm/init.c
@@ -15,6 +15,7 @@
 #include <linux/memblock.h>
 #include <linux/memremap.h>
 #include <linux/mm.h>
+#include <linux/vmemmap-optimization.h>
 #include <linux/mman.h>
 #include <linux/highmem.h>
 #include <linux/swap.h>
@@ -143,6 +144,7 @@ void __meminit vmemmap_set_pmd(pmd_t *pmd, void *p, int node,
 int __meminit vmemmap_populate(unsigned long start, unsigned long end,
 			       int node, struct vmem_altmap *altmap)
 {
+	section_vmemmap_optimization_disable(start, end);
 #if CONFIG_PGTABLE_LEVELS == 2
 	return vmemmap_populate_basepages(start, end, node, NULL);
 #else
-- 
2.54.0