[PATCH 1/2] riscv: Recognize P4D leaves when splitting the linear mapping

[Jackie Liu]

From: Jackie Liu <liuyun01 at kylinos.cn>

The linear mapping can contain P4D leaves on Sv57, but p4d_leaf() uses
the generic definition which always returns false. Splitting a partial
P4D range therefore treats the mapped physical memory as a PUD table
instead of allocating and populating that table.

Check the hardware leaf bits in the linear-map splitter. Only do so
when the PUD level is present: on Sv39 the folded P4D entry may contain
a PUD leaf, which must be handled by the PUD splitter.

Keep this check local to kernel mappings. Defining p4d_leaf() globally
would conflict with the GUP assertions that userspace P4D leaves are
unsupported.

Link: https://lore.kernel.org/all/sashiko-outbox-190189@kernel.org/
Fixes: 311cd2f6e253 ("riscv: Fix set_memory_XX() and set_direct_map_XX() by splitting huge linear mappings")
Signed-off-by: Jackie Liu <liuyun01 at kylinos.cn>
---
 arch/riscv/mm/pageattr.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/mm/pageattr.c b/arch/riscv/mm/pageattr.c
index 5b3cf326455db..32834a09a8097 100644
--- a/arch/riscv/mm/pageattr.c
+++ b/arch/riscv/mm/pageattr.c
@@ -197,7 +197,8 @@ static int __split_linear_mapping_p4d(pgd_t *pgdp,
 		    vaddr <= (vaddr & P4D_MASK) && end >= next)
 			continue;
 
-		if (p4d_leaf(p4dp_get(p4dp))) {
+		/* p4d_leaf() does not cover kernel-only leaf mappings. */
+		if (pgtable_l4_enabled && (p4d_val(p4dp_get(p4dp)) & _PAGE_LEAF)) {
 			struct page *pud_page;
 			unsigned long pfn = _p4d_pfn(p4dp_get(p4dp));
 			pgprot_t prot = __pgprot(p4d_val(p4dp_get(p4dp)) & ~_PAGE_PFN_MASK);
-- 
2.43.0