mm/vmalloc: Gracefully unmap huge ptes

Commit f7ee1f13d606 ("mm/vmalloc: enable mapping of huge pages at pte
level in vmap") added its support by reusing the set_huge_pte_at() API,
which is otherwise only used for user mappings. But when unmapping those
huge ptes, it continued to call ptep_get_and_clear(), which is a
layering violation. To date, the only arch to implement this support is
powerpc and it all happens to work ok for it.

But arm64's implementation of ptep_get_and_clear() can not be safely
used to clear a previous set_huge_pte_at(). So let's introduce a new
arch opt-in function, arch_vmap_pte_range_unmap_size(), which can
provide the size of a (present) pte. Then we can call
huge_ptep_get_and_clear() to tear it down properly.

Note that if vunmap_range() is called with a range that starts in the
middle of a huge pte-mapped page, we must unmap the entire huge page so
the behaviour is consistent with pmd and pud block mappings. In this
case emit a warning just like we do for pmd/pud mappings.

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Tested-by: Luiz Capitulino <luizcap@redhat.com>
Link: https://lore.kernel.org/r/20250422081822.1836315-9-ryan.roberts@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

2 files changed, 24 insertions, 2 deletions

diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 31e9ffd936e3..16dd4cba64f2 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -113,6 +113,14 @@ static inline unsigned long arch_vmap_pte_range_map_size(unsigned long addr, uns
 }
 #endif
 
+#ifndef arch_vmap_pte_range_unmap_size
+static inline unsigned long arch_vmap_pte_range_unmap_size(unsigned long addr,
+							   pte_t *ptep)
+{
+	return PAGE_SIZE;
+}
+#endif
+
 #ifndef arch_vmap_pte_supported_shift
 static inline int arch_vmap_pte_supported_shift(unsigned long size)
 {
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index d60d3a29d149..fe2e2cc8da94 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -350,12 +350,26 @@ static void vunmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 			     pgtbl_mod_mask *mask)
 {
 	pte_t *pte;
+	pte_t ptent;
+	unsigned long size = PAGE_SIZE;
 
 	pte = pte_offset_kernel(pmd, addr);
 	do {
-		pte_t ptent = ptep_get_and_clear(&init_mm, addr, pte);
+#ifdef CONFIG_HUGETLB_PAGE
+		size = arch_vmap_pte_range_unmap_size(addr, pte);
+		if (size != PAGE_SIZE) {
+			if (WARN_ON(!IS_ALIGNED(addr, size))) {
+				addr = ALIGN_DOWN(addr, size);
+				pte = PTR_ALIGN_DOWN(pte, sizeof(*pte) * (size >> PAGE_SHIFT));
+			}
+			ptent = huge_ptep_get_and_clear(&init_mm, addr, pte, size);
+			if (WARN_ON(end - addr < size))
+				size = end - addr;
+		} else
+#endif
+			ptent = ptep_get_and_clear(&init_mm, addr, pte);
 		WARN_ON(!pte_none(ptent) && !pte_present(ptent));
-	} while (pte++, addr += PAGE_SIZE, addr != end);
+	} while (pte += (size >> PAGE_SHIFT), addr += size, addr != end);
 	*mask |= PGTBL_PTE_MODIFIED;
 }