linux-kernel - [PATCH v2 3/3] arm64: mm: Tidy up force_pte

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Message-ID: <20251106160945.3182799-4-ryan.roberts@arm.com>
Date: Thu,  6 Nov 2025 16:09:43 +0000
From: Ryan Roberts <ryan.roberts@....com>
To: catalin.marinas@....com,
	will@...nel.org,
	yang@...amperecomputing.com,
	david@...hat.com,
	ardb@...nel.org,
	dev.jain@....com,
	scott@...amperecomputing.com,
	cl@...two.org
Cc: Ryan Roberts <ryan.roberts@....com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	David Hildenbrand <david@...nel.org>
Subject: [PATCH v2 3/3] arm64: mm: Tidy up force_pte_mapping()

Tidy up the implementation of force_pte_mapping() to make it easier to
read and introduce the split_leaf_mapping_possible() helper to reduce
code duplication in split_kernel_leaf_mapping() and
arch_kfence_init_pool().

Suggested-by: David Hildenbrand (Red Hat) <david@...nel.org>
Signed-off-by: Ryan Roberts <ryan.roberts@....com>
---
 arch/arm64/mm/mmu.c | 43 +++++++++++++++++++++++--------------------
 1 file changed, 23 insertions(+), 20 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 652bb8c14035..2ba01dc8ef82 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -710,12 +710,26 @@ static int split_kernel_leaf_mapping_locked(unsigned long addr)
 
 static inline bool force_pte_mapping(void)
 {
-	bool bbml2 = system_capabilities_finalized() ?
+	const bool bbml2 = system_capabilities_finalized() ?
 		system_supports_bbml2_noabort() : cpu_supports_bbml2_noabort();
 
-	return (!bbml2 && (rodata_full || arm64_kfence_can_set_direct_map() ||
-			   is_realm_world())) ||
-		debug_pagealloc_enabled();
+	if (debug_pagealloc_enabled())
+		return true;
+	if (bbml2)
+		return false;
+	return rodata_full || arm64_kfence_can_set_direct_map() || is_realm_world();
+}
+
+static inline bool split_leaf_mapping_possible(void)
+{
+	/*
+	 * !BBML2_NOABORT systems should never run into scenarios where we would
+	 * have to split. So exit early and let calling code detect it and raise
+	 * a warning.
+	 */
+	if (!system_supports_bbml2_noabort())
+		return false;
+	return !force_pte_mapping();
 }
 
 static DEFINE_MUTEX(pgtable_split_lock);
@@ -725,22 +739,11 @@ int split_kernel_leaf_mapping(unsigned long start, unsigned long end)
 	int ret;
 
 	/*
-	 * !BBML2_NOABORT systems should not be trying to change permissions on
-	 * anything that is not pte-mapped in the first place. Just return early
-	 * and let the permission change code raise a warning if not already
-	 * pte-mapped.
-	 */
-	if (!system_supports_bbml2_noabort())
-		return 0;
-
-	/*
-	 * If the region is within a pte-mapped area, there is no need to try to
-	 * split. Additionally, CONFIG_DEBUG_PAGEALLOC and CONFIG_KFENCE may
-	 * change permissions from atomic context so for those cases (which are
-	 * always pte-mapped), we must not go any further because taking the
-	 * mutex below may sleep.
+	 * Exit early if the region is within a pte-mapped area or if we can't
+	 * split. For the latter case, the permission change code will raise a
+	 * warning if not already pte-mapped.
 	 */
-	if (force_pte_mapping() || is_kfence_address((void *)start))
+	if (!split_leaf_mapping_possible() || is_kfence_address((void *)start))
 		return 0;
 
 	/*
@@ -1039,7 +1042,7 @@ bool arch_kfence_init_pool(void)
 	int ret;
 
 	/* Exit early if we know the linear map is already pte-mapped. */
-	if (!system_supports_bbml2_noabort() || force_pte_mapping())
+	if (!split_leaf_mapping_possible())
 		return true;
 
 	/* Kfence pool is already pte-mapped for the early init case. */
-- 
2.43.0