linux-kernel - [RFC 10/10] mm: thp: x86: cleanup PSE feature bit usage

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Message-ID: <8dc0695aa1c1073ec475be18e300ec1046344e84.1762464515.git.luizcap@redhat.com>
Date: Thu,  6 Nov 2025 16:28:57 -0500
From: Luiz Capitulino <luizcap@...hat.com>
To: david@...nel.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Cc: ryan.roberts@....com,
	akpm@...ux-foundation.org,
	lorenzo.stoakes@...cle.com
Subject: [RFC 10/10] mm: thp: x86: cleanup PSE feature bit usage

Historically, THP support on x86 checked the PSE feature bit to enable
THP. On 64-bit, this check is redundant since PSE is always enabled by
default for compatibility. On 32-bit, PSE enables 4MB page support and
must be checked. To clean this up, this commit:

1. Drops arch_has_pmd_leaves() from common x86 code. For 64-bit,
   we assume PMD-sized pages are always supported

2. Checks for PSE only on 32-bit, using arch_has_pmd_leaves()

Signed-off-by: Luiz Capitulino <luizcap@...hat.com>
---
 arch/x86/include/asm/pgtable.h    | 6 ------
 arch/x86/include/asm/pgtable_32.h | 6 ++++++
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 08d109280e36..55b88de5178f 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -313,12 +313,6 @@ static inline int pud_trans_huge(pud_t pud)
 }
 #endif
 
-#define arch_has_pmd_leaves arch_has_pmd_leaves
-static inline int arch_has_pmd_leaves(void)
-{
-	return boot_cpu_has(X86_FEATURE_PSE);
-}
-
 #ifdef CONFIG_ARCH_SUPPORTS_PMD_PFNMAP
 static inline bool pmd_special(pmd_t pmd)
 {
diff --git a/arch/x86/include/asm/pgtable_32.h b/arch/x86/include/asm/pgtable_32.h
index b612cc57a4d3..3bd51cfa431e 100644
--- a/arch/x86/include/asm/pgtable_32.h
+++ b/arch/x86/include/asm/pgtable_32.h
@@ -45,6 +45,12 @@ do {						\
 	flush_tlb_one_kernel((vaddr));		\
 } while (0)
 
+#define arch_has_pmd_leaves arch_has_pmd_leaves
+static inline int arch_has_pmd_leaves(void)
+{
+	return boot_cpu_has(X86_FEATURE_PSE);
+}
+
 #endif /* !__ASSEMBLER__ */
 
 /*
-- 
2.51.1