linux-kernel - [PATCH v5 6/7] x86/boot: Drop 5-level paging related global variable

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Message-ID: <20250520104138.2734372-15-ardb+git@google.com>
Date: Tue, 20 May 2025 12:41:45 +0200
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: x86@...nel.org, Ard Biesheuvel <ardb@...nel.org>, Ingo Molnar <mingo@...nel.org>, 
	Linus Torvalds <torvalds@...ux-foundation.org>, Brian Gerst <brgerst@...il.com>, 
	"Kirill A. Shutemov" <kirill@...temov.name>, Borislav Petkov <bp@...en8.de>
Subject: [PATCH v5 6/7] x86/boot: Drop 5-level paging related global variable

From: Ard Biesheuvel <ardb@...nel.org>

The variable __pgtable_l5_enabled is no longer used so it can be
dropped.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/boot/compressed/misc.h         |  1 -
 arch/x86/boot/compressed/pgtable_64.c   |  6 ------
 arch/x86/boot/startup/map_kernel.c      | 16 +---------------
 arch/x86/include/asm/pgtable_64_types.h |  2 --
 arch/x86/kernel/head64.c                |  2 --
 5 files changed, 1 insertion(+), 26 deletions(-)

diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index 7f79c426f542..d6860b50afaf 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -190,7 +190,6 @@ static inline int count_immovable_mem_regions(void) { return 0; }
 #endif
 
 /* ident_map_64.c */
-extern unsigned int __pgtable_l5_enabled;
 extern void kernel_add_identity_map(unsigned long start, unsigned long end);
 
 /* Used by PAGE_KERN* macros: */
diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
index 965fca150e68..4772919411a9 100644
--- a/arch/x86/boot/compressed/pgtable_64.c
+++ b/arch/x86/boot/compressed/pgtable_64.c
@@ -10,9 +10,6 @@
 #define BIOS_START_MIN		0x20000U	/* 128K, less than this is insane */
 #define BIOS_START_MAX		0x9f000U	/* 640K, absolute maximum */
 
-/* __pgtable_l5_enabled needs to be in .data to avoid being cleared along with .bss */
-unsigned int __section(".data") __pgtable_l5_enabled;
-
 /* Buffer to preserve trampoline memory */
 static char trampoline_save[TRAMPOLINE_32BIT_SIZE];
 
@@ -118,9 +115,6 @@ asmlinkage void configure_5level_paging(struct boot_params *bp, void *pgtable)
 	if (!cmdline_find_option_bool("no5lvl") &&
 	    native_cpuid_eax(0) >= 7 && (native_cpuid_ecx(7) & BIT(16))) {
 		l5_required = true;
-
-		/* Initialize variables for 5-level paging */
-		__pgtable_l5_enabled = 1;
 	}
 
 	/*
diff --git a/arch/x86/boot/startup/map_kernel.c b/arch/x86/boot/startup/map_kernel.c
index 5d3c6108f1c3..328a343bc355 100644
--- a/arch/x86/boot/startup/map_kernel.c
+++ b/arch/x86/boot/startup/map_kernel.c
@@ -14,20 +14,6 @@
 extern pmd_t early_dynamic_pgts[EARLY_DYNAMIC_PAGE_TABLES][PTRS_PER_PMD];
 extern unsigned int next_early_pgt;
 
-static inline bool check_la57_support(void)
-{
-	/*
-	 * 5-level paging is detected and enabled at kernel decompression
-	 * stage. Only check if it has been enabled there.
-	 */
-	if (!(native_read_cr4() & X86_CR4_LA57))
-		return false;
-
-	__pgtable_l5_enabled	= 1;
-
-	return true;
-}
-
 static unsigned long __head sme_postprocess_startup(struct boot_params *bp,
 						    pmdval_t *pmd,
 						    unsigned long p2v_offset)
@@ -97,7 +83,7 @@ unsigned long __head __startup_64(unsigned long p2v_offset,
 	bool la57;
 	int i;
 
-	la57 = check_la57_support();
+	la57 = pgtable_l5_enabled();
 
 	/* Is the address too large? */
 	if (physaddr >> MAX_PHYSMEM_BITS)
diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
index ed847a90cf4f..3c56b98b87b0 100644
--- a/arch/x86/include/asm/pgtable_64_types.h
+++ b/arch/x86/include/asm/pgtable_64_types.h
@@ -22,8 +22,6 @@ typedef unsigned long	pgprotval_t;
 typedef struct { pteval_t pte; } pte_t;
 typedef struct { pmdval_t pmd; } pmd_t;
 
-extern unsigned int __pgtable_l5_enabled;
-
 #ifndef pgdir_shift
 DECLARE_PER_CPU_CACHE_HOT(u8, __pgdir_shift);
 
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 5e5da6574a83..137c93498601 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -48,8 +48,6 @@ unsigned int __initdata next_early_pgt;
 SYM_PIC_ALIAS(next_early_pgt);
 pmdval_t early_pmd_flags = __PAGE_KERNEL_LARGE & ~(_PAGE_GLOBAL | _PAGE_NX);
 
-unsigned int __pgtable_l5_enabled __ro_after_init;
-
 unsigned long page_offset_base __ro_after_init = __PAGE_OFFSET_BASE_L4;
 EXPORT_SYMBOL(page_offset_base);
 unsigned long vmalloc_base __ro_after_init = __VMALLOC_BASE_L4;
-- 
2.49.0.1101.gccaa498523-goog