[RFC PATCH v2 6/6] x86/boot: Drop 5-level paging related variables and early updates

[Ard Biesheuvel <ardb+git@google.com>]

From: Ard Biesheuvel <ardb@kernel.org>

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

Along with it, drop ptrs_per_p4d and pgdir_shift, and replace any
references to those with expressions based on pgtable_l5_enabled(). This
ensures that all observers see values that are mutually consistent.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/x86/boot/compressed/misc.h         |  1 -
 arch/x86/boot/compressed/pgtable_64.c   | 12 -----------
 arch/x86/boot/startup/map_kernel.c      | 21 +-------------------
 arch/x86/include/asm/pgtable_64_types.h |  9 ++-------
 arch/x86/kernel/head64.c                |  8 --------
 5 files changed, 3 insertions(+), 48 deletions(-)

diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index 72b830b8a69c..3d5c6322def8 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, pgdir_shift, ptrs_per_p4d;
 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 5a6c7a190e5b..591d28f2feb6 100644
--- a/arch/x86/boot/compressed/pgtable_64.c
+++ b/arch/x86/boot/compressed/pgtable_64.c
@@ -10,13 +10,6 @@
 #define BIOS_START_MIN		0x20000U	/* 128K, less than this is insane */
 #define BIOS_START_MAX		0x9f000U	/* 640K, absolute maximum */
 
-#ifdef CONFIG_X86_5LEVEL
-/* __pgtable_l5_enabled needs to be in .data to avoid being cleared along with .bss */
-unsigned int __section(".data") __pgtable_l5_enabled;
-unsigned int __section(".data") pgdir_shift = 39;
-unsigned int __section(".data") ptrs_per_p4d = 1;
-#endif
-
 /* Buffer to preserve trampoline memory */
 static char trampoline_save[TRAMPOLINE_32BIT_SIZE];
 
@@ -127,11 +120,6 @@ asmlinkage void configure_5level_paging(struct boot_params *bp, void *pgtable)
 			native_cpuid_eax(0) >= 7 &&
 			(native_cpuid_ecx(7) & (1 << (X86_FEATURE_LA57 & 31)))) {
 		l5_required = true;
-
-		/* Initialize variables for 5-level paging */
-		__pgtable_l5_enabled = 1;
-		pgdir_shift = 48;
-		ptrs_per_p4d = 512;
 	}
 
 	/*
diff --git a/arch/x86/boot/startup/map_kernel.c b/arch/x86/boot/startup/map_kernel.c
index 905e8734b5a3..056de4766006 100644
--- a/arch/x86/boot/startup/map_kernel.c
+++ b/arch/x86/boot/startup/map_kernel.c
@@ -14,25 +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)
-{
-	if (!IS_ENABLED(CONFIG_X86_5LEVEL))
-		return false;
-
-	/*
-	 * 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;
-	pgdir_shift		= 48;
-	ptrs_per_p4d		= 512;
-
-	return true;
-}
-
 static unsigned long __head sme_postprocess_startup(struct boot_params *bp,
 						    pmdval_t *pmd,
 						    unsigned long p2v_offset)
@@ -102,7 +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 83cd6c4b9a3f..26deb6831235 100644
--- a/arch/x86/include/asm/pgtable_64_types.h
+++ b/arch/x86/include/asm/pgtable_64_types.h
@@ -21,8 +21,6 @@ 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;
-
 #ifdef CONFIG_X86_5LEVEL
 #ifndef pgtable_l5_enabled
 #define pgtable_l5_enabled() cpu_feature_enabled(X86_FEATURE_5LEVEL_PAGING)
@@ -31,9 +29,6 @@ extern unsigned int __pgtable_l5_enabled;
 #define pgtable_l5_enabled() 0
 #endif /* CONFIG_X86_5LEVEL */
 
-extern unsigned int pgdir_shift;
-extern unsigned int ptrs_per_p4d;
-
 #endif	/* !__ASSEMBLER__ */
 
 #define SHARED_KERNEL_PMD	0
@@ -43,7 +38,7 @@ extern unsigned int ptrs_per_p4d;
 /*
  * PGDIR_SHIFT determines what a top-level page table entry can map
  */
-#define PGDIR_SHIFT	pgdir_shift
+#define PGDIR_SHIFT	(pgtable_l5_enabled() ? 48 : 39)
 #define PTRS_PER_PGD	512
 
 /*
@@ -51,7 +46,7 @@ extern unsigned int ptrs_per_p4d;
  */
 #define P4D_SHIFT		39
 #define MAX_PTRS_PER_P4D	512
-#define PTRS_PER_P4D		ptrs_per_p4d
+#define PTRS_PER_P4D		(pgtable_l5_enabled() ? MAX_PTRS_PER_P4D : 1)
 #define P4D_SIZE		(_AC(1, UL) << P4D_SHIFT)
 #define P4D_MASK		(~(P4D_SIZE - 1))
 
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 84b5df539a94..68f6a31b4d8e 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -48,14 +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);
 
-#ifdef CONFIG_X86_5LEVEL
-unsigned int __pgtable_l5_enabled __ro_after_init;
-unsigned int pgdir_shift __ro_after_init = 39;
-EXPORT_SYMBOL(pgdir_shift);
-unsigned int ptrs_per_p4d __ro_after_init = 1;
-EXPORT_SYMBOL(ptrs_per_p4d);
-#endif
-
 #ifdef CONFIG_DYNAMIC_MEMORY_LAYOUT
 unsigned long page_offset_base __ro_after_init = __PAGE_OFFSET_BASE_L4;
 EXPORT_SYMBOL(page_offset_base);
-- 
2.49.0.1045.g170613ef41-goog