[tip: x86/boot] x86/startup_64: Defer assignment of 5-level paging global variables

[tip-bot2 for Ard Biesheuvel]

The following commit has been merged into the x86/boot branch of tip:

Commit-ID:     63bed96604205fa0b23c91d268df5f1f1b26faf6
Gitweb:        https://git.kernel.org/tip/63bed96604205fa0b23c91d268df5f1f1b26faf6
Author:        Ard Biesheuvel <ardb@xxxxxxxxxx>
AuthorDate:    Tue, 27 Feb 2024 16:19:10 +01:00
Committer:     Borislav Petkov (AMD) <bp@xxxxxxxxx>
CommitterDate: Mon, 04 Mar 2024 18:12:06 +01:00

x86/startup_64: Defer assignment of 5-level paging global variables

Assigning the 5-level paging related global variables from the earliest
C code using explicit references that use the 1:1 translation of memory
is unnecessary, as the startup code itself does not rely on them to
create the initial page tables, and this is all it should be doing. So
defer these assignments to the primary C entry code that executes via
the ordinary kernel virtual mapping.

Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Tested-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
Link: https://lore.kernel.org/r/20240227151907.387873-13-ardb+git@xxxxxxxxxx
---
 arch/x86/include/asm/pgtable_64_types.h |  2 +-
 arch/x86/kernel/head64.c                | 44 +++++++-----------------
 2 files changed, 15 insertions(+), 31 deletions(-)

diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
index 38b54b9..9053dfe 100644
--- a/arch/x86/include/asm/pgtable_64_types.h
+++ b/arch/x86/include/asm/pgtable_64_types.h
@@ -21,9 +21,9 @@ typedef unsigned long	pgprotval_t;
 typedef struct { pteval_t pte; } pte_t;
 typedef struct { pmdval_t pmd; } pmd_t;
 
-#ifdef CONFIG_X86_5LEVEL
 extern unsigned int __pgtable_l5_enabled;
 
+#ifdef CONFIG_X86_5LEVEL
 #ifdef USE_EARLY_PGTABLE_L5
 /*
  * cpu_feature_enabled() is not available in early boot code.
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index fd77a26..212e8e0 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -23,6 +23,7 @@
 #include <linux/pgtable.h>
 
 #include <asm/asm.h>
+#include <asm/page_64.h>
 #include <asm/processor.h>
 #include <asm/proto.h>
 #include <asm/smp.h>
@@ -68,24 +69,11 @@ unsigned long vmemmap_base __ro_after_init = __VMEMMAP_BASE_L4;
 EXPORT_SYMBOL(vmemmap_base);
 #endif
 
-#ifdef CONFIG_X86_5LEVEL
-static void __head *fixup_pointer(void *ptr, unsigned long physaddr)
-{
-	return ptr - (void *)_text + (void *)physaddr;
-}
-
-static unsigned long __head *fixup_long(void *ptr, unsigned long physaddr)
+static inline bool check_la57_support(void)
 {
-	return fixup_pointer(ptr, physaddr);
-}
-
-static unsigned int __head *fixup_int(void *ptr, unsigned long physaddr)
-{
-	return fixup_pointer(ptr, physaddr);
-}
+	if (!IS_ENABLED(CONFIG_X86_5LEVEL))
+		return false;
 
-static bool __head check_la57_support(unsigned long physaddr)
-{
 	/*
 	 * 5-level paging is detected and enabled at kernel decompression
 	 * stage. Only check if it has been enabled there.
@@ -93,21 +81,8 @@ static bool __head check_la57_support(unsigned long physaddr)
 	if (!(native_read_cr4() & X86_CR4_LA57))
 		return false;
 
-	*fixup_int(&__pgtable_l5_enabled, physaddr) = 1;
-	*fixup_int(&pgdir_shift, physaddr) = 48;
-	*fixup_int(&ptrs_per_p4d, physaddr) = 512;
-	*fixup_long(&page_offset_base, physaddr) = __PAGE_OFFSET_BASE_L5;
-	*fixup_long(&vmalloc_base, physaddr) = __VMALLOC_BASE_L5;
-	*fixup_long(&vmemmap_base, physaddr) = __VMEMMAP_BASE_L5;
-
 	return true;
 }
-#else
-static bool __head check_la57_support(unsigned long physaddr)
-{
-	return false;
-}
-#endif
 
 static unsigned long __head sme_postprocess_startup(struct boot_params *bp, pmdval_t *pmd)
 {
@@ -171,7 +146,7 @@ unsigned long __head __startup_64(unsigned long physaddr,
 	bool la57;
 	int i;
 
-	la57 = check_la57_support(physaddr);
+	la57 = check_la57_support();
 
 	/* Is the address too large? */
 	if (physaddr >> MAX_PHYSMEM_BITS)
@@ -456,6 +431,15 @@ asmlinkage __visible void __init __noreturn x86_64_start_kernel(char * real_mode
 				(__START_KERNEL & PGDIR_MASK)));
 	BUILD_BUG_ON(__fix_to_virt(__end_of_fixed_addresses) <= MODULES_END);
 
+	if (check_la57_support()) {
+		__pgtable_l5_enabled	= 1;
+		pgdir_shift		= 48;
+		ptrs_per_p4d		= 512;
+		page_offset_base	= __PAGE_OFFSET_BASE_L5;
+		vmalloc_base		= __VMALLOC_BASE_L5;
+		vmemmap_base		= __VMEMMAP_BASE_L5;
+	}
+
 	cr4_init_shadow();
 
 	/* Kill off the identity-map trampoline */