x86/boot/64: Use RIP_REL_REF() to access early_top_pgt[]

early_top_pgt[] is assigned from code that executes from a 1:1 mapping
so it cannot use a plain access from C. Replace the use of
fixup_pointer() with RIP_REL_REF(), which is better and simpler.

For legibility and to align with the code that populates the lower page
table levels, statically initialize the root level page table with an
entry pointing to level3_kernel_pgt[], and overwrite it when needed to
enable 5-level paging.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240221113506.2565718-24-ardb+git@google.com

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 7e2c9b581d582e3132bcf72dc6760df6835d81d9..72351c3121a62f283f1b4028b3547b53e5c9165b 100644 (file)
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -77,6 +77,7 @@ static struct desc_struct startup_gdt[GDT_ENTRIES] __initdata = {
        [GDT_ENTRY_KERNEL_DS]           = GDT_ENTRY_INIT(DESC_DATA64, 0, 0xfffff),
 };
 
+#ifdef CONFIG_X86_5LEVEL
 static void __head *fixup_pointer(void *ptr, unsigned long physaddr)
 {
        return ptr - (void *)_text + (void *)physaddr;
@@ -87,7 +88,6 @@ static unsigned long __head *fixup_long(void *ptr, unsigned long physaddr)
        return fixup_pointer(ptr, physaddr);
 }
 
-#ifdef CONFIG_X86_5LEVEL
 static unsigned int __head *fixup_int(void *ptr, unsigned long physaddr)
 {
        return fixup_pointer(ptr, physaddr);
@@ -165,14 +165,14 @@ static unsigned long __head sme_postprocess_startup(struct boot_params *bp, pmdv
  * doesn't have to generate PC-relative relocations when accessing globals from
  * that function. Clang actually does not generate them, which leads to
  * boot-time crashes. To work around this problem, every global pointer must
- * be adjusted using fixup_pointer().
+ * be accessed using RIP_REL_REF().
  */
 unsigned long __head __startup_64(unsigned long physaddr,
                                  struct boot_params *bp)
 {
        pmd_t (*early_pgts)[PTRS_PER_PMD] = RIP_REL_REF(early_dynamic_pgts);
-       unsigned long load_delta, *p;
        unsigned long pgtable_flags;
+       unsigned long load_delta;
        pgdval_t *pgd;
        p4dval_t *p4d;
        pudval_t *pud;
@@ -202,17 +202,14 @@ unsigned long __head __startup_64(unsigned long physaddr,
 
        /* Fixup the physical addresses in the page table */
 
-       pgd = fixup_pointer(early_top_pgt, physaddr);
-       p = pgd + pgd_index(__START_KERNEL_map);
-       if (la57)
-               *p = (unsigned long)level4_kernel_pgt;
-       else
-               *p = (unsigned long)level3_kernel_pgt;
-       *p += _PAGE_TABLE_NOENC - __START_KERNEL_map + load_delta;
+       pgd = &RIP_REL_REF(early_top_pgt)->pgd;
+       pgd[pgd_index(__START_KERNEL_map)] += load_delta;
 
        if (la57) {
-               p4d = fixup_pointer(level4_kernel_pgt, physaddr);
-               p4d[511] += load_delta;
+               p4d = (p4dval_t *)&RIP_REL_REF(level4_kernel_pgt);
+               p4d[MAX_PTRS_PER_P4D - 1] += load_delta;
+
+               pgd[pgd_index(__START_KERNEL_map)] = (pgdval_t)p4d | _PAGE_TABLE_NOENC;
        }
 
        RIP_REL_REF(level3_kernel_pgt)[PTRS_PER_PUD - 2].pud += load_delta;

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index e09cf0b09141dcf7aca1eab2858a8e58888c8118..d295bf68bf944f231fa2876e62015f898b534324 100644 (file)
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -624,7 +624,8 @@ SYM_CODE_END(vc_no_ghcb)
        .balign 4
 
 SYM_DATA_START_PTI_ALIGNED(early_top_pgt)
-       .fill   512,8,0
+       .fill   511,8,0
+       .quad   level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE_NOENC
        .fill   PTI_USER_PGD_FILL,8,0
 SYM_DATA_END(early_top_pgt)