arm64: add FIXADDR_TOT_{START,SIZE}

Currently arm64's FIXADDR_{START,SIZE} definitions only cover the
runtime fixmap slots (and not the boot-time fixmap slots), but the code
for creating the fixmap assumes that these definitions cover the entire
fixmap range. This means that the ptdump boundaries are reported in a
misleading way, missing the VA region of the runtime slots. In theory
this could also cause the fixmap creation to go wrong if the boot-time
fixmap slots end up spilling into a separate PMD entry, though luckily
this is not currently the case in any configuration.

While it seems like we could extend FIXADDR_{START,SIZE} to cover the
entire fixmap area, core code relies upon these *only* covering the
runtime slots. For example, fix_to_virt() and virt_to_fix() try to
reject manipulation of the boot-time slots based upon
FIXADDR_{START,SIZE}, while __fix_to_virt() and __virt_to_fix() can
handle any fixmap slot.

This patch follows the lead of x86 in commit:

  55f49fcb ("x86/mm: Fix overlap of i386 CPU_ENTRY_AREA with FIX_BTMAP")

... and add new FIXADDR_TOT_{START,SIZE} definitions which cover the
entire fixmap area, using these for the fixmap creation and ptdump code.

As the boot-time fixmap slots are now rejected by fix_to_virt(),
the early_fixmap_init() code is changed to consistently use
__fix_to_virt(), as it already does in a few cases.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Link: https://lore.kernel.org/r/20230406152759.4164229-2-mark.rutland@arm.comSigned-off-by: Will Deacon <will@kernel.org>

arch/arm64/include/asm/fixmap.h

@@ -97,6 +97,8 @@ enum fixed_addresses {
 
 #define FIXADDR_SIZE		(__end_of_permanent_fixed_addresses << PAGE_SHIFT)
 #define FIXADDR_START		(FIXADDR_TOP - FIXADDR_SIZE)
+#define FIXADDR_TOT_SIZE	(__end_of_fixed_addresses << PAGE_SHIFT)
+#define FIXADDR_TOT_START	(FIXADDR_TOP - FIXADDR_TOT_SIZE)
 
 #define FIXMAP_PAGE_IO     __pgprot(PROT_DEVICE_nGnRE)
 

arch/arm64/mm/mmu.c

@@ -795,14 +795,14 @@ static void __init map_kernel(pgd_t *pgdp)
 			   &vmlinux_initdata, 0, VM_NO_GUARD);
 	map_kernel_segment(pgdp, _data, _end, PAGE_KERNEL, &vmlinux_data, 0, 0);
 
-	if (!READ_ONCE(pgd_val(*pgd_offset_pgd(pgdp, FIXADDR_START)))) {
+	if (!READ_ONCE(pgd_val(*pgd_offset_pgd(pgdp, FIXADDR_TOT_START)))) {
 		/*
 		 * The fixmap falls in a separate pgd to the kernel, and doesn't
 		 * live in the carveout for the swapper_pg_dir. We can simply
 		 * re-use the existing dir for the fixmap.
 		 */
-		set_pgd(pgd_offset_pgd(pgdp, FIXADDR_START),
-			READ_ONCE(*pgd_offset_k(FIXADDR_START)));
+		set_pgd(pgd_offset_pgd(pgdp, FIXADDR_TOT_START),
+			READ_ONCE(*pgd_offset_k(FIXADDR_TOT_START)));
 	} else if (CONFIG_PGTABLE_LEVELS > 3) {
 		pgd_t *bm_pgdp;
 		p4d_t *bm_p4dp;
@@ -814,9 +814,9 @@ static void __init map_kernel(pgd_t *pgdp)
 		 * entry instead.
 		 */
 		BUG_ON(!IS_ENABLED(CONFIG_ARM64_16K_PAGES));
-		bm_pgdp = pgd_offset_pgd(pgdp, FIXADDR_START);
-		bm_p4dp = p4d_offset(bm_pgdp, FIXADDR_START);
-		bm_pudp = pud_set_fixmap_offset(bm_p4dp, FIXADDR_START);
+		bm_pgdp = pgd_offset_pgd(pgdp, FIXADDR_TOT_START);
+		bm_p4dp = p4d_offset(bm_pgdp, FIXADDR_TOT_START);
+		bm_pudp = pud_set_fixmap_offset(bm_p4dp, FIXADDR_TOT_START);
 		pud_populate(&init_mm, bm_pudp, lm_alias(bm_pmd));
 		pud_clear_fixmap();
 	} else {
@@ -1275,7 +1275,7 @@ void __init early_fixmap_init(void)
 	p4d_t *p4dp, p4d;
 	pud_t *pudp;
 	pmd_t *pmdp;
-	unsigned long addr = FIXADDR_START;
+	unsigned long addr = FIXADDR_TOT_START;
 
 	pgdp = pgd_offset_k(addr);
 	p4dp = p4d_offset(pgdp, addr);
@@ -1306,16 +1306,16 @@ void __init early_fixmap_init(void)
 	BUILD_BUG_ON((__fix_to_virt(FIX_BTMAP_BEGIN) >> PMD_SHIFT)
 		     != (__fix_to_virt(FIX_BTMAP_END) >> PMD_SHIFT));
 
-	if ((pmdp != fixmap_pmd(fix_to_virt(FIX_BTMAP_BEGIN)))
-	     || pmdp != fixmap_pmd(fix_to_virt(FIX_BTMAP_END))) {
+	if ((pmdp != fixmap_pmd(__fix_to_virt(FIX_BTMAP_BEGIN)))
+	     || pmdp != fixmap_pmd(__fix_to_virt(FIX_BTMAP_END))) {
 		WARN_ON(1);
 		pr_warn("pmdp %p != %p, %p\n",
-			pmdp, fixmap_pmd(fix_to_virt(FIX_BTMAP_BEGIN)),
-			fixmap_pmd(fix_to_virt(FIX_BTMAP_END)));
+			pmdp, fixmap_pmd(__fix_to_virt(FIX_BTMAP_BEGIN)),
+			fixmap_pmd(__fix_to_virt(FIX_BTMAP_END)));
 		pr_warn("fix_to_virt(FIX_BTMAP_BEGIN): %08lx\n",
-			fix_to_virt(FIX_BTMAP_BEGIN));
+			__fix_to_virt(FIX_BTMAP_BEGIN));
 		pr_warn("fix_to_virt(FIX_BTMAP_END):   %08lx\n",
-			fix_to_virt(FIX_BTMAP_END));
+			__fix_to_virt(FIX_BTMAP_END));
 
 		pr_warn("FIX_BTMAP_END:       %d\n", FIX_BTMAP_END);
 		pr_warn("FIX_BTMAP_BEGIN:     %d\n", FIX_BTMAP_BEGIN);

arch/arm64/mm/ptdump.c

@@ -45,7 +45,7 @@ static struct addr_marker address_markers[] = {
 	{ MODULES_END,			"Modules end" },
 	{ VMALLOC_START,		"vmalloc() area" },
 	{ VMALLOC_END,			"vmalloc() end" },
-	{ FIXADDR_START,		"Fixmap start" },
+	{ FIXADDR_TOT_START,		"Fixmap start" },
 	{ FIXADDR_TOP,			"Fixmap end" },
 	{ PCI_IO_START,			"PCI I/O start" },
 	{ PCI_IO_END,			"PCI I/O end" },