arm64/mm: Drop configurable 48-bit physical address space limit

Currently, the maximum supported physical address space can be
configured as either 48 bits or 52 bits. The only remaining difference
between these in practice is that the former omits the masking and
shifting required to construct TTBR and PTE values, which carry bits #48
and higher disjoint from the rest of the physical address.

The overhead of performing these additional calculations is negligible,
and so there is little reason to retain support for two different
configurations, and we can simply support whatever the hardware
supports.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20241212081841.2168124-14-ardb+git@google.com
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/Kconfig

@@ -1416,38 +1416,9 @@ config ARM64_VA_BITS
 	default 48 if ARM64_VA_BITS_48
 	default 52 if ARM64_VA_BITS_52
 
-choice
-	prompt "Physical address space size"
-	default ARM64_PA_BITS_48
-	help
-	  Choose the maximum physical address range that the kernel will
-	  support.
-
-config ARM64_PA_BITS_48
-	bool "48-bit"
-	depends on ARM64_64K_PAGES || !ARM64_VA_BITS_52
-
-config ARM64_PA_BITS_52
-	bool "52-bit"
-	depends on ARM64_64K_PAGES || ARM64_VA_BITS_52
-	help
-	  Enable support for a 52-bit physical address space, introduced as
-	  part of the ARMv8.2-LPA extension.
-
-	  With this enabled, the kernel will also continue to work on CPUs that
-	  do not support ARMv8.2-LPA, but with some added memory overhead (and
-	  minor performance overhead).
-
-endchoice
-
-config ARM64_PA_BITS
-	int
-	default 48 if ARM64_PA_BITS_48
-	default 52 if ARM64_PA_BITS_52
-
 config ARM64_LPA2
 	def_bool y
-	depends on ARM64_PA_BITS_52 && !ARM64_64K_PAGES
+	depends on !ARM64_64K_PAGES
 
 choice
 	prompt "Endianness"

arch/arm64/include/asm/assembler.h

@@ -342,14 +342,13 @@ alternative_cb_end
 	mrs	\tmp0, ID_AA64MMFR0_EL1
 	// Narrow PARange to fit the PS field in TCR_ELx
 	ubfx	\tmp0, \tmp0, #ID_AA64MMFR0_EL1_PARANGE_SHIFT, #3
-	mov	\tmp1, #ID_AA64MMFR0_EL1_PARANGE_MAX
 #ifdef CONFIG_ARM64_LPA2
 alternative_if_not ARM64_HAS_VA52
 	mov	\tmp1, #ID_AA64MMFR0_EL1_PARANGE_48
-alternative_else_nop_endif
-#endif
 	cmp	\tmp0, \tmp1
 	csel	\tmp0, \tmp1, \tmp0, hi
+alternative_else_nop_endif
+#endif
 	bfi	\tcr, \tmp0, \pos, #3
 	.endm
 
@@ -599,21 +598,13 @@ alternative_endif
  * 	ttbr:	returns the TTBR value
  */
 	.macro	phys_to_ttbr, ttbr, phys
-#ifdef CONFIG_ARM64_PA_BITS_52
 	orr	\ttbr, \phys, \phys, lsr #46
 	and	\ttbr, \ttbr, #TTBR_BADDR_MASK_52
-#else
-	mov	\ttbr, \phys
-#endif
 	.endm
 
 	.macro	phys_to_pte, pte, phys
-#ifdef CONFIG_ARM64_PA_BITS_52
 	orr	\pte, \phys, \phys, lsr #PTE_ADDR_HIGH_SHIFT
 	and	\pte, \pte, #PHYS_TO_PTE_ADDR_MASK
-#else
-	mov	\pte, \phys
-#endif
 	.endm
 
 /*

arch/arm64/include/asm/cpufeature.h

@@ -884,9 +884,8 @@ static inline u32 id_aa64mmfr0_parange_to_phys_shift(int parange)
 	 * However, by the "D10.1.4 Principles of the ID scheme
 	 * for fields in ID registers", ARM DDI 0487C.a, any new
 	 * value is guaranteed to be higher than what we know already.
-	 * As a safe limit, we return the limit supported by the kernel.
 	 */
-	default: return CONFIG_ARM64_PA_BITS;
+	default: return 52;
 	}
 }
 

arch/arm64/include/asm/kvm_pgtable.h

@@ -30,8 +30,7 @@
 
 static inline u64 kvm_get_parange_max(void)
 {
-	if (kvm_lpa2_is_enabled() ||
+	if (kvm_lpa2_is_enabled() || PAGE_SHIFT == 16)
-	   (IS_ENABLED(CONFIG_ARM64_PA_BITS_52) && PAGE_SHIFT == 16))
 		return ID_AA64MMFR0_EL1_PARANGE_52;
 	else
 		return ID_AA64MMFR0_EL1_PARANGE_48;

arch/arm64/include/asm/pgtable-hwdef.h

@@ -176,7 +176,6 @@
 #define PTE_SWBITS_MASK		_AT(pteval_t, (BIT(63) | GENMASK(58, 55)))
 
 #define PTE_ADDR_LOW		(((_AT(pteval_t, 1) << (50 - PAGE_SHIFT)) - 1) << PAGE_SHIFT)
-#ifdef CONFIG_ARM64_PA_BITS_52
 #ifdef CONFIG_ARM64_64K_PAGES
 #define PTE_ADDR_HIGH		(_AT(pteval_t, 0xf) << 12)
 #define PTE_ADDR_HIGH_SHIFT	36
@@ -186,7 +185,6 @@
 #define PTE_ADDR_HIGH_SHIFT	42
 #define PHYS_TO_PTE_ADDR_MASK	GENMASK_ULL(49, 8)
 #endif
-#endif
 
 /*
  * AttrIndx[2:0] encoding (mapping attributes defined in the MAIR* registers).
@@ -327,12 +325,10 @@
 /*
  * TTBR.
  */
-#ifdef CONFIG_ARM64_PA_BITS_52
 /*
- * TTBR_ELx[1] is RES0 in this configuration.
+ * TTBR_ELx[1] is RES0 when using 52-bit physical addressing
  */
 #define TTBR_BADDR_MASK_52	GENMASK_ULL(47, 2)
-#endif
 
 #ifdef CONFIG_ARM64_VA_BITS_52
 /* Must be at least 64-byte aligned to prevent corruption of the TTBR */

arch/arm64/include/asm/pgtable-prot.h

@@ -81,7 +81,7 @@ extern unsigned long prot_ns_shared;
 #define lpa2_is_enabled()	false
 #define PTE_MAYBE_SHARED	PTE_SHARED
 #define PMD_MAYBE_SHARED	PMD_SECT_S
-#define PHYS_MASK_SHIFT		(CONFIG_ARM64_PA_BITS)
+#define PHYS_MASK_SHIFT		(52)
 #else
 static inline bool __pure lpa2_is_enabled(void)
 {
@@ -90,7 +90,7 @@ static inline bool __pure lpa2_is_enabled(void)
 
 #define PTE_MAYBE_SHARED	(lpa2_is_enabled() ? 0 : PTE_SHARED)
 #define PMD_MAYBE_SHARED	(lpa2_is_enabled() ? 0 : PMD_SECT_S)
-#define PHYS_MASK_SHIFT		(lpa2_is_enabled() ? CONFIG_ARM64_PA_BITS : 48)
+#define PHYS_MASK_SHIFT		(lpa2_is_enabled() ? 52 : 48)
 #endif
 
 /*

arch/arm64/include/asm/pgtable.h

@@ -69,10 +69,9 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
 	pr_err("%s:%d: bad pte %016llx.\n", __FILE__, __LINE__, pte_val(e))
 
 /*
- * Macros to convert between a physical address and its placement in a
+ * Helpers to convert between a physical address and its placement in a
  * page table entry, taking care of 52-bit addresses.
  */
-#ifdef CONFIG_ARM64_PA_BITS_52
 static inline phys_addr_t __pte_to_phys(pte_t pte)
 {
 	pte_val(pte) &= ~PTE_MAYBE_SHARED;
@@ -83,10 +82,6 @@ static inline pteval_t __phys_to_pte_val(phys_addr_t phys)
 {
 	return (phys | (phys >> PTE_ADDR_HIGH_SHIFT)) & PHYS_TO_PTE_ADDR_MASK;
 }
-#else
-#define __pte_to_phys(pte)	(pte_val(pte) & PTE_ADDR_LOW)
-#define __phys_to_pte_val(phys)	(phys)
-#endif
 
 #define pte_pfn(pte)		(__pte_to_phys(pte) >> PAGE_SHIFT)
 #define pfn_pte(pfn,prot)	\
@@ -1495,11 +1490,7 @@ static inline void update_mmu_cache_range(struct vm_fault *vmf,
 	update_mmu_cache_range(NULL, vma, addr, ptep, 1)
 #define update_mmu_cache_pmd(vma, address, pmd) do { } while (0)
 
-#ifdef CONFIG_ARM64_PA_BITS_52
 #define phys_to_ttbr(addr)	(((addr) | ((addr) >> 46)) & TTBR_BADDR_MASK_52)
-#else
-#define phys_to_ttbr(addr)	(addr)
-#endif
 
 /*
  * On arm64 without hardware Access Flag, copying from user will fail because

arch/arm64/include/asm/sysreg.h

@@ -916,12 +916,6 @@
 #define ID_AA64MMFR0_EL1_TGRAN_2_SUPPORTED_LPA2		0x3
 #define ID_AA64MMFR0_EL1_TGRAN_2_SUPPORTED_MAX		0x7
 
-#ifdef CONFIG_ARM64_PA_BITS_52
-#define ID_AA64MMFR0_EL1_PARANGE_MAX	ID_AA64MMFR0_EL1_PARANGE_52
-#else
-#define ID_AA64MMFR0_EL1_PARANGE_MAX	ID_AA64MMFR0_EL1_PARANGE_48
-#endif
-
 #if defined(CONFIG_ARM64_4K_PAGES)
 #define ID_AA64MMFR0_EL1_TGRAN_SHIFT		ID_AA64MMFR0_EL1_TGRAN4_SHIFT
 #define ID_AA64MMFR0_EL1_TGRAN_LPA2		ID_AA64MMFR0_EL1_TGRAN4_52_BIT

arch/arm64/mm/pgd.c

@@ -48,20 +48,21 @@ void pgd_free(struct mm_struct *mm, pgd_t *pgd)
 
 void __init pgtable_cache_init(void)
 {
+	unsigned int pgd_size = PGD_SIZE;
+
 	if (pgdir_is_page_size())
 		return;
 
-#ifdef CONFIG_ARM64_PA_BITS_52
 	/*
 	 * With 52-bit physical addresses, the architecture requires the
 	 * top-level table to be aligned to at least 64 bytes.
 	 */
-	BUILD_BUG_ON(PGD_SIZE < 64);
+	if (PHYS_MASK_SHIFT >= 52)
-#endif
+		pgd_size = max(pgd_size, 64);
 
 	/*
 	 * Naturally aligned pgds required by the architecture.
 	 */
-	pgd_cache = kmem_cache_create("pgd_cache", PGD_SIZE, PGD_SIZE,
+	pgd_cache = kmem_cache_create("pgd_cache", pgd_size, pgd_size,
 				      SLAB_PANIC, NULL);
 }

arch/arm64/mm/proc.S

@@ -197,10 +197,8 @@ SYM_FUNC_ALIAS(__pi_idmap_cpu_replace_ttbr1, idmap_cpu_replace_ttbr1)
 
 	.macro	pte_to_phys, phys, pte
 	and	\phys, \pte, #PTE_ADDR_LOW
-#ifdef CONFIG_ARM64_PA_BITS_52
 	and	\pte, \pte, #PTE_ADDR_HIGH
 	orr	\phys, \phys, \pte, lsl #PTE_ADDR_HIGH_SHIFT
-#endif
 	.endm
 
 	.macro	kpti_mk_tbl_ng, type, num_entries

scripts/gdb/linux/constants.py.in

@@ -141,7 +141,6 @@ LX_CONFIG(CONFIG_ARM64_4K_PAGES)
 LX_CONFIG(CONFIG_ARM64_16K_PAGES)
 LX_CONFIG(CONFIG_ARM64_64K_PAGES)
 if IS_BUILTIN(CONFIG_ARM64):
-    LX_VALUE(CONFIG_ARM64_PA_BITS)
     LX_VALUE(CONFIG_ARM64_VA_BITS)
     LX_VALUE(CONFIG_PAGE_SHIFT)
     LX_VALUE(CONFIG_ARCH_FORCE_MAX_ORDER)

tools/arch/arm64/include/asm/sysreg.h

@@ -574,12 +574,6 @@
 #define ID_AA64MMFR0_EL1_TGRAN_2_SUPPORTED_MIN		0x2
 #define ID_AA64MMFR0_EL1_TGRAN_2_SUPPORTED_MAX		0x7
 
-#ifdef CONFIG_ARM64_PA_BITS_52
-#define ID_AA64MMFR0_EL1_PARANGE_MAX	ID_AA64MMFR0_EL1_PARANGE_52
-#else
-#define ID_AA64MMFR0_EL1_PARANGE_MAX	ID_AA64MMFR0_EL1_PARANGE_48
-#endif
-
 #if defined(CONFIG_ARM64_4K_PAGES)
 #define ID_AA64MMFR0_EL1_TGRAN_SHIFT		ID_AA64MMFR0_EL1_TGRAN4_SHIFT
 #define ID_AA64MMFR0_EL1_TGRAN_SUPPORTED_MIN	ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MIN