[PATCH v5 02/21] arm64: mm: make vabits_actual a build time constant if possible

[Ard Biesheuvel]

Currently, we only support 52-bit virtual addressing on 64k pages
configurations, and in all other cases, vabits_actual is guaranteed to
equal VA_BITS (== VA_BITS_MIN). So get rid of the variable entirely in
that case.

While at it, move the assignment out of the asm entry code - it has no
need to be there.

Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
---
 arch/arm64/include/asm/memory.h |  4 ++++
 arch/arm64/kernel/head.S        | 15 +--------------
 arch/arm64/mm/init.c            | 15 ++++++++++++++-
 arch/arm64/mm/mmu.c             |  4 +++-
 4 files changed, 22 insertions(+), 16 deletions(-)

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 0af70d9abede..c751cd9b94f8 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -174,7 +174,11 @@
 #include <linux/types.h>
 #include <asm/bug.h>
 
+#if VA_BITS > 48
 extern u64			vabits_actual;
+#else
+#define vabits_actual		((u64)VA_BITS)
+#endif
 
 extern s64			memstart_addr;
 /* PHYS_OFFSET - the physical address of the start of memory. */
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 1cdecce552bb..dc07858eb673 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -293,19 +293,6 @@ SYM_FUNC_START_LOCAL(__create_page_tables)
 	adrp	x0, idmap_pg_dir
 	adrp	x3, __idmap_text_start		// __pa(__idmap_text_start)
 
-#ifdef CONFIG_ARM64_VA_BITS_52
-	mrs_s	x6, SYS_ID_AA64MMFR2_EL1
-	and	x6, x6, #(0xf << ID_AA64MMFR2_LVA_SHIFT)
-	mov	x5, #52
-	cbnz	x6, 1f
-#endif
-	mov	x5, #VA_BITS_MIN
-1:
-	adr_l	x6, vabits_actual
-	str	x5, [x6]
-	dmb	sy
-	dc	ivac, x6		// Invalidate potentially stale cache line
-
 	/*
 	 * VA_BITS may be too small to allow for an ID mapping to be created
 	 * that covers system RAM if that is located sufficiently high in the
@@ -713,7 +700,7 @@ SYM_FUNC_START(__enable_mmu)
 SYM_FUNC_END(__enable_mmu)
 
 SYM_FUNC_START(__cpu_secondary_check52bitva)
-#ifdef CONFIG_ARM64_VA_BITS_52
+#if VA_BITS > 48
 	ldr_l	x0, vabits_actual
 	cmp	x0, #52
 	b.ne	2f
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 339ee84e5a61..1faa6760895e 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -265,7 +265,20 @@ early_param("mem", early_mem);
 
 void __init arm64_memblock_init(void)
 {
-	s64 linear_region_size = PAGE_END - _PAGE_OFFSET(vabits_actual);
+	s64 linear_region_size;
+
+#if VA_BITS > 48
+	if (cpuid_feature_extract_unsigned_field(
+				read_sysreg_s(SYS_ID_AA64MMFR2_EL1),
+				ID_AA64MMFR2_LVA_SHIFT))
+		vabits_actual = VA_BITS;
+
+	/* make the variable visible to secondaries with the MMU off */
+	dcache_clean_inval_poc((u64)&vabits_actual,
+			       (u64)&vabits_actual + sizeof(vabits_actual));
+#endif
+
+	linear_region_size = PAGE_END - _PAGE_OFFSET(vabits_actual);
 
 	/*
 	 * Corner case: 52-bit VA capable systems running KVM in nVHE mode may
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 7148928e3932..a6392656d589 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -46,8 +46,10 @@
 u64 idmap_t0sz = TCR_T0SZ(VA_BITS_MIN);
 u64 idmap_ptrs_per_pgd = PTRS_PER_PGD;
 
-u64 __section(".mmuoff.data.write") vabits_actual;
+#if VA_BITS > 48
+u64 vabits_actual __ro_after_init = VA_BITS_MIN;
 EXPORT_SYMBOL(vabits_actual);
+#endif
 
 u64 kimage_vaddr __ro_after_init = (u64)&_text;
 EXPORT_SYMBOL(kimage_vaddr);
-- 
2.35.1