[RFC PATCH v2 11/18] 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.

Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
---
 arch/arm64/include/asm/memory.h | 4 ++++
 arch/arm64/kernel/head.S        | 7 +++----
 arch/arm64/mm/mmu.c             | 2 ++
 3 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 2f1a48be11cf..c989f6bf5426 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		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 44e2e39046a9..836237289ffb 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -283,19 +283,18 @@ SYM_FUNC_START_LOCAL(create_idmap)
 	adrp	x0, idmap_pg_dir
 	adrp	x3, _text			// __pa(_text)
 
-#ifdef CONFIG_ARM64_VA_BITS_52
+#if (VA_BITS > 48)
 	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
-
+#endif
 	/*
 	 * 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
@@ -725,7 +724,7 @@ 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/mmu.c b/arch/arm64/mm/mmu.c
index 20dd95a750bc..8933d4f72427 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -45,8 +45,10 @@
 
 u64 idmap_t0sz = TCR_T0SZ(VA_BITS_MIN);
 
+#if (VA_BITS > 48)
 u64 __section(".mmuoff.data.write") vabits_actual;
 EXPORT_SYMBOL(vabits_actual);
+#endif
 
 u64 kimage_voffset __ro_after_init;
 EXPORT_SYMBOL(kimage_voffset);
-- 
2.30.2