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

Ard Biesheuvel
2022-06-24T15:08:31Z

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@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);