[PATCH 2/2] arm64: mm: extend linear region for 52-bit VA configurations
Ard Biesheuvel
ardb at kernel.org
Tue Oct 6 18:49:53 EDT 2020
For historical reasons, the arm64 kernel VA space is configured as two
equally sized halves, i.e., on a 48-bit VA build, the VA space is split
into a 47-bit vmalloc region and a 47-bit linear region.
When support for 52-bit virtual addressing was added, this equal split
was kept, resulting in a substantial waste of virtual address space in
the linear region:
48-bit VA 52-bit VA
0xffff_ffff_ffff_ffff +-------------+ +-------------+
| vmalloc | | vmalloc |
0xffff_8000_0000_0000 +-------------+ _PAGE_END(48) +-------------+
| linear | : :
0xffff_0000_0000_0000 +-------------+ : :
: : : :
: : : :
: : : :
: : : currently :
: unusable : : :
: : : unused :
: by : : :
: : : :
: hardware : : :
: : : :
0xfff8_0000_0000_0000 : : _PAGE_END(52) +-------------+
: : | |
: : | |
: : | |
: : | |
: : | |
: unusable : | |
: : | linear |
: by : | |
: : | region |
: hardware : | |
: : | |
: : | |
: : | |
: : | |
: : | |
: : | |
0xfff0_0000_0000_0000 +-------------+ PAGE_OFFSET +-------------+
As illustrated above, the 52-bit VA kernel uses 47 bits for the vmalloc
space (as before), to ensure that a single 64k granule kernel image can
support any 64k granule capable system, regardless of whether it supports
the 52-bit virtual addressing extension. However, due to the fact that
the VA space is still split in equal halves, the linear region is only
2^51 bytes in size, wasting almost half of the 52-bit VA space.
Let's fix this, by abandoning the equal split, and simply assigning all
VA space outside of the vmalloc region to the linear region.
The KASAN shadow region is reconfigured so that it ends at the start of
the vmalloc region, and grows downwards. That way, the arrangement of
the vmalloc space (which contains kernel mappings, modules, BPF region,
the vmemmap array etc) is identical between non-KASAN and KASAN builds,
which aids debugging.
Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
---
Documentation/arm64/kasan-offsets.sh | 3 +--
arch/arm64/Kconfig | 20 ++++++++++----------
arch/arm64/include/asm/memory.h | 8 ++++----
arch/arm64/mm/init.c | 2 +-
4 files changed, 16 insertions(+), 17 deletions(-)
diff --git a/Documentation/arm64/kasan-offsets.sh b/Documentation/arm64/kasan-offsets.sh
index 2b7a021db363..2dc5f9e18039 100644
--- a/Documentation/arm64/kasan-offsets.sh
+++ b/Documentation/arm64/kasan-offsets.sh
@@ -1,12 +1,11 @@
#!/bin/sh
# Print out the KASAN_SHADOW_OFFSETS required to place the KASAN SHADOW
-# start address at the mid-point of the kernel VA space
+# start address at the top of the linear region
print_kasan_offset () {
printf "%02d\t" $1
printf "0x%08x00000000\n" $(( (0xffffffff & (-1 << ($1 - 1 - 32))) \
- + (1 << ($1 - 32 - $2)) \
- (1 << (64 - 32 - $2)) ))
}
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 6d232837cbee..896a46a71d23 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -321,16 +321,16 @@ config BROKEN_GAS_INST
config KASAN_SHADOW_OFFSET
hex
depends on KASAN
- default 0xdfffa00000000000 if (ARM64_VA_BITS_48 || ARM64_VA_BITS_52) && !KASAN_SW_TAGS
- default 0xdfffd00000000000 if ARM64_VA_BITS_47 && !KASAN_SW_TAGS
- default 0xdffffe8000000000 if ARM64_VA_BITS_42 && !KASAN_SW_TAGS
- default 0xdfffffd000000000 if ARM64_VA_BITS_39 && !KASAN_SW_TAGS
- default 0xdffffffa00000000 if ARM64_VA_BITS_36 && !KASAN_SW_TAGS
- default 0xefff900000000000 if (ARM64_VA_BITS_48 || ARM64_VA_BITS_52) && KASAN_SW_TAGS
- default 0xefffc80000000000 if ARM64_VA_BITS_47 && KASAN_SW_TAGS
- default 0xeffffe4000000000 if ARM64_VA_BITS_42 && KASAN_SW_TAGS
- default 0xefffffc800000000 if ARM64_VA_BITS_39 && KASAN_SW_TAGS
- default 0xeffffff900000000 if ARM64_VA_BITS_36 && KASAN_SW_TAGS
+ default 0xdfff800000000000 if (ARM64_VA_BITS_48 || ARM64_VA_BITS_52) && !KASAN_SW_TAGS
+ default 0xdfffc00000000000 if ARM64_VA_BITS_47 && !KASAN_SW_TAGS
+ default 0xdffffe0000000000 if ARM64_VA_BITS_42 && !KASAN_SW_TAGS
+ default 0xdfffffc000000000 if ARM64_VA_BITS_39 && !KASAN_SW_TAGS
+ default 0xdffffff800000000 if ARM64_VA_BITS_36 && !KASAN_SW_TAGS
+ default 0xefff800000000000 if (ARM64_VA_BITS_48 || ARM64_VA_BITS_52) && KASAN_SW_TAGS
+ default 0xefffc00000000000 if ARM64_VA_BITS_47 && KASAN_SW_TAGS
+ default 0xeffffe0000000000 if ARM64_VA_BITS_42 && KASAN_SW_TAGS
+ default 0xefffffc000000000 if ARM64_VA_BITS_39 && KASAN_SW_TAGS
+ default 0xeffffff800000000 if ARM64_VA_BITS_36 && KASAN_SW_TAGS
default 0xffffffffffffffff
source "arch/arm64/Kconfig.platforms"
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 1ded73189874..a9bb750b3dac 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -44,7 +44,7 @@
#define _PAGE_OFFSET(va) (-(UL(1) << (va)))
#define PAGE_OFFSET (_PAGE_OFFSET(VA_BITS))
#define KIMAGE_VADDR (MODULES_END)
-#define BPF_JIT_REGION_START (KASAN_SHADOW_END)
+#define BPF_JIT_REGION_START (_PAGE_END(VA_BITS_MIN))
#define BPF_JIT_REGION_SIZE (SZ_128M)
#define BPF_JIT_REGION_END (BPF_JIT_REGION_START + BPF_JIT_REGION_SIZE)
#define MODULES_END (MODULES_VADDR + MODULES_VSIZE)
@@ -76,10 +76,11 @@
#define KASAN_SHADOW_OFFSET _AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
#define KASAN_SHADOW_END ((UL(1) << (64 - KASAN_SHADOW_SCALE_SHIFT)) \
+ KASAN_SHADOW_OFFSET)
+#define PAGE_END (KASAN_SHADOW_END - (1UL << (vabits_actual - KASAN_SHADOW_SCALE_SHIFT)))
#define KASAN_THREAD_SHIFT 1
#else
#define KASAN_THREAD_SHIFT 0
-#define KASAN_SHADOW_END (_PAGE_END(VA_BITS_MIN))
+#define PAGE_END (_PAGE_END(VA_BITS_MIN))
#endif /* CONFIG_KASAN */
#define MIN_THREAD_SHIFT (14 + KASAN_THREAD_SHIFT)
@@ -162,7 +163,6 @@
#include <asm/bug.h>
extern u64 vabits_actual;
-#define PAGE_END (_PAGE_END(vabits_actual))
extern s64 memstart_addr;
/* PHYS_OFFSET - the physical address of the start of memory. */
@@ -237,7 +237,7 @@ static inline const void *__tag_set(const void *addr, u8 tag)
* space. Testing the top bit for the start of the region is a
* sufficient check and avoids having to worry about the tag.
*/
-#define __is_lm_address(addr) (!(((u64)addr) & BIT(vabits_actual - 1)))
+#define __is_lm_address(addr) ((untagged_addr(addr) & ~PAGE_OFFSET) < (PAGE_END - PAGE_OFFSET))
#define __lm_to_phys(addr) (((addr) & ~PAGE_OFFSET) + PHYS_OFFSET)
#define __kimg_to_phys(addr) ((addr) - kimage_voffset)
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 324f0e0894f6..9090779dd3cd 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -270,7 +270,7 @@ static void __init fdt_enforce_memory_region(void)
void __init arm64_memblock_init(void)
{
- const s64 linear_region_size = BIT(vabits_actual - 1);
+ const s64 linear_region_size = PAGE_END - _PAGE_OFFSET(vabits_actual);
/* Handle linux,usable-memory-range property */
fdt_enforce_memory_region();
--
2.17.1
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