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arm64: mm: extend linear region for 52-bit VA configurations

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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@kernel.org>
Reviewed-by: Steve Capper <steve.capper@arm.com>
Link: https://lore.kernel.org/r/20201008153602.9467-3-ardb@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Ard Biesheuvel 2020-10-08 17:36:00 +02:00 committed by Catalin Marinas
parent f8394f232b
commit f4693c2716
5 changed files with 26 additions and 30 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
Documentation/arm64/kasan-offsets.sh
View File

@ -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)) ))
}

19
Documentation/arm64/memory.rst
View File

@ -32,10 +32,10 @@ AArch64 Linux memory layout with 4KB pages + 4 levels (48-bit)::
-----------------------------------------------------------------------
0000000000000000 0000ffffffffffff 256TB user
ffff000000000000 ffff7fffffffffff 128TB kernel logical memory map
ffff800000000000 ffff9fffffffffff 32TB kasan shadow region
ffffa00000000000 ffffa00007ffffff 128MB bpf jit region
ffffa00008000000 ffffa0000fffffff 128MB modules
ffffa00010000000 fffffdffbffeffff ~93TB vmalloc
[ ffff600000000000 ffff7fffffffffff ] 32TB [ kasan shadow region ]
ffff800000000000 ffff800007ffffff 128MB bpf jit region
ffff800008000000 ffff80000fffffff 128MB modules
ffff800010000000 fffffdffbffeffff 125TB vmalloc
fffffdffbfff0000 fffffdfffe5f8fff ~998MB [guard region]
fffffdfffe5f9000 fffffdfffe9fffff 4124KB fixed mappings
fffffdfffea00000 fffffdfffebfffff 2MB [guard region]
@ -50,12 +50,11 @@ AArch64 Linux memory layout with 64KB pages + 3 levels (52-bit with HW support):
Start End Size Use
-----------------------------------------------------------------------
0000000000000000 000fffffffffffff 4PB user
fff0000000000000 fff7ffffffffffff 2PB kernel logical memory map
fff8000000000000 fffd9fffffffffff 1440TB [gap]
fffda00000000000 ffff9fffffffffff 512TB kasan shadow region
ffffa00000000000 ffffa00007ffffff 128MB bpf jit region
ffffa00008000000 ffffa0000fffffff 128MB modules
ffffa00010000000 fffff81ffffeffff ~88TB vmalloc
fff0000000000000 ffff7fffffffffff ~4PB kernel logical memory map
[ fffd800000000000 ffff7fffffffffff ] 512TB [ kasan shadow region ]
ffff800000000000 ffff800007ffffff 128MB bpf jit region
ffff800008000000 ffff80000fffffff 128MB modules
ffff800010000000 fffff81ffffeffff 120TB vmalloc
fffff81fffff0000 fffffc1ffe58ffff ~3TB [guard region]
fffffc1ffe590000 fffffc1ffe9fffff 4544KB fixed mappings
fffffc1ffea00000 fffffc1ffebfffff 2MB [guard region]

20
arch/arm64/Kconfig
View File

@ -331,16 +331,16 @@ 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"

12
arch/arm64/include/asm/memory.h
View File

@ -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)
@ -167,7 +168,6 @@
#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. */
@ -238,11 +238,9 @@ static inline const void *__tag_set(const void *addr, u8 tag)
/*
* The linear kernel range starts at the bottom of the virtual address
* space. Testing the top bit for the start of the region is a
* sufficient check and avoids having to worry about the tag.
* The linear kernel range starts at the bottom of the virtual address space.
*/
#define __is_lm_address(addr) (!(((u64)addr) & BIT(vabits_actual - 1)))
#define __is_lm_address(addr) (((u64)(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)

2
arch/arm64/mm/init.c
View File

@ -269,7 +269,7 @@ 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();