On riscv, mmap currently returns an address from the largest address space that can fit entirely inside of the hint address. This makes it such that the hint address is almost never returned. This patch raises the mappable area up to and including the hint address. This allows mmap to often return the hint address, which allows a performance improvement over searching for a valid address as well as making the behavior more similar to other architectures.
Note that a previous patch introduced stronger semantics compared to other architectures for riscv mmap. On riscv, mmap will not use bits in the upper bits of the virtual address depending on the hint address. On other architectures, a random address is returned in the address space requested. On all architectures the hint address will be returned if it is available. This allows riscv applications to configure how many bits in the virtual address should be left empty. This has the two benefits of being able to request address spaces that are smaller than the default and doesn't require the application to know the page table layout of riscv.
Signed-off-by: Charlie Jenkins charlie@rivosinc.com --- Changes in v3: - Add back forgotten semi-colon - Fix test cases - Add support for rv32 - Change cover letter name so it's not the same as patch 1 - Link to v2: https://lore.kernel.org/r/20240130-use_mmap_hint_address-v2-0-f34ebfd33053@r...
Changes in v2: - Add back forgotten "mmap_end = STACK_TOP_MAX" - Link to v1: https://lore.kernel.org/r/20240129-use_mmap_hint_address-v1-0-4c74da813ba1@r...
--- Charlie Jenkins (3): riscv: mm: Use hint address in mmap if available selftests: riscv: Generalize mm selftests docs: riscv: Define behavior of mmap
Documentation/arch/riscv/vm-layout.rst | 16 ++-- arch/riscv/include/asm/processor.h | 27 +++--- tools/testing/selftests/riscv/mm/mmap_bottomup.c | 23 +---- tools/testing/selftests/riscv/mm/mmap_default.c | 23 +---- tools/testing/selftests/riscv/mm/mmap_test.h | 107 ++++++++++++++--------- 5 files changed, 83 insertions(+), 113 deletions(-) --- base-commit: 556e2d17cae620d549c5474b1ece053430cd50bc change-id: 20240119-use_mmap_hint_address-f9f4b1b6f5f1
On riscv it is guaranteed that the address returned by mmap is less than the hint address. Allow mmap to return an address all the way up to addr, if provided, rather than just up to the lower address space.
This provides a performance benefit as well, allowing mmap to exit after checking that the address is in range rather than searching for a valid address.
It is possible to provide an address that uses at most the same number of bits, however it is significantly more computationally expensive to provide that number rather than setting the max to be the hint address. There is the instruction clz/clzw in Zbb that returns the highest set bit which could be used to performantly implement this, but it would still be slower than the current implementation. At worst case, half of the address would not be able to be allocated when a hint address is provided.
Signed-off-by: Charlie Jenkins charlie@rivosinc.com --- arch/riscv/include/asm/processor.h | 27 +++++++++++---------------- 1 file changed, 11 insertions(+), 16 deletions(-)
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h index f19f861cda54..8ece7a8f0e18 100644 --- a/arch/riscv/include/asm/processor.h +++ b/arch/riscv/include/asm/processor.h @@ -14,22 +14,16 @@
#include <asm/ptrace.h>
-#ifdef CONFIG_64BIT -#define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1)) -#define STACK_TOP_MAX TASK_SIZE_64 - #define arch_get_mmap_end(addr, len, flags) \ ({ \ unsigned long mmap_end; \ typeof(addr) _addr = (addr); \ - if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) && is_compat_task())) \ + if ((_addr) == 0 || \ + (IS_ENABLED(CONFIG_COMPAT) && is_compat_task()) || \ + ((_addr + len) > BIT(VA_BITS - 1))) \ mmap_end = STACK_TOP_MAX; \ - else if ((_addr) >= VA_USER_SV57) \ - mmap_end = STACK_TOP_MAX; \ - else if ((((_addr) >= VA_USER_SV48)) && (VA_BITS >= VA_BITS_SV48)) \ - mmap_end = VA_USER_SV48; \ else \ - mmap_end = VA_USER_SV39; \ + mmap_end = (_addr + len); \ mmap_end; \ })
@@ -39,17 +33,18 @@ typeof(addr) _addr = (addr); \ typeof(base) _base = (base); \ unsigned long rnd_gap = DEFAULT_MAP_WINDOW - (_base); \ - if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) && is_compat_task())) \ + if ((_addr) == 0 || \ + (IS_ENABLED(CONFIG_COMPAT) && is_compat_task()) || \ + ((_addr + len) > BIT(VA_BITS - 1))) \ mmap_base = (_base); \ - else if (((_addr) >= VA_USER_SV57) && (VA_BITS >= VA_BITS_SV57)) \ - mmap_base = VA_USER_SV57 - rnd_gap; \ - else if ((((_addr) >= VA_USER_SV48)) && (VA_BITS >= VA_BITS_SV48)) \ - mmap_base = VA_USER_SV48 - rnd_gap; \ else \ - mmap_base = VA_USER_SV39 - rnd_gap; \ + mmap_base = (_addr + len) - rnd_gap; \ mmap_base; \ })
+#ifdef CONFIG_64BIT +#define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1)) +#define STACK_TOP_MAX TASK_SIZE_64 #else #define DEFAULT_MAP_WINDOW TASK_SIZE #define STACK_TOP_MAX TASK_SIZE
On Tue, 2024-01-30 at 17:07 -0800, Charlie Jenkins wrote:
On riscv it is guaranteed that the address returned by mmap is less than the hint address. Allow mmap to return an address all the way up to addr, if provided, rather than just up to the lower address space.
This provides a performance benefit as well, allowing mmap to exit after checking that the address is in range rather than searching for a valid address.
It is possible to provide an address that uses at most the same number of bits, however it is significantly more computationally expensive to provide that number rather than setting the max to be the hint address. There is the instruction clz/clzw in Zbb that returns the highest set bit which could be used to performantly implement this, but it would still be slower than the current implementation. At worst case, half of the address would not be able to be allocated when a hint address is provided.
Signed-off-by: Charlie Jenkins charlie@rivosinc.com
arch/riscv/include/asm/processor.h | 27 +++++++++++---------------- 1 file changed, 11 insertions(+), 16 deletions(-)
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h index f19f861cda54..8ece7a8f0e18 100644 --- a/arch/riscv/include/asm/processor.h +++ b/arch/riscv/include/asm/processor.h @@ -14,22 +14,16 @@ #include <asm/ptrace.h> -#ifdef CONFIG_64BIT -#define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1)) -#define STACK_TOP_MAX TASK_SIZE_64
#define arch_get_mmap_end(addr, len, flags) \ ({ \ unsigned long mmap_end; \ typeof(addr) _addr = (addr); \
- if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) &&
is_compat_task())) \
- if ((_addr) == 0 || \
- (IS_ENABLED(CONFIG_COMPAT) && is_compat_task()) || \
- ((_addr + len) > BIT(VA_BITS -
1))) \ mmap_end = STACK_TOP_MAX; \
- else if ((_addr) >= VA_USER_SV57) \
mmap_end = STACK_TOP_MAX; \- else if ((((_addr) >= VA_USER_SV48)) && (VA_BITS >=
VA_BITS_SV48)) \
mmap_end = VA_USER_SV48; \else \
mmap_end = VA_USER_SV39; \
mmap_end = (_addr + len); \mmap_end; \ }) @@ -39,17 +33,18 @@ typeof(addr) _addr = (addr); \ typeof(base) _base = (base); \ unsigned long rnd_gap = DEFAULT_MAP_WINDOW - (_base); \
- if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) &&
is_compat_task())) \
- if ((_addr) == 0 || \
- (IS_ENABLED(CONFIG_COMPAT) && is_compat_task()) || \
- ((_addr + len) > BIT(VA_BITS -
1))) \ mmap_base = (_base); \
- else if (((_addr) >= VA_USER_SV57) && (VA_BITS >=
VA_BITS_SV57)) \
mmap_base = VA_USER_SV57 - rnd_gap; \- else if ((((_addr) >= VA_USER_SV48)) && (VA_BITS >=
VA_BITS_SV48)) \
mmap_base = VA_USER_SV48 - rnd_gap; \else \
mmap_base = VA_USER_SV39 - rnd_gap; \
mmap_base = (_addr + len) - rnd_gap; \mmap_base; \ }) +#ifdef CONFIG_64BIT +#define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1)) +#define STACK_TOP_MAX TASK_SIZE_64 #else #define DEFAULT_MAP_WINDOW TASK_SIZE #define STACK_TOP_MAX TASK_SIZE
I have carefully tested your patch on qemu with sv57. A bug that needs to be solved is that mmap with the same hint address without MAP_FIXED set will fail the second time.
Userspace code to reproduce the bug:
#include <sys/mman.h> #include <stdio.h> #include <stdint.h>
void test(char *addr) { char *res = mmap(addr, 4096, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); printf("hint %p got %p.\n", addr, res); }
int main (void) { test(1<<30); test(1<<30); test(1<<30); return 0; }
output:
hint 0x40000000 got 0x40000000. hint 0x40000000 got 0xffffffffffffffff. hint 0x40000000 got 0xffffffffffffffff.
output on x86:
hint 0x40000000 got 0x40000000. hint 0x40000000 got 0x7f9171363000. hint 0x40000000 got 0x7f9171362000.
It may need to implement a special arch_get_unmapped_area and arch_get_unmapped_area_topdown function.
On Wed, 2024-01-31 at 22:41 +0800, Yangyu Chen wrote:
On Tue, 2024-01-30 at 17:07 -0800, Charlie Jenkins wrote:
On riscv it is guaranteed that the address returned by mmap is less than the hint address. Allow mmap to return an address all the way up to addr, if provided, rather than just up to the lower address space.
This provides a performance benefit as well, allowing mmap to exit after checking that the address is in range rather than searching for a valid address.
It is possible to provide an address that uses at most the same number of bits, however it is significantly more computationally expensive to provide that number rather than setting the max to be the hint address. There is the instruction clz/clzw in Zbb that returns the highest set bit which could be used to performantly implement this, but it would still be slower than the current implementation. At worst case, half of the address would not be able to be allocated when a hint address is provided.
Signed-off-by: Charlie Jenkins charlie@rivosinc.com
arch/riscv/include/asm/processor.h | 27 +++++++++++---------------
1 file changed, 11 insertions(+), 16 deletions(-)
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h index f19f861cda54..8ece7a8f0e18 100644 --- a/arch/riscv/include/asm/processor.h +++ b/arch/riscv/include/asm/processor.h @@ -14,22 +14,16 @@ #include <asm/ptrace.h> -#ifdef CONFIG_64BIT -#define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1)) -#define STACK_TOP_MAX TASK_SIZE_64
#define arch_get_mmap_end(addr, len, flags) \ ({ \ unsigned long mmap_end; \ typeof(addr) _addr = (addr); \
- if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) &&
is_compat_task())) \
- if ((_addr) == 0 || \
- (IS_ENABLED(CONFIG_COMPAT) && is_compat_task()) || \
- ((_addr + len) > BIT(VA_BITS -
1))) \ mmap_end = STACK_TOP_MAX; \
- else if ((_addr) >= VA_USER_SV57) \
mmap_end = STACK_TOP_MAX; \- else if ((((_addr) >= VA_USER_SV48)) && (VA_BITS >=
VA_BITS_SV48)) \
mmap_end = VA_USER_SV48; \else \
mmap_end = VA_USER_SV39; \
mmap_end = (_addr + len); \mmap_end; \ }) @@ -39,17 +33,18 @@ typeof(addr) _addr = (addr); \ typeof(base) _base = (base); \ unsigned long rnd_gap = DEFAULT_MAP_WINDOW - (_base); \
- if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) &&
is_compat_task())) \
- if ((_addr) == 0 || \
- (IS_ENABLED(CONFIG_COMPAT) && is_compat_task()) || \
- ((_addr + len) > BIT(VA_BITS -
1))) \ mmap_base = (_base); \
- else if (((_addr) >= VA_USER_SV57) && (VA_BITS >=
VA_BITS_SV57)) \
mmap_base = VA_USER_SV57 - rnd_gap; \- else if ((((_addr) >= VA_USER_SV48)) && (VA_BITS >=
VA_BITS_SV48)) \
mmap_base = VA_USER_SV48 - rnd_gap; \else \
mmap_base = VA_USER_SV39 - rnd_gap; \
mmap_base = (_addr + len) - rnd_gap; \mmap_base; \ }) +#ifdef CONFIG_64BIT +#define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1)) +#define STACK_TOP_MAX TASK_SIZE_64 #else #define DEFAULT_MAP_WINDOW TASK_SIZE #define STACK_TOP_MAX TASK_SIZE
I have carefully tested your patch on qemu with sv57. A bug that needs to be solved is that mmap with the same hint address without MAP_FIXED set will fail the second time.
Userspace code to reproduce the bug:
#include <sys/mman.h> #include <stdio.h> #include <stdint.h>
void test(char *addr) { char *res = mmap(addr, 4096, PROT_READ | PROT_WRITE, MAP_ANONYMOUS
MAP_PRIVATE, -1, 0);
printf("hint %p got %p.\n", addr, res); }
int main (void) { test(1<<30); test(1<<30); test(1<<30); return 0; }
output:
hint 0x40000000 got 0x40000000. hint 0x40000000 got 0xffffffffffffffff. hint 0x40000000 got 0xffffffffffffffff.
output on x86:
hint 0x40000000 got 0x40000000. hint 0x40000000 got 0x7f9171363000. hint 0x40000000 got 0x7f9171362000.
It may need to implement a special arch_get_unmapped_area and arch_get_unmapped_area_topdown function.
This is because hint address < rnd_gap. I have tried to let mmap_base = min((_addr + len), (base) + TASK_SIZE - DEFAULT_MAP_WINDOW). However it does not work for bottom-up while ulimit -s is unlimited. You said this behavior is expected from patch v2 review. However it brings a new regression even on sv39 systems.
I still don't know the reason why use addr+len as the upper-bound. I think solution like x86/arm64/powerpc provide two address space switch based on whether hint address above the default map window is enough.
On Wed, Jan 31, 2024 at 11:59:43PM +0800, Yangyu Chen wrote:
On Wed, 2024-01-31 at 22:41 +0800, Yangyu Chen wrote:
On Tue, 2024-01-30 at 17:07 -0800, Charlie Jenkins wrote:
On riscv it is guaranteed that the address returned by mmap is less than the hint address. Allow mmap to return an address all the way up to addr, if provided, rather than just up to the lower address space.
This provides a performance benefit as well, allowing mmap to exit after checking that the address is in range rather than searching for a valid address.
It is possible to provide an address that uses at most the same number of bits, however it is significantly more computationally expensive to provide that number rather than setting the max to be the hint address. There is the instruction clz/clzw in Zbb that returns the highest set bit which could be used to performantly implement this, but it would still be slower than the current implementation. At worst case, half of the address would not be able to be allocated when a hint address is provided.
Signed-off-by: Charlie Jenkins charlie@rivosinc.com
arch/riscv/include/asm/processor.h | 27 +++++++++++---------------
1 file changed, 11 insertions(+), 16 deletions(-)
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h index f19f861cda54..8ece7a8f0e18 100644 --- a/arch/riscv/include/asm/processor.h +++ b/arch/riscv/include/asm/processor.h @@ -14,22 +14,16 @@ #include <asm/ptrace.h> -#ifdef CONFIG_64BIT -#define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1)) -#define STACK_TOP_MAX TASK_SIZE_64
#define arch_get_mmap_end(addr, len, flags) \ ({ \ unsigned long mmap_end; \ typeof(addr) _addr = (addr); \
- if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) &&
is_compat_task())) \
- if ((_addr) == 0 || \
- (IS_ENABLED(CONFIG_COMPAT) && is_compat_task()) || \
- ((_addr + len) > BIT(VA_BITS -
1))) \ mmap_end = STACK_TOP_MAX; \
- else if ((_addr) >= VA_USER_SV57) \
mmap_end = STACK_TOP_MAX; \- else if ((((_addr) >= VA_USER_SV48)) && (VA_BITS >=
VA_BITS_SV48)) \
mmap_end = VA_USER_SV48; \else \
mmap_end = VA_USER_SV39; \
mmap_end = (_addr + len); \mmap_end; \ }) @@ -39,17 +33,18 @@ typeof(addr) _addr = (addr); \ typeof(base) _base = (base); \ unsigned long rnd_gap = DEFAULT_MAP_WINDOW - (_base); \
- if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) &&
is_compat_task())) \
- if ((_addr) == 0 || \
- (IS_ENABLED(CONFIG_COMPAT) && is_compat_task()) || \
- ((_addr + len) > BIT(VA_BITS -
1))) \ mmap_base = (_base); \
- else if (((_addr) >= VA_USER_SV57) && (VA_BITS >=
VA_BITS_SV57)) \
mmap_base = VA_USER_SV57 - rnd_gap; \- else if ((((_addr) >= VA_USER_SV48)) && (VA_BITS >=
VA_BITS_SV48)) \
mmap_base = VA_USER_SV48 - rnd_gap; \else \
mmap_base = VA_USER_SV39 - rnd_gap; \
mmap_base = (_addr + len) - rnd_gap; \mmap_base; \ }) +#ifdef CONFIG_64BIT +#define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1)) +#define STACK_TOP_MAX TASK_SIZE_64 #else #define DEFAULT_MAP_WINDOW TASK_SIZE #define STACK_TOP_MAX TASK_SIZE
I have carefully tested your patch on qemu with sv57. A bug that needs to be solved is that mmap with the same hint address without MAP_FIXED set will fail the second time.
Userspace code to reproduce the bug:
#include <sys/mman.h> #include <stdio.h> #include <stdint.h>
void test(char *addr) { char *res = mmap(addr, 4096, PROT_READ | PROT_WRITE, MAP_ANONYMOUS
MAP_PRIVATE, -1, 0);
printf("hint %p got %p.\n", addr, res); }
int main (void) { test(1<<30); test(1<<30); test(1<<30); return 0; }
output:
hint 0x40000000 got 0x40000000. hint 0x40000000 got 0xffffffffffffffff. hint 0x40000000 got 0xffffffffffffffff.
output on x86:
hint 0x40000000 got 0x40000000. hint 0x40000000 got 0x7f9171363000. hint 0x40000000 got 0x7f9171362000.
It may need to implement a special arch_get_unmapped_area and arch_get_unmapped_area_topdown function.
This is because hint address < rnd_gap. I have tried to let mmap_base = min((_addr + len), (base) + TASK_SIZE - DEFAULT_MAP_WINDOW). However it does not work for bottom-up while ulimit -s is unlimited. You said this behavior is expected from patch v2 review. However it brings a new regression even on sv39 systems.
I still don't know the reason why use addr+len as the upper-bound. I think solution like x86/arm64/powerpc provide two address space switch based on whether hint address above the default map window is enough.
Yep this is expected. It is up to the maintainers to decide.
- Charlie
On Thu, 01 Feb 2024 18:28:06 PST (-0800), Charlie Jenkins wrote:
On Wed, Jan 31, 2024 at 11:59:43PM +0800, Yangyu Chen wrote:
On Wed, 2024-01-31 at 22:41 +0800, Yangyu Chen wrote:
On Tue, 2024-01-30 at 17:07 -0800, Charlie Jenkins wrote:
On riscv it is guaranteed that the address returned by mmap is less than the hint address. Allow mmap to return an address all the way up to addr, if provided, rather than just up to the lower address space.
This provides a performance benefit as well, allowing mmap to exit after checking that the address is in range rather than searching for a valid address.
It is possible to provide an address that uses at most the same number of bits, however it is significantly more computationally expensive to provide that number rather than setting the max to be the hint address. There is the instruction clz/clzw in Zbb that returns the highest set bit which could be used to performantly implement this, but it would still be slower than the current implementation. At worst case, half of the address would not be able to be allocated when a hint address is provided.
Signed-off-by: Charlie Jenkins charlie@rivosinc.com
arch/riscv/include/asm/processor.h | 27 +++++++++++---------------
1 file changed, 11 insertions(+), 16 deletions(-)
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h index f19f861cda54..8ece7a8f0e18 100644 --- a/arch/riscv/include/asm/processor.h +++ b/arch/riscv/include/asm/processor.h @@ -14,22 +14,16 @@ #include <asm/ptrace.h> -#ifdef CONFIG_64BIT -#define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1)) -#define STACK_TOP_MAX TASK_SIZE_64
#define arch_get_mmap_end(addr, len, flags) \ ({ \ unsigned long mmap_end; \ typeof(addr) _addr = (addr); \
- if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) &&
is_compat_task())) \
- if ((_addr) == 0 || \
- (IS_ENABLED(CONFIG_COMPAT) && is_compat_task()) || \
- ((_addr + len) > BIT(VA_BITS -
1))) \ mmap_end = STACK_TOP_MAX; \
- else if ((_addr) >= VA_USER_SV57) \
mmap_end = STACK_TOP_MAX; \- else if ((((_addr) >= VA_USER_SV48)) && (VA_BITS >=
VA_BITS_SV48)) \
mmap_end = VA_USER_SV48; \else \
mmap_end = VA_USER_SV39; \
mmap_end = (_addr + len); \mmap_end; \ }) @@ -39,17 +33,18 @@ typeof(addr) _addr = (addr); \ typeof(base) _base = (base); \ unsigned long rnd_gap = DEFAULT_MAP_WINDOW - (_base); \
- if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) &&
is_compat_task())) \
- if ((_addr) == 0 || \
- (IS_ENABLED(CONFIG_COMPAT) && is_compat_task()) || \
- ((_addr + len) > BIT(VA_BITS -
1))) \ mmap_base = (_base); \
- else if (((_addr) >= VA_USER_SV57) && (VA_BITS >=
VA_BITS_SV57)) \
mmap_base = VA_USER_SV57 - rnd_gap; \- else if ((((_addr) >= VA_USER_SV48)) && (VA_BITS >=
VA_BITS_SV48)) \
mmap_base = VA_USER_SV48 - rnd_gap; \else \
mmap_base = VA_USER_SV39 - rnd_gap; \
mmap_base = (_addr + len) - rnd_gap; \mmap_base; \ }) +#ifdef CONFIG_64BIT +#define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1)) +#define STACK_TOP_MAX TASK_SIZE_64 #else #define DEFAULT_MAP_WINDOW TASK_SIZE #define STACK_TOP_MAX TASK_SIZE
I have carefully tested your patch on qemu with sv57. A bug that needs to be solved is that mmap with the same hint address without MAP_FIXED set will fail the second time.
Userspace code to reproduce the bug:
#include <sys/mman.h> #include <stdio.h> #include <stdint.h>
void test(char *addr) { char *res = mmap(addr, 4096, PROT_READ | PROT_WRITE, MAP_ANONYMOUS
MAP_PRIVATE, -1, 0);
printf("hint %p got %p.\n", addr, res); }
int main (void) { test(1<<30); test(1<<30); test(1<<30); return 0; }
output:
hint 0x40000000 got 0x40000000. hint 0x40000000 got 0xffffffffffffffff. hint 0x40000000 got 0xffffffffffffffff.
output on x86:
hint 0x40000000 got 0x40000000. hint 0x40000000 got 0x7f9171363000. hint 0x40000000 got 0x7f9171362000.
It may need to implement a special arch_get_unmapped_area and arch_get_unmapped_area_topdown function.
This is because hint address < rnd_gap. I have tried to let mmap_base = min((_addr + len), (base) + TASK_SIZE - DEFAULT_MAP_WINDOW). However it does not work for bottom-up while ulimit -s is unlimited. You said this behavior is expected from patch v2 review. However it brings a new regression even on sv39 systems.
I still don't know the reason why use addr+len as the upper-bound. I think solution like x86/arm64/powerpc provide two address space switch based on whether hint address above the default map window is enough.
Yep this is expected. It is up to the maintainers to decide.
Sorry I forgot to reply to this, I had a buffer sitting around somewhere but I must have lost it.
I think Charlie's approach is the right way to go. Putting my userspace hat on, I'd much rather have my allocations fail rather than silently ignore the hint when there's memory pressure.
If there's some real use case that needs these low hints to be silently ignored under VA pressure then we can try and figure something out that makes those applications work.
- Charlie
The behavior of mmap on riscv is defined to not provide an address that uses more bits than the hint address, if provided. Make the tests reflect that.
Signed-off-by: Charlie Jenkins charlie@rivosinc.com --- tools/testing/selftests/riscv/mm/mmap_bottomup.c | 23 +---- tools/testing/selftests/riscv/mm/mmap_default.c | 23 +---- tools/testing/selftests/riscv/mm/mmap_test.h | 107 ++++++++++++++--------- 3 files changed, 67 insertions(+), 86 deletions(-)
diff --git a/tools/testing/selftests/riscv/mm/mmap_bottomup.c b/tools/testing/selftests/riscv/mm/mmap_bottomup.c index 1757d19ca89b..7f7d3eb8b9c9 100644 --- a/tools/testing/selftests/riscv/mm/mmap_bottomup.c +++ b/tools/testing/selftests/riscv/mm/mmap_bottomup.c @@ -6,30 +6,9 @@
TEST(infinite_rlimit) { -// Only works on 64 bit -#if __riscv_xlen == 64 - struct addresses mmap_addresses; - EXPECT_EQ(BOTTOM_UP, memory_layout());
- do_mmaps(&mmap_addresses); - - EXPECT_NE(MAP_FAILED, mmap_addresses.no_hint); - EXPECT_NE(MAP_FAILED, mmap_addresses.on_37_addr); - EXPECT_NE(MAP_FAILED, mmap_addresses.on_38_addr); - EXPECT_NE(MAP_FAILED, mmap_addresses.on_46_addr); - EXPECT_NE(MAP_FAILED, mmap_addresses.on_47_addr); - EXPECT_NE(MAP_FAILED, mmap_addresses.on_55_addr); - EXPECT_NE(MAP_FAILED, mmap_addresses.on_56_addr); - - EXPECT_GT(1UL << 47, (unsigned long)mmap_addresses.no_hint); - EXPECT_GT(1UL << 38, (unsigned long)mmap_addresses.on_37_addr); - EXPECT_GT(1UL << 38, (unsigned long)mmap_addresses.on_38_addr); - EXPECT_GT(1UL << 38, (unsigned long)mmap_addresses.on_46_addr); - EXPECT_GT(1UL << 47, (unsigned long)mmap_addresses.on_47_addr); - EXPECT_GT(1UL << 47, (unsigned long)mmap_addresses.on_55_addr); - EXPECT_GT(1UL << 56, (unsigned long)mmap_addresses.on_56_addr); -#endif + TEST_MMAPS; }
TEST_HARNESS_MAIN diff --git a/tools/testing/selftests/riscv/mm/mmap_default.c b/tools/testing/selftests/riscv/mm/mmap_default.c index c63c60b9397e..2ba3ec990006 100644 --- a/tools/testing/selftests/riscv/mm/mmap_default.c +++ b/tools/testing/selftests/riscv/mm/mmap_default.c @@ -6,30 +6,9 @@
TEST(default_rlimit) { -// Only works on 64 bit -#if __riscv_xlen == 64 - struct addresses mmap_addresses; - EXPECT_EQ(TOP_DOWN, memory_layout());
- do_mmaps(&mmap_addresses); - - EXPECT_NE(MAP_FAILED, mmap_addresses.no_hint); - EXPECT_NE(MAP_FAILED, mmap_addresses.on_37_addr); - EXPECT_NE(MAP_FAILED, mmap_addresses.on_38_addr); - EXPECT_NE(MAP_FAILED, mmap_addresses.on_46_addr); - EXPECT_NE(MAP_FAILED, mmap_addresses.on_47_addr); - EXPECT_NE(MAP_FAILED, mmap_addresses.on_55_addr); - EXPECT_NE(MAP_FAILED, mmap_addresses.on_56_addr); - - EXPECT_GT(1UL << 47, (unsigned long)mmap_addresses.no_hint); - EXPECT_GT(1UL << 38, (unsigned long)mmap_addresses.on_37_addr); - EXPECT_GT(1UL << 38, (unsigned long)mmap_addresses.on_38_addr); - EXPECT_GT(1UL << 38, (unsigned long)mmap_addresses.on_46_addr); - EXPECT_GT(1UL << 47, (unsigned long)mmap_addresses.on_47_addr); - EXPECT_GT(1UL << 47, (unsigned long)mmap_addresses.on_55_addr); - EXPECT_GT(1UL << 56, (unsigned long)mmap_addresses.on_56_addr); -#endif + TEST_MMAPS; }
TEST_HARNESS_MAIN diff --git a/tools/testing/selftests/riscv/mm/mmap_test.h b/tools/testing/selftests/riscv/mm/mmap_test.h index 9b8434f62f57..36e78d991d5e 100644 --- a/tools/testing/selftests/riscv/mm/mmap_test.h +++ b/tools/testing/selftests/riscv/mm/mmap_test.h @@ -4,60 +4,83 @@ #include <sys/mman.h> #include <sys/resource.h> #include <stddef.h> +#include <strings.h> +#include "../../kselftest_harness.h"
#define TOP_DOWN 0 #define BOTTOM_UP 1
-struct addresses { - int *no_hint; - int *on_37_addr; - int *on_38_addr; - int *on_46_addr; - int *on_47_addr; - int *on_55_addr; - int *on_56_addr; +#if __riscv_xlen == 64 +uint64_t random_addresses[] = { + 0x19764f0d73b3a9f0, 0x016049584cecef59, 0x3580bdd3562f4acd, + 0x1164219f20b17da0, 0x07d97fcb40ff2373, 0x76ec528921272ee7, + 0x4dd48c38a3de3f70, 0x2e11415055f6997d, 0x14b43334ac476c02, + 0x375a60795aff19f6, 0x47f3051725b8ee1a, 0x4e697cf240494a9f, + 0x456b59b5c2f9e9d1, 0x101724379d63cb96, 0x7fe9ad31619528c1, + 0x2f417247c495c2ea, 0x329a5a5b82943a5e, 0x06d7a9d6adcd3827, + 0x327b0b9ee37f62d5, 0x17c7b1851dfd9b76, 0x006ebb6456ec2cd9, + 0x00836cd14146a134, 0x00e5c4dcde7126db, 0x004c29feadf75753, + 0x00d8b20149ed930c, 0x00d71574c269387a, 0x0006ebe4a82acb7a, + 0x0016135df51f471b, 0x00758bdb55455160, 0x00d0bdd949b13b32, + 0x00ecea01e7c5f54b, 0x00e37b071b9948b1, 0x0011fdd00ff57ab3, + 0x00e407294b52f5ea, 0x00567748c200ed20, 0x000d073084651046, + 0x00ac896f4365463c, 0x00eb0d49a0b26216, 0x0066a2564a982a31, + 0x002e0d20237784ae, 0x0000554ff8a77a76, 0x00006ce07a54c012, + 0x000009570516d799, 0x00000954ca15b84d, 0x0000684f0d453379, + 0x00002ae5816302b5, 0x0000042403fb54bf, 0x00004bad7392bf30, + 0x00003e73bfa4b5e3, 0x00005442c29978e0, 0x00002803f11286b6, + 0x000073875d745fc6, 0x00007cede9cb8240, 0x000027df84cc6a4f, + 0x00006d7e0e74242a, 0x00004afd0b836e02, 0x000047d0e837cd82, + 0x00003b42405efeda, 0x00001531bafa4c95, 0x00007172cae34ac4, }; +#else +uint32_t random_addresses[] = { + 0x8dc302e0, 0x929ab1e0, 0xb47683ba, 0xea519c73, 0xa19f1c90, 0xc49ba213, + 0x8f57c625, 0xadfe5137, 0x874d4d95, 0xaa20f09d, 0xcf21ebfc, 0xda7737f1, + 0xcedf392a, 0x83026c14, 0xccedca52, 0xc6ccf826, 0xe0cd9415, 0x997472ca, + 0xa21a44c1, 0xe82196f5, 0xa23fd66b, 0xc28d5590, 0xd009cdce, 0xcf0be646, + 0x8fc8c7ff, 0xe2a85984, 0xa3d3236b, 0x89a0619d, 0xc03db924, 0xb5d4cc1b, + 0xb96ee04c, 0xd191da48, 0xb432a000, 0xaa2bebbc, 0xa2fcb289, 0xb0cca89b, + 0xb0c18d6a, 0x88f58deb, 0xa4d42d1c, 0xe4d74e86, 0x99902b09, 0x8f786d31, + 0xbec5e381, 0x9a727e65, 0xa9a65040, 0xa880d789, 0x8f1b335e, 0xfc821c1e, + 0x97e34be4, 0xbbef84ed, 0xf447d197, 0xfd7ceee2, 0xe632348d, 0xee4590f4, + 0x958992a5, 0xd57e05d6, 0xfd240970, 0xc5b0dcff, 0xd96da2c2, 0xa7ae041d, +}; +#endif
-static inline void do_mmaps(struct addresses *mmap_addresses) -{ - /* - * Place all of the hint addresses on the boundaries of mmap - * sv39, sv48, sv57 - * User addresses end at 1<<38, 1<<47, 1<<56 respectively - */ - void *on_37_bits = (void *)(1UL << 37); - void *on_38_bits = (void *)(1UL << 38); - void *on_46_bits = (void *)(1UL << 46); - void *on_47_bits = (void *)(1UL << 47); - void *on_55_bits = (void *)(1UL << 55); - void *on_56_bits = (void *)(1UL << 56); +#define PROT (PROT_READ | PROT_WRITE) +#define FLAGS (MAP_PRIVATE | MAP_ANONYMOUS)
- int prot = PROT_READ | PROT_WRITE; - int flags = MAP_PRIVATE | MAP_ANONYMOUS; +/* mmap must return a value that doesn't use more bits than the hint address. */ +static inline unsigned long get_max_value(unsigned long input) +{ + unsigned long max_bit = (1UL << (((sizeof(unsigned long) * 8) - 1 - + __builtin_clzl(input))));
- mmap_addresses->no_hint = - mmap(NULL, 5 * sizeof(int), prot, flags, 0, 0); - mmap_addresses->on_37_addr = - mmap(on_37_bits, 5 * sizeof(int), prot, flags, 0, 0); - mmap_addresses->on_38_addr = - mmap(on_38_bits, 5 * sizeof(int), prot, flags, 0, 0); - mmap_addresses->on_46_addr = - mmap(on_46_bits, 5 * sizeof(int), prot, flags, 0, 0); - mmap_addresses->on_47_addr = - mmap(on_47_bits, 5 * sizeof(int), prot, flags, 0, 0); - mmap_addresses->on_55_addr = - mmap(on_55_bits, 5 * sizeof(int), prot, flags, 0, 0); - mmap_addresses->on_56_addr = - mmap(on_56_bits, 5 * sizeof(int), prot, flags, 0, 0); + return max_bit + (max_bit - 1); }
+#define TEST_MMAPS \ + ({ \ + void *mmap_addr; \ + for (int i = 0; i < ARRAY_SIZE(random_addresses); i++) { \ + mmap_addr = mmap((void *)random_addresses[i], \ + 5 * sizeof(int), PROT, FLAGS, 0, 0); \ + EXPECT_NE(MAP_FAILED, mmap_addr); \ + EXPECT_GE((void *)get_max_value(random_addresses[i]), \ + mmap_addr); \ + mmap_addr = mmap((void *)random_addresses[i], \ + 5 * sizeof(int), PROT, FLAGS, 0, 0); \ + EXPECT_NE(MAP_FAILED, mmap_addr); \ + EXPECT_GE((void *)get_max_value(random_addresses[i]), \ + mmap_addr); \ + } \ + }) + static inline int memory_layout(void) { - int prot = PROT_READ | PROT_WRITE; - int flags = MAP_PRIVATE | MAP_ANONYMOUS; - - void *value1 = mmap(NULL, sizeof(int), prot, flags, 0, 0); - void *value2 = mmap(NULL, sizeof(int), prot, flags, 0, 0); + void *value1 = mmap(NULL, sizeof(int), PROT, FLAGS, 0, 0); + void *value2 = mmap(NULL, sizeof(int), PROT, FLAGS, 0, 0);
return value2 > value1; }
Define mmap on riscv to not provide an address that uses more bits than the hint address, if provided.
Signed-off-by: Charlie Jenkins charlie@rivosinc.com --- Documentation/arch/riscv/vm-layout.rst | 16 +++++----------- 1 file changed, 5 insertions(+), 11 deletions(-)
diff --git a/Documentation/arch/riscv/vm-layout.rst b/Documentation/arch/riscv/vm-layout.rst index 69ff6da1dbf8..e476b4386bd9 100644 --- a/Documentation/arch/riscv/vm-layout.rst +++ b/Documentation/arch/riscv/vm-layout.rst @@ -144,14 +144,8 @@ passing 0 into the hint address parameter of mmap. On CPUs with an address space smaller than sv48, the CPU maximum supported address space will be the default.
Software can "opt-in" to receiving VAs from another VA space by providing -a hint address to mmap. A hint address passed to mmap will cause the largest -address space that fits entirely into the hint to be used, unless there is no -space left in the address space. If there is no space available in the requested -address space, an address in the next smallest available address space will be -returned. - -For example, in order to obtain 48-bit VA space, a hint address greater than -:code:`1 << 47` must be provided. Note that this is 47 due to sv48 userspace -ending at :code:`1 << 47` and the addresses beyond this are reserved for the -kernel. Similarly, to obtain 57-bit VA space addresses, a hint address greater -than or equal to :code:`1 << 56` must be provided. +a hint address to mmap. When a hint address is passed to mmap, the returned +address will never use more bits than the hint address. For example, if a hint +address of `1 << 40` is passed to mmap, a valid returned address will never use +bits 41 through 63. If no mappable addresses are available in that range, mmap +will return `MAP_FAILED`.
Hello:
This series was applied to riscv/linux.git (for-next) by Palmer Dabbelt palmer@rivosinc.com:
On Tue, 30 Jan 2024 17:06:59 -0800 you wrote:
On riscv, mmap currently returns an address from the largest address space that can fit entirely inside of the hint address. This makes it such that the hint address is almost never returned. This patch raises the mappable area up to and including the hint address. This allows mmap to often return the hint address, which allows a performance improvement over searching for a valid address as well as making the behavior more similar to other architectures.
[...]
Here is the summary with links: - [v3,1/3] riscv: mm: Use hint address in mmap if available https://git.kernel.org/riscv/c/b5b4287accd7 - [v3,2/3] selftests: riscv: Generalize mm selftests https://git.kernel.org/riscv/c/73d05262a2ca - [v3,3/3] docs: riscv: Define behavior of mmap https://git.kernel.org/riscv/c/371a3c2055db
You are awesome, thank you!
linux-kselftest-mirror@lists.linaro.org
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Charlie Jenkins -
Palmer Dabbelt -
patchwork-bot+linux-riscv＠kernel.org -
Yangyu Chen