[PATCH v1 0/5] riscv: Introduce compat-mode helpers & improve arch_get_mmap_end()

[PATCH v1 0/5] riscv: Introduce compat-mode helpers & improve arch_get_mmap_end()

[Leonardo Bras]

I just saw the opportunity of optimizing the helper is_compat_task() by
introducing a compile-time test, and it made possible to remove some
#ifdef's without any loss of performance.

I also saw the possibility of removing the direct check of task flags from
general code, and concentrated it in asm/compat.h by creating a few more
helpers, which in the end helped optimize code.

arch_get_mmap_end() just got a simple improvement and some extra docs.

Changes since RFC:
- Fused with other patchset:  Improve arch_get_mmap_end() macro
- Renamed from "Introduce & Optimize compat-mode helpers"

Leonardo Bras (5):
  riscv: Improve arch_get_mmap_end() macro
  riscv: Replace direct thread flag check with is_compat_task()
  riscv: add compile-time test into is_compat_task()
  riscv: Introduce is_compat_thread() into compat.h
  riscv: Introduce set_compat_task() in asm/compat.h

 arch/riscv/include/asm/compat.h    | 19 +++++++++++++++++++
 arch/riscv/include/asm/elf.h       | 11 ++---------
 arch/riscv/include/asm/pgtable.h   |  8 +-------
 arch/riscv/include/asm/processor.h | 16 +++++++++++-----
 arch/riscv/kernel/ptrace.c         |  6 +++---
 5 files changed, 36 insertions(+), 24 deletions(-)


base-commit: 610a9b8f49fbcf1100716370d3b5f6f884a2835a
-- 
2.43.0

[PATCH v1 1/5] riscv: Improve arch_get_mmap_end() macro

[Leonardo Bras]

This macro caused me some confusion, which took some reviewer's time to
make it clear, so I propose adding a short comment in code to avoid
confusion in the future.

Also, added some improvements to the macro, such as removing the
assumption of VA_USER_SV57 being the largest address space.

Signed-off-by: Leonardo Bras <leobras@redhat.com>
Reviewed-by: Guo Ren <guoren@kernel.org>
---
 arch/riscv/include/asm/processor.h | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
index f19f861cda549..2278e2a8362af 100644
--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -18,15 +18,21 @@
 #define DEFAULT_MAP_WINDOW	(UL(1) << (MMAP_VA_BITS - 1))
 #define STACK_TOP_MAX		TASK_SIZE_64
 
+/*
+ * addr is a hint to the maximum userspace address that mmap should provide, so
+ * this macro needs to return the largest address space available so that
+ * mmap_end < addr, being mmap_end the top of that address space.
+ * See Documentation/arch/riscv/vm-layout.rst for more details.
+ */
 #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())) \
 		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)) \
+	else if (((_addr) >= VA_USER_SV57) && (VA_BITS >= VA_BITS_SV57)) \
+		mmap_end = VA_USER_SV57;			\
+	else if (((_addr) >= VA_USER_SV48) && (VA_BITS >= VA_BITS_SV48)) \
 		mmap_end = VA_USER_SV48;			\
 	else							\
 		mmap_end = VA_USER_SV39;			\
-- 
2.43.0

[PATCH v1 2/5] riscv: Replace direct thread flag check with is_compat_task()

[Leonardo Bras]

There is some code that detects compat mode into a task by checking the
flag directly, and other code that check using the helper is_compat_task().

Since the helper already exists, use it instead of checking the flags
directly.

Signed-off-by: Leonardo Bras <leobras@redhat.com>
---
 arch/riscv/include/asm/elf.h     | 2 +-
 arch/riscv/include/asm/pgtable.h | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/include/asm/elf.h b/arch/riscv/include/asm/elf.h
index 06c236bfab53b..59a08367fddd7 100644
--- a/arch/riscv/include/asm/elf.h
+++ b/arch/riscv/include/asm/elf.h
@@ -54,7 +54,7 @@ extern bool compat_elf_check_arch(Elf32_Ehdr *hdr);
 
 #ifdef CONFIG_64BIT
 #ifdef CONFIG_COMPAT
-#define STACK_RND_MASK		(test_thread_flag(TIF_32BIT) ? \
+#define STACK_RND_MASK		(is_compat_task() ? \
 				 0x7ff >> (PAGE_SHIFT - 12) : \
 				 0x3ffff >> (PAGE_SHIFT - 12))
 #else
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index ab00235b018f8..1d472b31e0cfe 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -882,7 +882,7 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
 
 #ifdef CONFIG_COMPAT
 #define TASK_SIZE_32	(_AC(0x80000000, UL) - PAGE_SIZE)
-#define TASK_SIZE	(test_thread_flag(TIF_32BIT) ? \
+#define TASK_SIZE	(is_compat_task() ? \
 			 TASK_SIZE_32 : TASK_SIZE_64)
 #else
 #define TASK_SIZE	TASK_SIZE_64
-- 
2.43.0

[PATCH v1 3/5] riscv: add compile-time test into is_compat_task()

[Leonardo Bras]

Currently several places will test for CONFIG_COMPAT before testing
is_compat_task(), probably in order to avoid a run-time test into the task
structure.

Since is_compat_task() is an inlined function, it would be helpful to add a
compile-time test of CONFIG_COMPAT, making sure it always returns zero when
the option is not enabled during the kernel build.

With this, the compiler is able to understand in build-time that
is_compat_task() will always return 0, and optimize-out some of the extra
code introduced by the option.

This will also allow removing a lot #ifdefs that were introduced, and make
the code more clean.

Signed-off-by: Leonardo Bras <leobras@redhat.com>
Reviewed-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Andy Chiu <andy.chiu@sifive.com>
---
 arch/riscv/include/asm/compat.h    | 3 +++
 arch/riscv/include/asm/elf.h       | 4 ----
 arch/riscv/include/asm/pgtable.h   | 6 ------
 arch/riscv/include/asm/processor.h | 4 ++--
 4 files changed, 5 insertions(+), 12 deletions(-)

diff --git a/arch/riscv/include/asm/compat.h b/arch/riscv/include/asm/compat.h
index 2ac955b51148f..91517b51b8e27 100644
--- a/arch/riscv/include/asm/compat.h
+++ b/arch/riscv/include/asm/compat.h
@@ -14,6 +14,9 @@
 
 static inline int is_compat_task(void)
 {
+	if (!IS_ENABLED(CONFIG_COMPAT))
+		return 0;
+
 	return test_thread_flag(TIF_32BIT);
 }
 
diff --git a/arch/riscv/include/asm/elf.h b/arch/riscv/include/asm/elf.h
index 59a08367fddd7..2e88257cafaea 100644
--- a/arch/riscv/include/asm/elf.h
+++ b/arch/riscv/include/asm/elf.h
@@ -53,13 +53,9 @@ extern bool compat_elf_check_arch(Elf32_Ehdr *hdr);
 #define ELF_ET_DYN_BASE		((DEFAULT_MAP_WINDOW / 3) * 2)
 
 #ifdef CONFIG_64BIT
-#ifdef CONFIG_COMPAT
 #define STACK_RND_MASK		(is_compat_task() ? \
 				 0x7ff >> (PAGE_SHIFT - 12) : \
 				 0x3ffff >> (PAGE_SHIFT - 12))
-#else
-#define STACK_RND_MASK		(0x3ffff >> (PAGE_SHIFT - 12))
-#endif
 #endif
 
 /*
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index 1d472b31e0cfe..ea5b269be223a 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -127,16 +127,10 @@
 #define VA_USER_SV48 (UL(1) << (VA_BITS_SV48 - 1))
 #define VA_USER_SV57 (UL(1) << (VA_BITS_SV57 - 1))
 
-#ifdef CONFIG_COMPAT
 #define MMAP_VA_BITS_64 ((VA_BITS >= VA_BITS_SV48) ? VA_BITS_SV48 : VA_BITS)
 #define MMAP_MIN_VA_BITS_64 (VA_BITS_SV39)
 #define MMAP_VA_BITS (is_compat_task() ? VA_BITS_SV32 : MMAP_VA_BITS_64)
 #define MMAP_MIN_VA_BITS (is_compat_task() ? VA_BITS_SV32 : MMAP_MIN_VA_BITS_64)
-#else
-#define MMAP_VA_BITS ((VA_BITS >= VA_BITS_SV48) ? VA_BITS_SV48 : VA_BITS)
-#define MMAP_MIN_VA_BITS (VA_BITS_SV39)
-#endif /* CONFIG_COMPAT */
-
 #else
 #include <asm/pgtable-32.h>
 #endif /* CONFIG_64BIT */
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
index 2278e2a8362af..d2d7ce30baf3e 100644
--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -28,7 +28,7 @@
 ({								\
 	unsigned long mmap_end;					\
 	typeof(addr) _addr = (addr);				\
-	if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) && is_compat_task())) \
+	if ((_addr) == 0 || is_compat_task())			\
 		mmap_end = STACK_TOP_MAX;			\
 	else if (((_addr) >= VA_USER_SV57) && (VA_BITS >= VA_BITS_SV57)) \
 		mmap_end = VA_USER_SV57;			\
@@ -45,7 +45,7 @@
 	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_compat_task())			\
 		mmap_base = (_base);				\
 	else if (((_addr) >= VA_USER_SV57) && (VA_BITS >= VA_BITS_SV57)) \
 		mmap_base = VA_USER_SV57 - rnd_gap;		\
-- 
2.43.0

[PATCH v1 4/5] riscv: Introduce is_compat_thread() into compat.h

[Leonardo Bras]

task_user_regset_view() makes use of a function very similar to
is_compat_task(), but pointing to a any thread.

In arm64 asm/compat.h there is a function very similar to that:
is_compat_thread(struct thread_info *thread)

Copy this function to riscv asm/compat.h and make use of it into
task_user_regset_view().

Also, introduce a compile-time test for CONFIG_COMPAT and simplify the
function code by removing the #ifdef.

Signed-off-by: Leonardo Bras <leobras@redhat.com>
Reviewed-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Andy Chiu <andy.chiu@sifive.com>
---
 arch/riscv/include/asm/compat.h | 8 ++++++++
 arch/riscv/kernel/ptrace.c      | 6 +++---
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/include/asm/compat.h b/arch/riscv/include/asm/compat.h
index 91517b51b8e27..da4b28cd01a95 100644
--- a/arch/riscv/include/asm/compat.h
+++ b/arch/riscv/include/asm/compat.h
@@ -20,6 +20,14 @@ static inline int is_compat_task(void)
 	return test_thread_flag(TIF_32BIT);
 }
 
+static inline int is_compat_thread(struct thread_info *thread)
+{
+	if (!IS_ENABLED(CONFIG_COMPAT))
+		return 0;
+
+	return test_ti_thread_flag(thread, TIF_32BIT);
+}
+
 struct compat_user_regs_struct {
 	compat_ulong_t pc;
 	compat_ulong_t ra;
diff --git a/arch/riscv/kernel/ptrace.c b/arch/riscv/kernel/ptrace.c
index 2afe460de16a6..f362832123616 100644
--- a/arch/riscv/kernel/ptrace.c
+++ b/arch/riscv/kernel/ptrace.c
@@ -374,14 +374,14 @@ long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
 
 	return ret;
 }
+#else
+static const struct user_regset_view compat_riscv_user_native_view = {};
 #endif /* CONFIG_COMPAT */
 
 const struct user_regset_view *task_user_regset_view(struct task_struct *task)
 {
-#ifdef CONFIG_COMPAT
-	if (test_tsk_thread_flag(task, TIF_32BIT))
+	if (is_compat_thread(&task->thread_info))
 		return &compat_riscv_user_native_view;
 	else
-#endif
 		return &riscv_user_native_view;
 }
-- 
2.43.0

[PATCH v1 5/5] riscv: Introduce set_compat_task() in asm/compat.h

[Leonardo Bras]

In order to have all task compat bit access directly in compat.h, introduce
set_compat_task() to set/reset those when needed.

Also, since it's only used on an if/else scenario, simplify the macro using
it.

Signed-off-by: Leonardo Bras <leobras@redhat.com>
Reviewed-by: Guo Ren <guoren@kernel.org>
---
 arch/riscv/include/asm/compat.h | 8 ++++++++
 arch/riscv/include/asm/elf.h    | 5 +----
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/include/asm/compat.h b/arch/riscv/include/asm/compat.h
index da4b28cd01a95..aa103530a5c83 100644
--- a/arch/riscv/include/asm/compat.h
+++ b/arch/riscv/include/asm/compat.h
@@ -28,6 +28,14 @@ static inline int is_compat_thread(struct thread_info *thread)
 	return test_ti_thread_flag(thread, TIF_32BIT);
 }
 
+static inline void set_compat_task(bool is_compat)
+{
+	if (is_compat)
+		set_thread_flag(TIF_32BIT);
+	else
+		clear_thread_flag(TIF_32BIT);
+}
+
 struct compat_user_regs_struct {
 	compat_ulong_t pc;
 	compat_ulong_t ra;
diff --git a/arch/riscv/include/asm/elf.h b/arch/riscv/include/asm/elf.h
index 2e88257cafaea..c7aea7886d22a 100644
--- a/arch/riscv/include/asm/elf.h
+++ b/arch/riscv/include/asm/elf.h
@@ -135,10 +135,7 @@ do {							\
 #ifdef CONFIG_COMPAT
 
 #define SET_PERSONALITY(ex)					\
-do {    if ((ex).e_ident[EI_CLASS] == ELFCLASS32)		\
-		set_thread_flag(TIF_32BIT);			\
-	else							\
-		clear_thread_flag(TIF_32BIT);			\
+do {	set_compat_task((ex).e_ident[EI_CLASS] == ELFCLASS32);	\
 	if (personality(current->personality) != PER_LINUX32)	\
 		set_personality(PER_LINUX |			\
 			(current->personality & (~PER_MASK)));	\
-- 
2.43.0

Re: [PATCH v1 0/5] riscv: Introduce compat-mode helpers & improve arch_get_mmap_end()

[patchwork-bot+linux-riscv]

Hello:

This series was applied to riscv/linux.git (for-next)
by Palmer Dabbelt <palmer@rivosinc.com>:

On Wed,  3 Jan 2024 13:00:18 -0300 you wrote:
> I just saw the opportunity of optimizing the helper is_compat_task() by
> introducing a compile-time test, and it made possible to remove some
> #ifdef's without any loss of performance.
> 
> I also saw the possibility of removing the direct check of task flags from
> general code, and concentrated it in asm/compat.h by creating a few more
> helpers, which in the end helped optimize code.
> 
> [...]

Here is the summary with links:
  - [v1,1/5] riscv: Improve arch_get_mmap_end() macro
    https://git.kernel.org/riscv/c/6be7ee4bebd1
  - [v1,2/5] riscv: Replace direct thread flag check with is_compat_task()
    https://git.kernel.org/riscv/c/9dc30419248f
  - [v1,3/5] riscv: add compile-time test into is_compat_task()
    https://git.kernel.org/riscv/c/4c0b5a451675
  - [v1,4/5] riscv: Introduce is_compat_thread() into compat.h
    https://git.kernel.org/riscv/c/5917ea17ad07
  - [v1,5/5] riscv: Introduce set_compat_task() in asm/compat.h
    https://git.kernel.org/riscv/c/2a8986fc5e1c

You are awesome, thank you!
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