linux-kernel - [PATCH 6.6.y 1/2] riscv: mm: Use hint address in mmap if available

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Message-Id: <20251008-riscv-mmap-addr-space-6-6-v1-1-9f47574a520f@iscas.ac.cn>
Date: Wed, 08 Oct 2025 15:50:16 +0800
From: Vivian Wang <wangruikang@...as.ac.cn>
To: stable@...r.kernel.org, Paul Walmsley <pjw@...nel.org>, 
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
 Paul Walmsley <paul.walmsley@...ive.com>
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, 
 Guo Ren <guoren@...nel.org>, Charlie Jenkins <charlie@...osinc.com>, 
 Yangyu Chen <cyy@...self.name>, Han Gao <rabenda.cn@...il.com>, 
 Icenowy Zheng <uwu@...nowy.me>, Inochi Amaoto <inochiama@...il.com>, 
 Vivian Wang <wangruikang@...as.ac.cn>, Yao Zi <ziyao@...root.org>, 
 Palmer Dabbelt <palmer@...osinc.com>
Subject: [PATCH 6.6.y 1/2] riscv: mm: Use hint address in mmap if available

From: Charlie Jenkins <charlie@...osinc.com>

[ Upstream commit b5b4287accd702f562a49a60b10dbfaf7d40270f ]

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@...osinc.com>
Link: https://lore.kernel.org/r/20240130-use_mmap_hint_address-v3-1-8a655cfa8bcb@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@...osinc.com>
[ Adjust TASK_SIZE64 -> TASK_SIZE in moved lines ]
Signed-off-by: Vivian Wang <wangruikang@...as.ac.cn>
Tested-by: Han Gao <rabenda.cn@...il.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 4f6af8c6cfa060380594c6d0e727af6b02d08d70..938aef30dfb42ee477b7c59b5d2afc3871d8004d 100644
--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -13,22 +13,16 @@
 
 #include <asm/ptrace.h>
 
-#ifdef CONFIG_64BIT
-#define DEFAULT_MAP_WINDOW	(UL(1) << (MMAP_VA_BITS - 1))
-#define STACK_TOP_MAX		TASK_SIZE
-
 #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;						\
 })
 
@@ -38,17 +32,18 @@
 	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
 #else
 #define DEFAULT_MAP_WINDOW	TASK_SIZE
 #define STACK_TOP_MAX		TASK_SIZE

-- 
2.50.1