linux-kernel - [PATCH v3 2/3] RISC-V: mm: not use hint addr as upper bound

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Message-ID: <tencent_C8DB706163A442181BBBF946053FB4311C09@qq.com>
Date: Tue, 27 Aug 2024 16:07:06 +0800
From: Yangyu Chen <cyy@...self.name>
To: linux-riscv@...ts.infradead.org
Cc: Charlie Jenkins <charlie@...osinc.com>,
	Jonathan Corbet <corbet@....net>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Shuah Khan <shuah@...nel.org>,
	Levi Zim <rsworktech@...look.com>,
	Alexandre Ghiti <alexghiti@...osinc.com>,
	linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Palmer Dabbelt <palmer@...osinc.com>,
	linux-kselftest@...r.kernel.org,
	Yangyu Chen <cyy@...self.name>
Subject: [PATCH v3 2/3] RISC-V: mm: not use hint addr as upper bound

This patch reverted the meaning of the addr parameter in the mmap syscall
change from the previous commit b5b4287accd7 ("riscv: mm: Use hint address
in mmap if available") from patch[1] which treats hint addr + size as the
upper bound of the mmap return address. Result in ENOMEM error caused when
hint address + size is not big enough.

Thus, this patch makes the behavior of mmap syscall to align with x86,
arm64, powerpc by only limiting the address space to DEFAULT_MAP_WINDOW
which is defined as not larger than 47-bit. If a user program wants to
use sv57 address space, it can use mmap with a hint address larger than
BIT(47) as it is already documented in x86 and arm64.

[1] https://lore.kernel.org/linux-riscv/20240130-use_mmap_hint_address-v3-0-8a655cfa8bcb@rivosinc.com/

Signed-off-by: Yangyu Chen <cyy@...self.name>
---
 arch/riscv/include/asm/processor.h | 20 +++++++-------------
 1 file changed, 7 insertions(+), 13 deletions(-)

diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
index 8702b8721a27..faf3e230ab24 100644
--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -13,22 +13,17 @@
 #include <vdso/processor.h>
 
 #include <asm/ptrace.h>
+#include <asm/mman.h>
 
-/*
- * 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_compat_task() ||			\
-	    ((_addr + len) > BIT(VA_BITS - 1)))			\
+	if (((_addr + len) > DEFAULT_MAP_WINDOW) ||		\
+	    ((flags) & MAP_FIXED))				\
 		mmap_end = STACK_TOP_MAX;			\
 	else							\
-		mmap_end = (_addr + len);			\
+		mmap_end = DEFAULT_MAP_WINDOW;			\
 	mmap_end;						\
 })
 
@@ -38,11 +33,10 @@
 	typeof(addr) _addr = (addr);				\
 	typeof(base) _base = (base);				\
 	unsigned long rnd_gap = DEFAULT_MAP_WINDOW - (_base);	\
-	if ((_addr) == 0 || is_compat_task() || 		\
-	    ((_addr + len) > BIT(VA_BITS - 1)))			\
-		mmap_base = (_base);				\
+	if ((_addr + len) > DEFAULT_MAP_WINDOW)			\
+		mmap_base = (STACK_TOP_MAX - rnd_gap);		\
 	else							\
-		mmap_base = (_addr + len) - rnd_gap;		\
+		mmap_base = (_base);				\
 	mmap_base;						\
 })
 
-- 
2.45.2