Re: [PATCH 3/3] riscv: mm: Do not restrict mmap address based on hint

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On 2024-08-27 00:36, Charlie Jenkins wrote:
The hint address should not forcefully restrict the addresses returned
by mmap as this causes mmap to report ENOMEM when there is memory still
available.

Signed-off-by: Charlie Jenkins <charlie@xxxxxxxxxxxx>
Fixes: b5b4287accd7 ("riscv: mm: Use hint address in mmap if available")
Fixes: add2cc6b6515 ("RISC-V: mm: Restrict address space for sv39,sv48,sv57")
Closes: https://lore.kernel.org/linux-kernel/ZbxTNjQPFKBatMq+@ghost/T/#mccb1890466bf5a488c9ce7441e57e42271895765
---
  arch/riscv/include/asm/processor.h | 26 ++------------------------
  1 file changed, 2 insertions(+), 24 deletions(-)

diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
index 8702b8721a27..efa1b3519b23 100644
--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -14,36 +14,14 @@
#include <asm/ptrace.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)))			\
-		mmap_end = STACK_TOP_MAX;			\
-	else							\
-		mmap_end = (_addr + len);			\
-	mmap_end;						\
+	STACK_TOP_MAX;						\
  })
#define arch_get_mmap_base(addr, base) \
  ({								\
-	unsigned long mmap_base;				\
-	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);				\
-	else							\
-		mmap_base = (_addr + len) - rnd_gap;		\
-	mmap_base;						\
+	base;							\
  })
#ifdef CONFIG_64BIT

I tested this patch on 6.10.2 kernel and could confirm that it fixes the crash of chromium. But I think I prefer Yangyu Chen's approach because that would avoid breaking some applications on sv57.

Tested-by: Levi Zim <rsworktech@xxxxxxxxxxx> # Chromium, sv39





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