2024-01-09 14:46:45

by Yangyu Chen

Subject: [PATCH] asm-generic: flush icache only when vma->vm_flags has VM_EXEC set

For some ISAs like RISC-V, which may not support bus broadcast-based
icache flushing instructions, it's necessary to send IPIs to all of the
CPUs in the system to flush the icache. This process can be expensive for
these ISAs and introduce disturbances during performance profiling.
Limiting the icache flush to occur only when the vma->vm_flags has VM_EXEC
can help minimize the frequency of these operations.

Signed-off-by: Yangyu Chen <[email protected]>
---
include/asm-generic/cacheflush.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/asm-generic/cacheflush.h b/include/asm-generic/cacheflush.h
index 84ec53ccc450..729d51536575 100644
--- a/include/asm-generic/cacheflush.h
+++ b/include/asm-generic/cacheflush.h
@@ -102,7 +102,8 @@ static inline void flush_cache_vunmap(unsigned long start, unsigned long end)
do { \
instrument_copy_to_user((void __user *)dst, src, len); \
memcpy(dst, src, len); \
- flush_icache_user_page(vma, page, vaddr, len); \
+ if (vma->vm_flags & VM_EXEC) \
+ flush_icache_user_page(vma, page, vaddr, len); \
} while (0)
#endif

--
2.43.0

2024-01-10 11:30:01

by Arnd Bergmann

Subject: Re: [PATCH] asm-generic: flush icache only when vma->vm_flags has VM_EXEC set

On Tue, Jan 9, 2024, at 15:45, Yangyu Chen wrote:
> For some ISAs like RISC-V, which may not support bus broadcast-based
> icache flushing instructions, it's necessary to send IPIs to all of the
> CPUs in the system to flush the icache. This process can be expensive for
> these ISAs and introduce disturbances during performance profiling.
> Limiting the icache flush to occur only when the vma->vm_flags has VM_EXEC
> can help minimize the frequency of these operations.
>
> Signed-off-by: Yangyu Chen <[email protected]>
> ---
> include/asm-generic/cacheflush.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/include/asm-generic/cacheflush.h
> b/include/asm-generic/cacheflush.h
> index 84ec53ccc450..729d51536575 100644
> --- a/include/asm-generic/cacheflush.h
> +++ b/include/asm-generic/cacheflush.h
> @@ -102,7 +102,8 @@ static inline void flush_cache_vunmap(unsigned long
> start, unsigned long end)
> do { \
> instrument_copy_to_user((void __user *)dst, src, len); \
> memcpy(dst, src, len); \
> - flush_icache_user_page(vma, page, vaddr, len); \
> + if (vma->vm_flags & VM_EXEC) \
> + flush_icache_user_page(vma, page, vaddr, len); \
> } while (0)
> #endif

This is not my normal area of expertise, but I wonder if you can't
just do this the same way as alpha and openrisc by having the
condition in architecture specific code.

Arnd