Re: [PATCH v3 2/3] selftests/resctrl: Implement cl_flush() and sb() for aarch64

[Reinette Chatre <reinette.chatre@intel.com>]

+Ben

Hi Richard,

On 5/28/26 7:23 PM, Richard Cheng wrote:
> cl_flush() and sb() in fill_buf.c only have implementations for i386
> and x86_64, so on aarch64 both compile to empty functions. mem_flush()
> then walks the buffer calling a no-op cl_flush() per cache line and
> finishes with a no-op sb(), leaving any caller that expects a flushed
> buffer (e.g. CMT, L3_CAT) operating on unflushed state with no warning.
> 
> Add an aarch64 code block using the ARM equivalents:
> * "dc civac, %0" for cl_flush()
> * "dsb sy"       for sb()

Calling on Arm experts here since my superficial check found sfence to
be used for __wmb() on x86 and the Arm equivalent per
arch/arm64/include/asm/barrier.h appears to be "dsb st"?

Even so, it looks like the changes below were considered by Ben during
a previous submission but I am not able to tell if his feedback was taken
into account here.
Please see:
https://lore.kernel.org/lkml/4449219d-186f-4b5e-9f72-958d1af80f58@arm.com/
https://lore.kernel.org/lkml/5aea412c-9c7f-4692-af3e-79937956ef8c@arm.com/

> 
> Both instructions are EL0-accessible on Linux aarch64.
> 
> Signed-off-by: Richard Cheng <icheng@nvidia.com>
> ---
>  tools/testing/selftests/resctrl/fill_buf.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/tools/testing/selftests/resctrl/fill_buf.c b/tools/testing/selftests/resctrl/fill_buf.c
> index 19a01a52dc1a..a41d21e5a64e 100644
> --- a/tools/testing/selftests/resctrl/fill_buf.c
> +++ b/tools/testing/selftests/resctrl/fill_buf.c
> @@ -27,6 +27,9 @@ static void sb(void)
>  #if defined(__i386) || defined(__x86_64)
>  	asm volatile("sfence\n\t"
>  		     : : : "memory");
> +#elif defined(__aarch64__)
> +	asm volatile("dsb sy\n\t"
> +		     : : : "memory");
>  #endif
>  }
>  
> @@ -35,6 +38,9 @@ static void cl_flush(void *p)
>  #if defined(__i386) || defined(__x86_64)
>  	asm volatile("clflush (%0)\n\t"
>  		     : : "r"(p) : "memory");
> +#elif defined(__aarch64__)
> +	asm volatile("dc civac, %0\n\t"
> +		     : : "r"(p) : "memory");
>  #endif
>  }
>  

Reinette