Re: [PATCH] powerpc/64s: Allow control of RFI flush via debugfs

[Nicholas Piggin <npiggin@gmail.com>]

On Tue, 16 Jan 2018 22:24:31 +1100
Michael Ellerman <mpe@ellerman.id.au> wrote:

> Expose the state of the RFI flush (enabled/disabled) via debugfs, and
> allow it to be enabled/disabled at runtime.
> 
> eg: $ cat /sys/kernel/debug/powerpc/rfi_flush
>     1
>     $ echo 0 > /sys/kernel/debug/powerpc/rfi_flush
>     $ cat /sys/kernel/debug/powerpc/rfi_flush
>     0
> 
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

> ---
>  arch/powerpc/kernel/setup_64.c | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
> index 624d2a62d05d..e67413f4a8f0 100644
> --- a/arch/powerpc/kernel/setup_64.c
> +++ b/arch/powerpc/kernel/setup_64.c
> @@ -38,6 +38,7 @@
>  #include <linux/memory.h>
>  #include <linux/nmi.h>
>  
> +#include <asm/debugfs.h>
>  #include <asm/io.h>
>  #include <asm/kdump.h>
>  #include <asm/prom.h>
> @@ -902,6 +903,35 @@ void __init setup_rfi_flush(enum l1d_flush_type types, bool enable)
>  		rfi_flush_enable(enable);
>  }
>  
> +#ifdef CONFIG_DEBUG_FS
> +static int rfi_flush_set(void *data, u64 val)
> +{
> +	if (val == 1)
> +		rfi_flush_enable(true);
> +	else if (val == 0)
> +		rfi_flush_enable(false);
> +	else
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +
> +static int rfi_flush_get(void *data, u64 *val)
> +{
> +	*val = rfi_flush ? 1 : 0;
> +	return 0;
> +}
> +
> +DEFINE_SIMPLE_ATTRIBUTE(fops_rfi_flush, rfi_flush_get, rfi_flush_set, "%llu\n");
> +
> +static __init int rfi_flush_debugfs_init(void)
> +{
> +	debugfs_create_file("rfi_flush", 0600, powerpc_debugfs_root, NULL, &fops_rfi_flush);
> +	return 0;
> +}
> +device_initcall(rfi_flush_debugfs_init);
> +#endif
> +
>  ssize_t cpu_show_meltdown(struct device *dev, struct device_attribute *attr, char *buf)
>  {
>  	if (rfi_flush)