Re: [PATCH] powerpc/64s: support nospectre_v2 cmdline option

[Andrew Donnellan <ajd@linux.ibm.com>]

On 6/5/19 8:10 am, Christopher M. Riedl wrote:
> Add support for disabling the kernel implemented spectre v2 mitigation
> (count cache flush on context switch) via the nospectre_v2 cmdline
> option.
> 
> Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
> Signed-off-by: Christopher M. Riedl <cmr@informatik.wtf>
> ---
> 
>   arch/powerpc/kernel/security.c | 14 ++++++++++++--
>   1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/security.c b/arch/powerpc/kernel/security.c
> index b33bafb8fcea..f7c34745cd0f 100644
> --- a/arch/powerpc/kernel/security.c
> +++ b/arch/powerpc/kernel/security.c
> @@ -28,7 +28,7 @@ static enum count_cache_flush_type count_cache_flush_type = COUNT_CACHE_FLUSH_NO
>   bool barrier_nospec_enabled;
>   static bool no_nospec;
>   static bool btb_flush_enabled;
> -#ifdef CONFIG_PPC_FSL_BOOK3E
> +#if defined(CONFIG_PPC_FSL_BOOK3E) || defined(CONFIG_PPC_BOOK3S_64)
>   static bool no_spectrev2;
>   #endif
>   
> @@ -106,7 +106,7 @@ static __init int barrier_nospec_debugfs_init(void)
>   device_initcall(barrier_nospec_debugfs_init);
>   #endif /* CONFIG_DEBUG_FS */
>   
> -#ifdef CONFIG_PPC_FSL_BOOK3E
> +#if defined(CONFIG_PPC_FSL_BOOK3E) || defined(CONFIG_PPC_BOOK3S_64)
>   static int __init handle_nospectre_v2(char *p)
>   {
>   	no_spectrev2 = true;
> @@ -114,6 +114,9 @@ static int __init handle_nospectre_v2(char *p)
>   	return 0;
>   }
>   early_param("nospectre_v2", handle_nospectre_v2);
> +#endif /* CONFIG_PPC_FSL_BOOK3E || CONFIG_PPC_BOOK3S_64 */
> +
> +#ifdef CONFIG_PPC_FSL_BOOK3E
>   void setup_spectre_v2(void)
>   {
>   	if (no_spectrev2)
> @@ -391,6 +394,13 @@ static void toggle_count_cache_flush(bool enable)
>   
>   void setup_count_cache_flush(void)
>   {
> +	if (no_spectrev2) {
> +		if (security_ftr_enabled(SEC_FTR_BCCTRL_SERIALISED)
> +		    || security_ftr_enabled(SEC_FTR_COUNT_CACHE_DISABLED))
> +			pr_warn("Spectre v2 mitigations not under software control, can't disable\n");

If one of those ftrs is set, what's the impact of not calling 
toggle_count_cache_flush()?

> +		return;
> +	}
> +
>   	toggle_count_cache_flush(true);
>   }
>   
> 

-- 
Andrew Donnellan              OzLabs, ADL Canberra
ajd@linux.ibm.com             IBM Australia Limited