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To:     Michal Suchanek <msuchanek@suse.de>,
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Subject: Re: [PATCH RFC rebase 9/9] powerpc/64: barrier_nospec: Add
 commandline trigger
Thread-Topic: [PATCH RFC rebase 9/9] powerpc/64: barrier_nospec: Add
 commandline trigger
Thread-Index: AQHTvJSv3hggio9YDU6ISyDW5QYSAw==
Date:   Fri, 23 Mar 2018 15:59:50 +0000
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On 3/15/2018 9:34 PM, Michal Suchanek wrote:=0A=
> Add commandline options spectre_v2 and nospectre_v2=0A=
>=0A=
> These are named same as similar x86 options regardless of actual effect=
=0A=
> to not require platform-specific configuration.=0A=
>=0A=
> Supported options:=0A=
> nospectre_v2 or spectre_v2=3Doff - speculation barrier not used=0A=
> spectre_v2=3Don or spectre_v2=3Dauto - speculation barrier used=0A=
=0A=
Why the barrier is enabled only for spectre variant 2 mitigations? It=0A=
can be used as well for variant 1 mitigations. In fact I am not sure=0A=
that the places where it is used fall under spectre 2 at all.=0A=
=0A=
>=0A=
> Changing the settings after boot is not supported and VM migration may=0A=
> change requirements so auto is same as on.=0A=
>=0A=
> Based on s390 implementation=0A=
>=0A=
> Signed-off-by: Michal Suchanek <msuchanek@suse.de>=0A=
> ---=0A=
>  arch/powerpc/kernel/setup_64.c | 22 ++++++++++++++++++++++=0A=
>  1 file changed, 22 insertions(+)=0A=
>=0A=
> diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_6=
4.c=0A=
> index f6678a7b6114..c74e656265df 100644=0A=
> --- a/arch/powerpc/kernel/setup_64.c=0A=
> +++ b/arch/powerpc/kernel/setup_64.c=0A=
> @@ -840,6 +840,28 @@ static int __init handle_no_pti(char *p)=0A=
>  }=0A=
>  early_param("nopti", handle_no_pti);=0A=
>  =0A=
> +static int __init nospectre_v2_setup_early(char *str)=0A=
> +{=0A=
> +	no_nospec =3D true;=0A=
> +	return 0;=0A=
> +}=0A=
> +early_param("nospectre_v2", nospectre_v2_setup_early);=0A=
> +=0A=
> +static int __init spectre_v2_setup_early(char *str)=0A=
> +{=0A=
> +	if (str && !strncmp(str, "on", 2))=0A=
> +		no_nospec =3D false;=0A=
> +=0A=
> +	if (str && !strncmp(str, "off", 3))=0A=
> +		no_nospec =3D true;=0A=
> +=0A=
> +	if (str && !strncmp(str, "auto", 4))=0A=
> +		no_nospec =3D false;=0A=
> +=0A=
> +	return 0;=0A=
> +}=0A=
> +early_param("spectre_v2", spectre_v2_setup_early);=0A=
> +=0A=
>  static void do_nothing(void *unused)=0A=
>  {=0A=
>  	/*=0A=
=0A=
Thanks,=0A=
=0A=
Diana=0A=
=0A=