Re: [PATCH RFC 3/5] powerpc/speculation: Add support for 'cpu_spec_mitigations=' cmdline options

Josh Poimboeuf
2019-04-11T04:02:49Z

On Wed, Apr 10, 2019 at 04:06:50PM +1000, Michael Ellerman wrote:
> Josh Poimboeuf <jpoimboe@redhat.com> writes:
> > Configure powerpc CPU runtime speculation bug mitigations in accordance
> > with the 'cpu_spec_mitigations=' cmdline options. This affects
> > Meltdown, Spectre v1, Spectre v2, and Speculative Store Bypass.
> >
> > The default behavior is unchanged.
> >
> > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> > ---
> > Documentation/admin-guide/kernel-parameters.txt | 9 +++++----
> > arch/powerpc/kernel/security.c | 6 +++---
> > arch/powerpc/kernel/setup_64.c | 2 +-
> > 3 files changed, 9 insertions(+), 8 deletions(-)
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index 29dc03971630..0e8eae1e8a25 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -2552,10 +2552,11 @@
> >
> > off
> > Disable all speculative CPU mitigations.
> > - Equivalent to: nopti [x86]
> > + Equivalent to: nopti [x86, powerpc]
> > + nospectre_v1 [powerpc]
> > nospectre_v2 [x86]
>
> Not sure if you meant to omit powerpc from nospectre_v2?
>
> You have patched it in the code below.

Oops. I'll update the documentation.

> > spectre_v2_user=off [x86]
> > - spec_store_bypass_disable=off [x86]
> > + spec_store_bypass_disable=off [x86, powerpc]
> > l1tf=off [x86]
> >
> > auto (default)
> > @@ -2568,7 +2569,7 @@
> > Equivalent to: pti=auto [x86]
> > spectre_v2=auto [x86]
> > spectre_v2_user=auto [x86]
> > - spec_store_bypass_disable=auto [x86]
> > + spec_store_bypass_disable=auto [x86, powerpc]
> > l1tf=flush [x86]
> >
> > auto,nosmt
> > @@ -2579,7 +2580,7 @@
> > Equivalent to: pti=auto [x86]
> > spectre_v2=auto [x86]
> > spectre_v2_user=auto [x86]
> > - spec_store_bypass_disable=auto [x86]
> > + spec_store_bypass_disable=auto [x86, powerpc]
> > l1tf=flush,nosmt [x86]
> >
> > mminit_loglevel=
> > diff --git a/arch/powerpc/kernel/security.c b/arch/powerpc/kernel/security.c
> > index b33bafb8fcea..5aed4ad729ba 100644
> > --- a/arch/powerpc/kernel/security.c
> > +++ b/arch/powerpc/kernel/security.c
> > @@ -57,7 +57,7 @@ void setup_barrier_nospec(void)
> > enable = security_ftr_enabled(SEC_FTR_FAVOUR_SECURITY) &&
> > security_ftr_enabled(SEC_FTR_BNDS_CHK_SPEC_BAR);
> >
> > - if (!no_nospec)
> > + if (!no_nospec && cpu_spec_mitigations != CPU_SPEC_MITIGATIONS_OFF)
> > enable_barrier_nospec(enable);
>
> Adding a wrapper func that checks for CPU_SPEC_MITIGATIONS_OFF would
> make these a little less verbose, eg:
>
> if (!no_nospec && !cpu_spec_mitigations_off())
> enable_barrier_nospec(enable);
>
> But that's a nitpick.

Yes, that would be much nicer. I'll probably do something like that in
the next version. Thanks.

--
Josh