linux-kernel - Re: [PATCH RFC 3/5] powerpc/speculation: Add support for 'cpu_spec

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Date:   Wed, 10 Apr 2019 23:02:22 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Kosina <jikos@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Jon Masters <jcm@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        linux-s390@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tyler Hicks <tyhicks@...onical.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH RFC 3/5] powerpc/speculation: Add support for
 'cpu_spec_mitigations=' cmdline options

On Wed, Apr 10, 2019 at 04:06:50PM +1000, Michael Ellerman wrote:
> Josh Poimboeuf <jpoimboe@...hat.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@...hat.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