[PATCH 1/4] powerpc/tm: Add commandline option to disable hardware transactional memory

[Michael Neuling]

On Fri, 2017-10-20 at 09:45 -0200, Breno Leitao wrote:
> Mikey, Cyril,
> 
> On Thu, Oct 12, 2017 at 09:17:16PM +1100, Michael Ellerman wrote:
> > From: Cyril Bur <cyrilbur at gmail.com>
> > 
> > Currently the kernel relies on firmware to inform it whether or not the
> > CPU supports HTM and as long as the kernel was built with
> > CONFIG_PPC_TRANSACTIONAL_MEM=y then it will allow userspace to make
> > use of the facility.
> > 
> > There may be situations where it would be advantageous for the kernel
> > to not allow userspace to use HTM, currently the only way to achieve
> > this is to recompile the kernel with CONFIG_PPC_TRANSACTIONAL_MEM=n.
> > 
> > This patch adds a simple commandline option so that HTM can be
> > disabled at boot time.
> > 
> > Signed-off-by: Cyril Bur <cyrilbur at gmail.com>
> > [mpe: Simplify to a bool, move to prom.c, put doco in the right place.
> >  Always disable, regardless of initial state, to avoid user confusion.]
> > Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
> > ---
> >  Documentation/admin-guide/kernel-parameters.txt |  4 ++++
> >  arch/powerpc/kernel/prom.c                      | 31
> > +++++++++++++++++++++++++
> >  2 files changed, 35 insertions(+)
> > 
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt
> > b/Documentation/admin-guide/kernel-parameters.txt
> > index 05496622b4ef..ef03e6e16bdb 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -3185,6 +3185,10 @@
> >  			allowed (eg
> > kernel_enable_fpu()/kernel_disable_fpu()).
> >  			There is some performance impact when enabling
> > this.
> >  
> > +	ppc_tm=		[PPC]
> > +			Format: {"off"}
> > +			Disable Hardware Transactional Memory
> > +
> >  	print-fatal-signals=
> >  			[KNL] debug: print fatal signals
> >  
> > diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
> > index f83056297441..d9bd6555f980 100644
> > --- a/arch/powerpc/kernel/prom.c
> > +++ b/arch/powerpc/kernel/prom.c
> > @@ -658,6 +658,35 @@ static void __init early_reserve_mem(void)
> >  #endif
> >  }
> >  
> > +#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
> > +static bool tm_disabled __initdata;
> 
> I think the name 'tm_disabled' might cause more confusion on the TM
> code. Mainly because we already have tm_enable() and tm_enabled()
> functions which are related to the MSR register and TM bit, and, with
> your new variable, tm_enabled() and tm_disabled are not going to be
> exclusionary. Neither tm_enable() with be able to toggle the tm_disabled
> value.

Got a proposal for better names?

Mikey