On Sat, Oct 21, 2017 at 11:58:47AM +1100, Michael Neuling wrote:
> 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 <cyril...@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 <cyril...@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 <m...@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?
That is the hardest part, but I thought about something as:
* tm_disabled_on_boot
* tm_off
* tm_explicit_disabled
* tm_feature_disabled
* tm_enablement_disabled
I think these names, although a bit longer, might avoid the confusion
with tm_enable/tm_enabled nomenclature.
