On Tue, 01 May 2018 21:11:06 +1000 Michael Ellerman <m...@ellerman.id.au> wrote:
> Michal Suchánek <msucha...@suse.de> writes: > > Hello, > > > > On Tue, 24 Apr 2018 14:15:57 +1000 > > Michael Ellerman <m...@ellerman.id.au> wrote: > > > >> From: Michal Suchanek <msucha...@suse.de> > >> > >> Check what firmware told us and enable/disable the barrier_nospec > >> as appropriate. > >> > >> We err on the side of enabling the barrier, as it's no-op on older > >> systems, see the comment for more detail. > >> > >> Signed-off-by: Michael Ellerman <m...@ellerman.id.au> > ... > > > > I am missing the option for the barrier to be disabled by a kernel > > commandline argument here. > > > > It does make sense to add a kernel parameter that is checked on > > boot to be compatible with other platforms that implement one. > > No other platforms have an option to disable variant 1 mitigations, so > there isn't an existing parameter we can use. Right, I was looking at an older implementation which turned off both v1 and v2 with same parameter. In current kernel the v1 mitigation is not turned off at all. > > Which is not to say we can't add one, but I wasn't sure if it was > really worth it. The current thinking is that most performance relevant cases are covered with array_nospec which has little overhead. The less code we have for this the better ;-) Thanks Michal
