On Tue, Nov 17, 2020 at 07:45:28PM -0500, Sasha Levin wrote: > On Tue, Nov 17, 2020 at 10:51:16AM -0800, Kamal Mostafa wrote: > > On Tue, Nov 3, 2020 at 4:22 PM Michael Ellerman <mpe@xxxxxxxxxxxxxx> wrote: > > > > > Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> writes: > > > > From: Nicholas Piggin <npiggin@xxxxxxxxx> > > > > > > > > [ Upstream commit 66acd46080bd9e5ad2be4b0eb1d498d5145d058e ] > > > > > > > > powerpc uses IPIs in some situations to switch a kernel thread away > > > > from a lazy tlb mm, which is subject to the TLB flushing race > > > > described in the changelog introducing ARCH_WANT_IRQS_OFF_ACTIVATE_MM. > > > > > > > > Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx> > > > > Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> > > > > Link: > > > https://lore.kernel.org/r/20200914045219.3736466-3-npiggin@xxxxxxxxx > > > > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> > > > > --- > > > > arch/powerpc/Kconfig | 1 + > > > > arch/powerpc/include/asm/mmu_context.h | 2 +- > > > > 2 files changed, 2 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig > > > > index f38d153d25861..0bc53f0e37c0f 100644 > > > > --- a/arch/powerpc/Kconfig > > > > +++ b/arch/powerpc/Kconfig > > > > @@ -152,6 +152,7 @@ config PPC > > > > select ARCH_USE_BUILTIN_BSWAP > > > > select ARCH_USE_CMPXCHG_LOCKREF if PPC64 > > > > select ARCH_WANT_IPC_PARSE_VERSION > > > > + select ARCH_WANT_IRQS_OFF_ACTIVATE_MM > > > > > > This depends on upstream commit: > > > > > > d53c3dfb23c4 ("mm: fix exec activate_mm vs TLB shootdown and lazy tlb > > > switching race") > > > > > > > > > Which I don't see in 4.19 stable, or in the email thread here. > > > > > > So this shouldn't be backported to 4.19 unless that commit is also > > > backported. > > > > > > cheers > > > > > > > Hi- > > > > This glitch has made its way into 4.14.y ... > > [4.14.y] c2bca8712a19 powerpc: select ARCH_WANT_IRQS_OFF_ACTIVATE_MM > > But 4.14.y does not carry the prereq that introduces that config. > > I'll queue up the 4.19 backport for 4.14 too, thanks! > Thanks Sasha. And nevermind my other concern ... > > It would seem that the intent is that it should be *only* enabled > > (currently at least) for arches that will explicitly select it, but the > > config advice does not make that very clear. Could that new config get > > an explicit "default n" line? ... I see now that a 'default' isn't necessary; the config only appears for arches which explicitly select it, as intended. -Kamal
