linux-kernel - Re: [PATCH 4.19 056/191] powerpc: select ARCH_WANT_IRQS_OFF_ACTIVATE

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Message-ID: <20201104090549.GB1588160@kroah.com>
Date:   Wed, 4 Nov 2020 10:05:49 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Nicholas Piggin <npiggin@...il.com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 056/191] powerpc: select
 ARCH_WANT_IRQS_OFF_ACTIVATE_MM

On Wed, Nov 04, 2020 at 12:19:45PM +1100, Michael Ellerman wrote:
> Michael Ellerman <mpe@...erman.id.au> writes:
> > Greg Kroah-Hartman <gregkh@...uxfoundation.org> writes:
> >> From: Nicholas Piggin <npiggin@...il.com>
> >>
> >> [ 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@...il.com>
> >> Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
> >> Link: https://lore.kernel.org/r/20200914045219.3736466-3-npiggin@gmail.com
> >> Signed-off-by: Sasha Levin <sashal@...nel.org>
> >> ---
> >>  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.
> 
> I just sent you a backport of d53c3dfb23c4 for 4.19.

I've taken that at the proper part of this series now, thanks!

greg k-h