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    SubjectRe: [PATCH 4.19 056/191] powerpc: select ARCH_WANT_IRQS_OFF_ACTIVATE_MM
    Date
    Greg Kroah-Hartman <gregkh@linuxfoundation.org> writes:
    > From: Nicholas Piggin <npiggin@gmail.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@gmail.com>
    > Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    > Link: https://lore.kernel.org/r/20200914045219.3736466-3-npiggin@gmail.com
    > Signed-off-by: Sasha Levin <sashal@kernel.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.

    cheers

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