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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Nicholas Piggin <npiggin@gmail.com>,
        Sasha Levin <sashal@kernel.org>
Subject: Re: [PATCH 4.19 056/191] powerpc: select ARCH_WANT_IRQS_OFF_ACTIVATE_MM
In-Reply-To: <87361qug5a.fsf@mpe.ellerman.id.au>
References: <20201103203232.656475008@linuxfoundation.org> <20201103203239.940977599@linuxfoundation.org> <87361qug5a.fsf@mpe.ellerman.id.au>
Date:   Wed, 04 Nov 2020 12:19:45 +1100
Message-ID: <87zh3xude6.fsf@mpe.ellerman.id.au>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

Michael Ellerman <mpe@ellerman.id.au> writes:
> 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.

I just sent you a backport of d53c3dfb23c4 for 4.19.

cheers