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Subject: Re: [PATCH AUTOSEL 6.3 08/59] bpf, mips: Implement DADDI workarounds
 for JIT
From:   Jiaxun Yang <jiaxun.yang@flygoat.com>
In-Reply-To: <20230504194142.3805425-8-sashal@kernel.org>
Date:   Fri, 5 May 2023 13:04:14 +0100
Cc:     linux-kernel@vger.kernel.org,
        "stable@vger.kernel.org" <stable@vger.kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        =?utf-8?Q?Philippe_Mathieu-Daud=C3=A9?= <philmd@linaro.org>,
        Johan Almbladh <johan.almbladh@anyfinetworks.com>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Alexei Starovoitov <ast@kernel.org>,
        Andrii Nakryiko <andrii@kernel.org>,
        "paulburton@kernel.org" <paulburton@kernel.org>,
        "linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>,
        bpf@vger.kernel.org
Content-Transfer-Encoding: quoted-printable
Message-Id: <50FCC591-D86A-46A3-AF4A-DD68D2FACC78@flygoat.com>
References: <20230504194142.3805425-1-sashal@kernel.org>
 <20230504194142.3805425-8-sashal@kernel.org>
To:     Sasha Levin <sashal@kernel.org>
Precedence: bulk


> 2023=E5=B9=B45=E6=9C=884=E6=97=A5 20:40=EF=BC=8CSasha Levin =
<sashal@kernel.org> =E5=86=99=E9=81=93=EF=BC=9A
>=20
> From: Jiaxun Yang <jiaxun.yang@flygoat.com>
>=20
> [ Upstream commit bbefef2f07080cd502a93cb1c529e1c8a6c4ac8e ]
>=20
> For DADDI errata we just workaround by disable immediate operation
> for BPF_ADD / BPF_SUB to avoid generation of DADDIU.
>=20
> All other use cases in JIT won't cause overflow thus they are all =
safe.
>=20
> Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> Reviewed-by: Philippe Mathieu-Daud=C3=A9 <philmd@linaro.org>
> Acked-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
> Link: =
https://lore.kernel.org/bpf/20230228113305.83751-2-jiaxun.yang@flygoat.com=

> Signed-off-by: Sasha Levin <sashal@kernel.org>

Hi Sasha,

I think this patch should count as a functional improvement instead of =
regression fix.

Please drop it from stable queue.

Thanks
Jiaxun

> ---
> arch/mips/Kconfig            | 1 -
> arch/mips/net/bpf_jit_comp.c | 4 ++++
> 2 files changed, 4 insertions(+), 1 deletion(-)
>=20
> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> index e2f3ca73f40d6..edc7d8790f1e8 100644
> --- a/arch/mips/Kconfig
> +++ b/arch/mips/Kconfig
> @@ -64,7 +64,6 @@ config MIPS
> select HAVE_DMA_CONTIGUOUS
> select HAVE_DYNAMIC_FTRACE
> select HAVE_EBPF_JIT if !CPU_MICROMIPS && \
> - !CPU_DADDI_WORKAROUNDS && \
> !CPU_R4000_WORKAROUNDS && \
> !CPU_R4400_WORKAROUNDS
> select HAVE_EXIT_THREAD
> diff --git a/arch/mips/net/bpf_jit_comp.c =
b/arch/mips/net/bpf_jit_comp.c
> index b17130d510d49..a40d926b65139 100644
> --- a/arch/mips/net/bpf_jit_comp.c
> +++ b/arch/mips/net/bpf_jit_comp.c
> @@ -218,9 +218,13 @@ bool valid_alu_i(u8 op, s32 imm)
> /* All legal eBPF values are valid */
> return true;
> case BPF_ADD:
> + if (IS_ENABLED(CONFIG_CPU_DADDI_WORKAROUNDS))
> + return false;
> /* imm must be 16 bits */
> return imm >=3D -0x8000 && imm <=3D 0x7fff;
> case BPF_SUB:
> + if (IS_ENABLED(CONFIG_CPU_DADDI_WORKAROUNDS))
> + return false;
> /* -imm must be 16 bits */
> return imm >=3D -0x7fff && imm <=3D 0x8000;
> case BPF_AND:
> --=20
> 2.39.2
>=20