linux-kernel - [PATCH 1/2] MIPS: ebpf jit: Implement DADDI workarounds

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Message-Id: <20230222161222.11879-2-jiaxun.yang@flygoat.com>
Date:   Wed, 22 Feb 2023 16:12:21 +0000
From:   Jiaxun Yang <jiaxun.yang@...goat.com>
To:     linux-mips@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, tsbogend@...ha.franken.de,
        johan.almbladh@...finetworks.com, paulburton@...nel.org,
        bpf@...r.kernel.org, Jiaxun Yang <jiaxun.yang@...goat.com>
Subject: [PATCH 1/2] MIPS: ebpf jit: Implement DADDI workarounds

For DADDI errata we just workaround by disable immediate operation
for BPF_ADD / BPF_SUB to avoid generation of DADDIU.

All other use cases in JIT won't cause overflow thus they are all safe.

Signed-off-by: Jiaxun Yang <jiaxun.yang@...goat.com>
---
 arch/mips/Kconfig            | 1 -
 arch/mips/net/bpf_jit_comp.c | 8 ++++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 37072e15b263..df0910e3895c 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 b17130d510d4..7110a6687f7a 100644
--- a/arch/mips/net/bpf_jit_comp.c
+++ b/arch/mips/net/bpf_jit_comp.c
@@ -218,9 +218,17 @@ bool valid_alu_i(u8 op, s32 imm)
 		/* All legal eBPF values are valid */
 		return true;
 	case BPF_ADD:
+#ifdef CONFIG_64BIT
+		if (IS_ENABLED(CONFIG_CPU_DADDI_WORKAROUNDS))
+			return false;
+#endif
 		/* imm must be 16 bits */
 		return imm >= -0x8000 && imm <= 0x7fff;
 	case BPF_SUB:
+#ifdef CONFIG_64BIT
+		if (IS_ENABLED(CONFIG_CPU_DADDI_WORKAROUNDS))
+			return false;
+#endif
 		/* -imm must be 16 bits */
 		return imm >= -0x7fff && imm <= 0x8000;
 	case BPF_AND:
-- 
2.37.1 (Apple Git-137.1)