On Wed, Feb 22, 2023 at 5:12 PM Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx> wrote: > > For DADDI errata we just workaround by disable immediate operation > for BPF_ADD / BPF_SUB to avoid generation of DADDIU. Good, this is an elegant solution to trigger fallback to the register-only operation. Does the DADDI errata only affect the DADDIU, not DADDI? > > All other use cases in JIT won't cause overflow thus they are all safe. There are quite a few other places where DADDIU is emitted. How do you know those are safe? I am interested in your reasoning here, as I don't know what would be safe and not. > > Signed-off-by: Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx> > --- > 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 DADDI/DADDIU are only available on 64-bit CPUs, so the errata would only be applicable to that. No need for the CONFIG_64BIT conditional. > + 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) >
