linux-kernel - Re: [PATCH 2/2] MIPS: ebpf jit: Implement R4000 workarounds

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Message-ID: <alpine.DEB.2.21.2302271515100.63909@angie.orcam.me.uk>
Date:   Mon, 27 Feb 2023 15:18:43 +0000 (GMT)
From:   "Maciej W. Rozycki" <macro@...am.me.uk>
To:     Johan Almbladh <johan.almbladh@...finetworks.com>
cc:     Jiaxun Yang <jiaxun.yang@...goat.com>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        linux-kernel@...r.kernel.org,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        "paulburton@...nel.org" <paulburton@...nel.org>,
        bpf@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH 2/2] MIPS: ebpf jit: Implement R4000 workarounds

On Mon, 27 Feb 2023, Johan Almbladh wrote:

> > > R4000 is a 64-bit CPU, so the 32-bit JIT implementation will not be
> > > used. From the Makefile:
> > >
> > > ifeq ($(CONFIG_32BIT),y)
> > >        obj-$(CONFIG_BPF_JIT) += bpf_jit_comp32.o
> > > else
> > >        obj-$(CONFIG_BPF_JIT) += bpf_jit_comp64.o
> > > endif
> >
> > It’s common practice to run 32-bit kernel on R4000 based systems to save some memory :-)
> 
> Ok, I understand.

 Likewise:

	select CPU_R4000_WORKAROUNDS if 64BIT
	select CPU_R4400_WORKAROUNDS if 64BIT

This only applies to 64-bit operations, which are not used in 32-bit code 
(one reason why these early silicon revisions were originally used with 
32-bit software only).

  Maciej