Re: [PATCH] target/arm: Advertise Cortex-A53 erratum #843419 fix via REVIDR

[Ard Biesheuvel <ardb@kernel.org>]

On Thu, 15 Feb 2024 at 21:47, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> On 2/15/24 06:02, Ard Biesheuvel wrote:
> > From: Ard Biesheuvel <ardb@kernel.org>
> >
> > The Cortex-A53 r0p4 revision that QEMU emulates is affected by a CatA
> > erratum #843419 (i.e., the most severe), which requires workarounds in
> > the toolchain as well as the OS.
> >
> > Since the emulation is obviously not affected in the same way, we can
> > indicate this via REVIDR bit #8, which on r0p4 has the meaning that no
> > workarounds for erratum #843419 are needed.
> >
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > ---
> >   target/arm/cpu64.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
> > index 8e30a7993e..0f7a44a28f 100644
> > --- a/target/arm/cpu64.c
> > +++ b/target/arm/cpu64.c
> > @@ -663,7 +663,7 @@ static void aarch64_a53_initfn(Object *obj)
> >       set_feature(&cpu->env, ARM_FEATURE_PMU);
> >       cpu->kvm_target = QEMU_KVM_ARM_TARGET_CORTEX_A53;
> >       cpu->midr = 0x410fd034;
> > -    cpu->revidr = 0x00000000;
> > +    cpu->revidr = 0x00000100;
>
> Is it worth indicating all three errata fixes (bits 7-9)?
>

835769 has a build time workaround in the linker which I don't think
we even bother to enable in the kernel build. It is definitely not
something the OS needs to worry about at runtime, so I don't think it
matters.

The other one is a performance related CatC without a workaround, so
that one can be ignored as well.

OTOH, our emulation is affected by neither so setting the REVIDR bits
for them makes sense. But there is simply no software that I am aware
of that will behave differently as a result (as opposed to the one for
843419, which is read by the Linux kernel and triggers workaround
logic in the module loader)

> Anyway,
> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
>

Thanks.