RE: [PATCH v3 2/2] xen/arm: Throw messages for unknown FP/SIMD implement ID

[Wei Chen <Wei.Chen@xxxxxxx>]

Hi Julien,

> -----Original Message-----
> From: Julien Grall <julien@xxxxxxx>
> Sent: 2020年8月25日 19:18
> To: Wei Chen <Wei.Chen@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx;
> sstabellini@xxxxxxxxxx
> Cc: Andre Przywara <Andre.Przywara@xxxxxxx>; Bertrand Marquis
> <Bertrand.Marquis@xxxxxxx>; Penny Zheng <Penny.Zheng@xxxxxxx>; Kaly
> Xin <Kaly.Xin@xxxxxxx>; nd <nd@xxxxxxx>
> Subject: Re: [PATCH v3 2/2] xen/arm: Throw messages for unknown FP/SIMD
> implement ID
> 
> Hi,
> 
> On 25/08/2020 11:08, Wei Chen wrote:
> > Arm ID_AA64PFR0_EL1 register provides two fields to describe CPU
> > FP/SIMD implementations. Currently, we exactly know the meaning of
> > 0x0, 0x1 and 0xf of these fields. Xen treats value < 8 as FP/SIMD
> > features presented. If there is a value 0x2 bumped in the future,
> > Xen behaviors for value <= 0x1 can also take effect. But what Xen
> > done for value <= 0x1 may not always cover new value 0x2 required.
> > We throw these messages to break the silence when Xen detected
> > unknown FP/SIMD IDs to notice user to check.
> >
> > Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
> > Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
> 
> OOI, is this reviewed-by coming from internal review?

Ahh. No, I remember Bertrand gave me a reviewed-by in v2, so I picked it.
I had left OSS for a while, and forgot something. If I can't pick it directly, 
could
you please tell me how can I handle such reviewed-by?

> 
> > ---
> >   xen/arch/arm/setup.c             | 12 ++++++++++++
> >   xen/include/asm-arm/cpufeature.h |  2 ++
> >   2 files changed, 14 insertions(+)
> >
> > diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
> > index 7968cee47d..ef39ce1ec6 100644
> > --- a/xen/arch/arm/setup.c
> > +++ b/xen/arch/arm/setup.c
> > @@ -133,6 +133,18 @@ static void __init processor_id(void)
> >              cpu_has_simd ? " AdvancedSIMD" : "",
> >              cpu_has_gicv3 ? " GICv3-SysReg" : "");
> >
> > +    /* Warn user if we find unknown floating-point features */
> > +    if ( cpu_has_unknown_fp )
> > +        printk(XENLOG_WARNING "WARNING: Unknown Floating-point ID:%d, "
> > +               "this may result to corruption on the platform\n",
> > +               boot_cpu_feature64(fp));
> > +
> > +    /* Warn user if we find unknown AdvancedSIMD features */
> > +    if ( cpu_has_unknown_simd )
> > +        printk(XENLOG_WARNING "WARNING: Unknown AdvancedSIMD ID:%d,
> "
> > +               "this may result to corruption on the platform\n",
> > +               boot_cpu_feature64(simd));
> > +
> >       printk("  Debug Features: %016"PRIx64" %016"PRIx64"\n",
> >              boot_cpu_data.dbg64.bits[0], boot_cpu_data.dbg64.bits[1]);
> >       printk("  Auxiliary Features: %016"PRIx64" %016"PRIx64"\n",
> > diff --git a/xen/include/asm-arm/cpufeature.h b/xen/include/asm-
> arm/cpufeature.h
> > index 10878ead8a..a32309986e 100644
> > --- a/xen/include/asm-arm/cpufeature.h
> > +++ b/xen/include/asm-arm/cpufeature.h
> > @@ -16,6 +16,8 @@
> >   #define cpu_has_fp        (boot_cpu_feature64(fp) < 8)
> >   #define cpu_has_simd      (boot_cpu_feature64(simd) < 8)
> >   #define cpu_has_gicv3     (boot_cpu_feature64(gic) == 1)
> > +#define cpu_has_unknown_fp   (cpu_has_fp && (boot_cpu_feature64(fp) >=
> 2))
> > +#define cpu_has_unknown_simd (cpu_has_simd &&
> (boot_cpu_feature64(simd) >= 2))
> 
> I would rather prefer if we don't introduce cpu_has_unknown_{fp, simd}
> but open-code directly in the 'if'.
> 
> Other than that the code looks ok to me.

Thanks, I could address it in v4.

> 
> Cheers,
> 
> --
> Julien Grall