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

[Julien Grall <julien@xxxxxxx>]

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?

> ---
>   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.

Cheers,

--
Julien Grall