Re: [PATCH v2 1/2] xen/arm: Missing N1/A76/A75 FP registers in vCPU context switch

[Julien Grall <julien@xxxxxxx>]

Hi,

On 24/08/2020 04:28, Wei Chen wrote:
> Xen has cpu_has_fp/cpu_has_simd to detect whether the CPU supports
> FP/SIMD or not. But currently, these two MACROs only consider value 0
> of ID_AA64PFR0_EL1.FP/SIMD as FP/SIMD features enabled. But for CPUs
> that support FP/SIMD and half-precision floating-point arithmetic, the
> ID_AA64PFR0_EL1.FP/SIMD are 1 (see Arm ARM DDI0487F.b, D13.2.64).
> For these CPUs, xen will treat them as no FP/SIMD supporti, the
s/supporti/support/

> vfp_save/restore_state will not take effect.
>
>  From the TRM documents of Cortex-A75/A76/N1, we know these CPUs support
> basic Advanced SIMD/FP and half-precision floating-point arithmetic. In
> this case, on N1/A76/A75 platforms, Xen will always miss the floating
> pointer registers save/restore. If different vCPUs are running on the
> same pCPU, the floating pointer registers will be corrupted randomly.
>
> This patch fixes Xen on these new cores.
>
> Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
> Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>

Cheers,

> ---
>   xen/include/asm-arm/cpufeature.h | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/xen/include/asm-arm/cpufeature.h b/xen/include/asm-arm/cpufeature.h
> index 674beb0353..10878ead8a 100644
> --- a/xen/include/asm-arm/cpufeature.h
> +++ b/xen/include/asm-arm/cpufeature.h
> @@ -13,8 +13,8 @@
>   #define cpu_has_el2_64    (boot_cpu_feature64(el2) >= 1)
>   #define cpu_has_el3_32    (boot_cpu_feature64(el3) == 2)
>   #define cpu_has_el3_64    (boot_cpu_feature64(el3) >= 1)
> -#define cpu_has_fp        (boot_cpu_feature64(fp) == 0)
> -#define cpu_has_simd      (boot_cpu_feature64(simd) == 0)
> +#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)
>   #endif
>   
--
Julien Grall