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

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

> On 18 Aug 2020, at 04:11, Wei Chen <Wei.Chen@xxxxxxx> wrote:
> 
> Xen has cpu_has_fp/cpu_has_simd to detect whether the CPU supports
> FP/SIMD or not. But currently, this 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 features, the
> ID_AA64PFR0_EL1.FP/SIMD are 1. For these CPUs, xen will treat them as
> no FP/SIMD support. In this case, the vfp_save/restore_state will not
> take effect.
> 
> Unfortunately, Cortex-N1/A76/A75 are the CPUs support FP/SIMD and
> half-precision floatiing-point. Their ID_AA64PFR0_EL1.FP/SMID are 1
> (see Arm ARM DDI0487F.b, D13.2.64). In this case, on N1/A76/A75
> platforms, Xen will always miss the float pointer registers save/restore.
> If different vCPUs are running on the same pCPU, the float 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>

I tested this patch on an N1SDP and it solving random crashes issues.

Could we consider applying this to 4.14 ?

> ---
> 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..588089e5ae 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) <= 1)
> +#define cpu_has_simd      (boot_cpu_feature64(simd) <= 1)
> #define cpu_has_gicv3     (boot_cpu_feature64(gic) == 1)
> #endif
> 
> -- 
> 2.17.1
>