[PATCH v3 1/2] xen/arm: Missing N1/A76/A75 FP registers in vCPU context switch

[Wei Chen <wei.chen@xxxxxxx>]

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 support, the
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>
---
 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
 
-- 
2.17.1