arm64: KVM: Add ARCH_WORKAROUND_2 support for guests

In order to offer ARCH_WORKAROUND_2 support to guests, we need
a bit of infrastructure.

Let's add a flag indicating whether or not the guest uses
SSBD mitigation. Depending on the state of this flag, allow
KVM to disable ARCH_WORKAROUND_2 before entering the guest,
and enable it when exiting it.

Reviewed-by: Christoffer Dall <christoffer.dall@arm.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/kvm_mmu.h

@@ -456,6 +456,30 @@ static inline int kvm_map_vectors(void)
 }
 #endif
 
+#ifdef CONFIG_ARM64_SSBD
+DECLARE_PER_CPU_READ_MOSTLY(u64, arm64_ssbd_callback_required);
+
+static inline int hyp_map_aux_data(void)
+{
+	int cpu, err;
+
+	for_each_possible_cpu(cpu) {
+		u64 *ptr;
+
+		ptr = per_cpu_ptr(&arm64_ssbd_callback_required, cpu);
+		err = create_hyp_mappings(ptr, ptr + 1, PAGE_HYP);
+		if (err)
+			return err;
+	}
+	return 0;
+}
+#else
+static inline int hyp_map_aux_data(void)
+{
+	return 0;
+}
+#endif
+
 #define kvm_phys_to_vttbr(addr)		phys_to_ttbr(addr)
 
 #endif /* __ASSEMBLY__ */