KVM: arm64: Add helpers to manipulate vcpu flags among a set

Careful analysis of the vcpu flags show that this is a mix of
configuration, communication between the host and the hypervisor,
as well as anciliary state that has no consistency. It'd be a lot
better if we could split these flags into consistent categories.

However, even if we split these flags apart, we want to make sure
that each flag can only be applied to its own set, and not across
sets.

To achieve this, use a preprocessor hack so that each flag is always
associated with:

- the set that contains it,

- a mask that describe all the bits that contain it (for a simple
  flag, this is the same thing as the flag itself, but we will
  eventually have values that cover multiple bits at once).

Each flag is thus a triplet that is not directly usable as a value,
but used by three helpers that allow the flag to be set, cleared,
and fetched. By mandating the use of such helper, we can easily
enforce that a flag can only be used with the set it belongs to.

Finally, one last helper "unpacks" the raw value from the triplet
that represents a flag, which is useful for multi-bit values that
need to be enumerated (in a switch statement, for example).

Further patches will start making use of this infrastructure.
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/include/asm/kvm_host.h

@@ -415,6 +415,50 @@ struct kvm_vcpu_arch {
 	} steal;
 };
 
+/*
+ * Each 'flag' is composed of a comma-separated triplet:
+ *
+ * - the flag-set it belongs to in the vcpu->arch structure
+ * - the value for that flag
+ * - the mask for that flag
+ *
+ *  __vcpu_single_flag() builds such a triplet for a single-bit flag.
+ * unpack_vcpu_flag() extract the flag value from the triplet for
+ * direct use outside of the flag accessors.
+ */
+#define __vcpu_single_flag(_set, _f)	_set, (_f), (_f)
+
+#define __unpack_flag(_set, _f, _m)	_f
+#define unpack_vcpu_flag(...)		__unpack_flag(__VA_ARGS__)
+
+#define __vcpu_get_flag(v, flagset, f, m)			\
+	({							\
+		v->arch.flagset & (m);				\
+	})
+
+#define __vcpu_set_flag(v, flagset, f, m)			\
+	do {							\
+		typeof(v->arch.flagset) *fset;			\
+								\
+		fset = &v->arch.flagset;			\
+		if (HWEIGHT(m) > 1)				\
+			*fset &= ~(m);				\
+		*fset |= (f);					\
+	} while (0)
+
+#define __vcpu_clear_flag(v, flagset, f, m)			\
+	do {							\
+		typeof(v->arch.flagset) *fset;			\
+								\
+		fset = &v->arch.flagset;			\
+		*fset &= ~(m);					\
+	} while (0)
+
+#define vcpu_get_flag(v, ...)	__vcpu_get_flag((v), __VA_ARGS__)
+#define vcpu_set_flag(v, ...)	__vcpu_set_flag((v), __VA_ARGS__)
+#define vcpu_clear_flag(v, ...)	__vcpu_clear_flag((v), __VA_ARGS__)
+
+
 /* Pointer to the vcpu's SVE FFR for sve_{save,load}_state() */
 #define vcpu_sve_pffr(vcpu) (kern_hyp_va((vcpu)->arch.sve_state) +	\
 			     sve_ffr_offset((vcpu)->arch.sve_max_vl))