[PATCH v3 02/13] KVM: x86/xen: Introduce kvm_xen_has_64bit_shinfo() macro

[David Woodhouse <dwmw2@infradead.org>]

From: David Woodhouse <dwmw@amazon.co.uk>

Add a kvm_xen_has_64bit_shinfo() helper macro to replace the repeated
pattern of 'IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode'
throughout the Xen emulation code. The macro uses READ_ONCE() to
ensure a consistent snapshot of the flag, which can be changed by
another vCPU at any time.

This is the KVM equivalent of Xen's !has_32bit_shinfo().

Assisted-by: Kiro:claude-opus-4.6-1m
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 arch/x86/kvm/xen.c | 16 ++++++++--------
 arch/x86/kvm/xen.h |  5 +++++
 2 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 8eda3a71462e..b89c973c2730 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -73,7 +73,7 @@ static int kvm_xen_shared_info_init(struct kvm *kvm)
 	BUILD_BUG_ON(offsetof(struct shared_info, wc) != 0xc00);
 	BUILD_BUG_ON(offsetof(struct shared_info, wc_sec_hi) != 0xc0c);
 
-	if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode) {
+	if (kvm_xen_has_64bit_shinfo(kvm)) {
 		struct shared_info *shinfo = gpc->khva;
 
 		wc_sec_hi = &shinfo->wc_sec_hi;
@@ -389,7 +389,7 @@ static void kvm_xen_update_runstate_guest(struct kvm_vcpu *v, bool atomic)
 	BUILD_BUG_ON(sizeof_field(struct vcpu_runstate_info, time) !=
 		     sizeof(vx->runstate_times));
 
-	if (IS_ENABLED(CONFIG_64BIT) && v->kvm->arch.xen.long_mode) {
+	if (kvm_xen_has_64bit_shinfo(v->kvm)) {
 		user_len = sizeof(struct vcpu_runstate_info);
 		times_ofs = offsetof(struct vcpu_runstate_info,
 				     state_entry_time);
@@ -676,7 +676,7 @@ void kvm_xen_inject_pending_events(struct kvm_vcpu *v)
 	}
 
 	/* Now gpc->khva is a valid kernel address for the vcpu_info */
-	if (IS_ENABLED(CONFIG_64BIT) && v->kvm->arch.xen.long_mode) {
+	if (kvm_xen_has_64bit_shinfo(v->kvm)) {
 		struct vcpu_info *vi = gpc->khva;
 
 		asm volatile(LOCK_PREFIX "orq %0, %1\n"
@@ -993,7 +993,7 @@ int kvm_xen_vcpu_set_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
 		 * address, that's actually OK. kvm_xen_update_runstate_guest()
 		 * will cope.
 		 */
-		if (IS_ENABLED(CONFIG_64BIT) && vcpu->kvm->arch.xen.long_mode)
+		if (kvm_xen_has_64bit_shinfo(vcpu->kvm))
 			sz = sizeof(struct vcpu_runstate_info);
 		else
 			sz = sizeof(struct compat_vcpu_runstate_info);
@@ -1441,7 +1441,7 @@ static int kvm_xen_hypercall_complete_userspace(struct kvm_vcpu *vcpu)
 
 static inline int max_evtchn_port(struct kvm *kvm)
 {
-	if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode)
+	if (kvm_xen_has_64bit_shinfo(kvm))
 		return EVTCHN_2L_NR_CHANNELS;
 	else
 		return COMPAT_EVTCHN_2L_NR_CHANNELS;
@@ -1463,7 +1463,7 @@ static bool wait_pending_event(struct kvm_vcpu *vcpu, int nr_ports,
 		goto out_rcu;
 
 	ret = false;
-	if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode) {
+	if (kvm_xen_has_64bit_shinfo(kvm)) {
 		struct shared_info *shinfo = gpc->khva;
 		pending_bits = (unsigned long *)&shinfo->evtchn_pending;
 	} else {
@@ -1844,7 +1844,7 @@ int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *xe, struct kvm *kvm)
 	if (!kvm_gpc_check(gpc, PAGE_SIZE))
 		goto out_rcu;
 
-	if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode) {
+	if (kvm_xen_has_64bit_shinfo(kvm)) {
 		struct shared_info *shinfo = gpc->khva;
 		pending_bits = (unsigned long *)&shinfo->evtchn_pending;
 		mask_bits = (unsigned long *)&shinfo->evtchn_mask;
@@ -1885,7 +1885,7 @@ int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *xe, struct kvm *kvm)
 			goto out_rcu;
 		}
 
-		if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode) {
+		if (kvm_xen_has_64bit_shinfo(kvm)) {
 			struct vcpu_info *vcpu_info = gpc->khva;
 			if (!test_and_set_bit(port_word_bit, &vcpu_info->evtchn_pending_sel)) {
 				WRITE_ONCE(vcpu_info->evtchn_upcall_pending, 1);
diff --git a/arch/x86/kvm/xen.h b/arch/x86/kvm/xen.h
index f372855857a8..9d04e350bdb1 100644
--- a/arch/x86/kvm/xen.h
+++ b/arch/x86/kvm/xen.h
@@ -235,6 +235,11 @@ struct compat_shared_info {
 #define COMPAT_EVTCHN_2L_NR_CHANNELS (8 *				\
 				      sizeof_field(struct compat_shared_info, \
 						   evtchn_pending))
+
+/* Latched VM-wide mode; the KVM equivalent of Xen's !has_32bit_shinfo(). */
+#define kvm_xen_has_64bit_shinfo(kvm) \
+	(IS_ENABLED(CONFIG_64BIT) && READ_ONCE((kvm)->arch.xen.long_mode))
+
 struct compat_vcpu_runstate_info {
     int state;
     uint64_t state_entry_time;
-- 
2.55.0