Convert the event channel fastpath to the "map local" CLASS() APIs, using
the "try" variants as the faspath can't block.

Note!  The vcpu_info mapping is read/write, even though there is no
existing call to mark the page dirty.  Like Xen's shared info page, the
vCPU info page is assumed to be dirty at all times, and so isn't marked
dirty after every write.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/xen.c | 42 ++++++++++++++++--------------------------
 1 file changed, 16 insertions(+), 26 deletions(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 8f822acb11a4..47750316f132 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -1774,29 +1774,28 @@ static void __kvm_xen_set_evtchn_fast(struct kvm_vcpu *vcpu, int port_word_bit)
 	bool kick_vcpu = false;
 
 	/* Now switch to the vCPU's vcpu_info to set the index and pending_sel */
-	if (!read_trylock(&gpc->lock)) {
-		/*
-		 * Could not access the vcpu_info. Set the bit in-kernel and
-		 * prod the vCPU to deliver it for itself.
-		 */
+	CLASS(gpc_try_map_local, vcpu_info_map)(gpc, sizeof(struct vcpu_info));
+
+	/*
+	 * If the vcpu_info is inaccessible, set the bit in-kernel and prod the
+	 * vCPU to deliver it for itself.
+	 */
+	if (IS_ERR(vcpu_info_map)) {
 		if (!test_and_set_bit(port_word_bit, &vcpu->arch.xen.evtchn_pending_sel))
 			kick_vcpu = true;
 		goto out_kick;
 	}
-	if (!kvm_gpc_check(gpc, sizeof(struct vcpu_info))) {
-		if (!test_and_set_bit(port_word_bit, &vcpu->arch.xen.evtchn_pending_sel))
-			kick_vcpu = true;
-		goto out_unlock;
-	}
 
 	if (IS_ENABLED(CONFIG_64BIT) && vcpu->kvm->arch.xen.long_mode) {
-		struct vcpu_info *vcpu_info = gpc->khva;
+		struct vcpu_info *vcpu_info = *vcpu_info_map;
+
 		if (!test_and_set_bit(port_word_bit, &vcpu_info->evtchn_pending_sel)) {
 			WRITE_ONCE(vcpu_info->evtchn_upcall_pending, 1);
 			kick_vcpu = true;
 		}
 	} else {
-		struct compat_vcpu_info *vcpu_info = gpc->khva;
+		struct compat_vcpu_info *vcpu_info = *vcpu_info_map;
+
 		if (!test_and_set_bit(port_word_bit,
 					(unsigned long *)&vcpu_info->evtchn_pending_sel)) {
 			WRITE_ONCE(vcpu_info->evtchn_upcall_pending, 1);
@@ -1810,8 +1809,6 @@ static void __kvm_xen_set_evtchn_fast(struct kvm_vcpu *vcpu, int port_word_bit)
 		kick_vcpu = false;
 	}
 
-out_unlock:
-	read_unlock(&gpc->lock);
 out_kick:
 	if (kick_vcpu) {
 		kvm_make_request(KVM_REQ_UNBLOCK, vcpu);
@@ -1850,23 +1847,19 @@ int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *xe, struct kvm *kvm)
 	if (xe->port >= max_evtchn_port(kvm))
 		return -EINVAL;
 
-	rc = -EWOULDBLOCK;
-
 	guard(srcu)(&kvm->srcu);
 
-	if (!read_trylock(&gpc->lock))
-		return rc;
-
-	if (!kvm_gpc_check(gpc, PAGE_SIZE))
-		goto out_unlock;
+	CLASS(gpc_try_map_local, shinfo_map)(gpc, PAGE_SIZE);
+	if (IS_ERR(shinfo_map))
+		return -EWOULDBLOCK;
 
 	if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode) {
-		struct shared_info *shinfo = gpc->khva;
+		struct shared_info *shinfo = *shinfo_map;
 		pending_bits = (unsigned long *)&shinfo->evtchn_pending;
 		mask_bits = (unsigned long *)&shinfo->evtchn_mask;
 		port_word_bit = xe->port / 64;
 	} else {
-		struct compat_shared_info *shinfo = gpc->khva;
+		struct compat_shared_info *shinfo = *shinfo_map;
 		pending_bits = (unsigned long *)&shinfo->evtchn_pending;
 		mask_bits = (unsigned long *)&shinfo->evtchn_mask;
 		port_word_bit = xe->port / 32;
@@ -1888,9 +1881,6 @@ int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *xe, struct kvm *kvm)
 		rc = 1; /* Delivered to the bitmap in shared_info. */
 	}
 
-out_unlock:
-	read_unlock(&gpc->lock);
-
 	if (rc == 1)
 		__kvm_xen_set_evtchn_fast(vcpu, port_word_bit);
 	return rc;
-- 
2.54.0.823.g6e5bcc1fc9-goog