xen: Revert commits da72ff5bfc and 72a9b18629

Recent discussion (http://marc.info/?l=xen-devel&m=149192184523741)
established that commit 72a9b18629 ("xen: Remove event channel
notification through Xen PCI platform device") (and thus commit
da72ff5bfc ("partially revert "xen: Remove event channel
notification through Xen PCI platform device"")) are unnecessary and,
in fact, prevent HVM guests from booting on Xen releases prior to 4.0

Therefore we revert both of those commits.

The summary of that discussion is below:

  Here is the brief summary of the current situation:

  Before the offending commit (72a9b18629):

  1) INTx does not work because of the reset_watches path.
  2) The reset_watches path is only taken if you have Xen > 4.0
  3) The Linux Kernel by default will use vector inject if the hypervisor
     support. So even INTx does not work no body running the kernel with
     Xen > 4.0 would notice. Unless he explicitly disabled this feature
     either in the kernel or in Xen (and this can only be disabled by
     modifying the code, not user-supported way to do it).

  After the offending commit (+ partial revert):

  1) INTx is no longer support for HVM (only for PV guests).
  2) Any HVM guest The kernel will not boot on Xen < 4.0 which does
     not have vector injection support. Since the only other mode
     supported is INTx which.

  So based on this summary, I think before commit (72a9b18629) we were
  in much better position from a user point of view.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>

arch/x86/include/asm/xen/events.h

@@ -20,4 +20,15 @@ static inline int xen_irqs_disabled(struct pt_regs *regs)
 /* No need for a barrier -- XCHG is a barrier on x86. */
 #define xchg_xen_ulong(ptr, val) xchg((ptr), (val))
 
+extern int xen_have_vector_callback;
+
+/*
+ * Events delivered via platform PCI interrupts are always
+ * routed to vcpu 0 and hence cannot be rebound.
+ */
+static inline bool xen_support_evtchn_rebind(void)
+{
+	return (!xen_hvm_domain() || xen_have_vector_callback);
+}
+
 #endif /* _ASM_X86_XEN_EVENTS_H */

arch/x86/pci/xen.c

@@ -447,7 +447,7 @@ void __init xen_msi_init(void)
 
 int __init pci_xen_hvm_init(void)
 {
-	if (!xen_feature(XENFEAT_hvm_pirqs))
+	if (!xen_have_vector_callback || !xen_feature(XENFEAT_hvm_pirqs))
 		return 0;
 
 #ifdef CONFIG_ACPI

arch/x86/xen/enlighten_hvm.c

@@ -18,6 +18,9 @@
 #include "mmu.h"
 #include "smp.h"
 
+__read_mostly int xen_have_vector_callback;
+EXPORT_SYMBOL_GPL(xen_have_vector_callback);
+
 void __ref xen_hvm_init_shared_info(void)
 {
 	int cpu;
@@ -123,7 +126,7 @@ static int xen_cpu_up_prepare_hvm(unsigned int cpu)
 		per_cpu(xen_vcpu_id, cpu) = cpu;
 	xen_vcpu_setup(cpu);
 
-	if (xen_feature(XENFEAT_hvm_safe_pvclock))
+	if (xen_have_vector_callback && xen_feature(XENFEAT_hvm_safe_pvclock))
 		xen_setup_timer(cpu);
 
 	rc = xen_smp_intr_init(cpu);
@@ -139,7 +142,7 @@ static int xen_cpu_dead_hvm(unsigned int cpu)
 {
 	xen_smp_intr_free(cpu);
 
-	if (xen_feature(XENFEAT_hvm_safe_pvclock))
+	if (xen_have_vector_callback && xen_feature(XENFEAT_hvm_safe_pvclock))
 		xen_teardown_timer(cpu);
 
        return 0;
@@ -156,7 +159,8 @@ static void __init xen_hvm_guest_init(void)
 
 	xen_panic_handler_init();
 
-	BUG_ON(!xen_feature(XENFEAT_hvm_callback_vector));
+	if (xen_feature(XENFEAT_hvm_callback_vector))
+		xen_have_vector_callback = 1;
 
 	xen_hvm_smp_init();
 	WARN_ON(xen_cpuhp_setup(xen_cpu_up_prepare_hvm, xen_cpu_dead_hvm));
@@ -189,7 +193,7 @@ bool xen_hvm_need_lapic(void)
 		return false;
 	if (!xen_hvm_domain())
 		return false;
-	if (xen_feature(XENFEAT_hvm_pirqs))
+	if (xen_feature(XENFEAT_hvm_pirqs) && xen_have_vector_callback)
 		return false;
 	return true;
 }

arch/x86/xen/smp_hvm.c

@@ -1,5 +1,7 @@
 #include <asm/smp.h>
 
+#include <xen/events.h>
+
 #include "xen-ops.h"
 #include "smp.h"
 
@@ -49,6 +51,9 @@ static void xen_hvm_cpu_die(unsigned int cpu)
 
 void __init xen_hvm_smp_init(void)
 {
+	if (!xen_have_vector_callback)
+		return;
+
 	smp_ops.smp_prepare_cpus = xen_hvm_smp_prepare_cpus;
 	smp_ops.smp_send_reschedule = xen_smp_send_reschedule;
 	smp_ops.cpu_die = xen_hvm_cpu_die;

arch/x86/xen/time.c

@@ -436,6 +436,14 @@ static void xen_hvm_setup_cpu_clockevents(void)
 
 void __init xen_hvm_init_time_ops(void)
 {
+	/*
+	 * vector callback is needed otherwise we cannot receive interrupts
+	 * on cpu > 0 and at this point we don't know how many cpus are
+	 * available.
+	 */
+	if (!xen_have_vector_callback)
+		return;
+
 	if (!xen_feature(XENFEAT_hvm_safe_pvclock)) {
 		printk(KERN_INFO "Xen doesn't support pvclock on HVM,"
 				"disable pv timer\n");

drivers/xen/events/events_base.c

@@ -1312,6 +1312,9 @@ static int rebind_irq_to_cpu(unsigned irq, unsigned tcpu)
 	if (!VALID_EVTCHN(evtchn))
 		return -1;
 
+	if (!xen_support_evtchn_rebind())
+		return -1;
+
 	/* Send future instances of this interrupt to other vcpu. */
 	bind_vcpu.port = evtchn;
 	bind_vcpu.vcpu = xen_vcpu_nr(tcpu);
@@ -1646,15 +1649,21 @@ void xen_callback_vector(void)
 	int rc;
 	uint64_t callback_via;
 
+	if (xen_have_vector_callback) {
 		callback_via = HVM_CALLBACK_VECTOR(HYPERVISOR_CALLBACK_VECTOR);
 		rc = xen_set_callback_via(callback_via);
-	BUG_ON(rc);
+		if (rc) {
+			pr_err("Request for Xen HVM callback vector failed\n");
+			xen_have_vector_callback = 0;
+			return;
+		}
 		pr_info("Xen HVM callback vector for event delivery is enabled\n");
 		/* in the restore case the vector has already been allocated */
 		if (!test_bit(HYPERVISOR_CALLBACK_VECTOR, used_vectors))
 			alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR,
 					xen_hvm_callback_vector);
 	}
+}
 #else
 void xen_callback_vector(void) {}
 #endif

drivers/xen/platform-pci.c

@@ -90,8 +90,10 @@ static int xen_allocate_irq(struct pci_dev *pdev)
 static int platform_pci_resume(struct pci_dev *pdev)
 {
 	int err;
-	if (!xen_pv_domain())
+
+	if (xen_have_vector_callback)
 		return 0;
+
 	err = xen_set_callback_via(callback_via);
 	if (err) {
 		dev_err(&pdev->dev, "platform_pci_resume failure!\n");
@@ -137,15 +139,7 @@ static int platform_pci_probe(struct pci_dev *pdev,
 
 	platform_mmio = mmio_addr;
 	platform_mmiolen = mmio_len;
-
+	if (!xen_have_vector_callback) {
-	/* 
-	 * Xen HVM guests always use the vector callback mechanism.
-	 * L1 Dom0 in a nested Xen environment is a PV guest inside in an
-	 * HVM environment. It needs the platform-pci driver to get
-	 * notifications from L0 Xen, but it cannot use the vector callback
-	 * as it is not exported by L1 Xen.
-	 */
-	if (xen_pv_domain()) {
 		ret = xen_allocate_irq(pdev);
 		if (ret) {
 			dev_warn(&pdev->dev, "request_irq failed err=%d\n", ret);