[PATCH v2 1/3] x86/tdx: Add TDX Guest event notify interrupt support

[Kuppuswamy Sathyanarayanan]

Host-guest event notification via configured interrupt vector is useful
in cases where a guest makes an asynchronous request and needs a
callback from the host to indicate the completion or to let the host
notify the guest about events like device removal. One usage example is,
callback requirement of GetQuote asynchronous hypercall.

In TDX guest, SetupEventNotifyInterrupt hypercall can be used by the
guest to specify which interrupt vector to use as an event-notify
vector from the VMM. Details about the SetupEventNotifyInterrupt
hypercall can be found in TDX Guest-Host Communication Interface
(GHCI) Specification, section "VP.VMCALL<SetupEventNotifyInterrupt>".

As per design, VMM will post the event completion IRQ using the same
CPU on which SetupEventNotifyInterrupt hypercall request is received.
So allocate an IRQ vector from "x86_vector_domain", and set the CPU
affinity of the IRQ vector to the CPU on which
SetupEventNotifyInterrupt hypercall is made.

Add tdx_register_event_irq_cb()/tdx_unregister_event_irq_cb()
interfaces to allow drivers register/unregister event noficiation
handlers.

Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
Reviewed-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Reviewed-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Acked-by: Wander Lairson Costa <wander@xxxxxxxxxx>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
---

Changes since v1:
 * Used early_initcall() instead of arch_initcall() to trigger
   tdx_event_irq_init().
 * Removed unused headers and included headers for spinlock and list
   explicitly.
 * Since during the early_initcall() only one CPU would be enabled, remove
   CPU locking logic (like using set_cpus_allowed_ptr() or get_cpu())

 arch/x86/coco/tdx/tdx.c    | 156 +++++++++++++++++++++++++++++++++++++
 arch/x86/include/asm/tdx.h |   6 ++
 2 files changed, 162 insertions(+)

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 055300e08fb3..26f6e2eaf5c8 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -7,12 +7,17 @@
 #include <linux/cpufeature.h>
 #include <linux/export.h>
 #include <linux/io.h>
+#include <linux/spinlock.h>
+#include <linux/list.h>
+#include <linux/interrupt.h>
+#include <linux/irq.h>
 #include <asm/coco.h>
 #include <asm/tdx.h>
 #include <asm/vmx.h>
 #include <asm/insn.h>
 #include <asm/insn-eval.h>
 #include <asm/pgtable.h>
+#include <asm/irqdomain.h>
 
 /* TDX module Call Leaf IDs */
 #define TDX_GET_INFO			1
@@ -27,6 +32,7 @@
 /* TDX hypercall Leaf IDs */
 #define TDVMCALL_MAP_GPA		0x10001
 #define TDVMCALL_REPORT_FATAL_ERROR	0x10003
+#define TDVMCALL_SETUP_NOTIFY_INTR	0x10004
 
 /* MMIO direction */
 #define EPT_READ	0
@@ -51,6 +57,16 @@
 
 #define TDREPORT_SUBTYPE_0	0
 
+struct event_irq_entry {
+	tdx_event_irq_cb_t handler;
+	void *data;
+	struct list_head head;
+};
+
+static int tdx_event_irq __ro_after_init;
+static LIST_HEAD(event_irq_cb_list);
+static DEFINE_SPINLOCK(event_irq_cb_lock);
+
 /*
  * Wrapper for standard use of __tdx_hypercall with no output aside from
  * return code.
@@ -873,3 +889,143 @@ void __init tdx_early_init(void)
 
 	pr_info("Guest detected\n");
 }
+
+static irqreturn_t tdx_event_irq_handler(int irq, void *dev_id)
+{
+	struct event_irq_entry *entry;
+
+	spin_lock(&event_irq_cb_lock);
+	list_for_each_entry(entry, &event_irq_cb_list, head) {
+		if (entry->handler)
+			entry->handler(entry->data);
+	}
+	spin_unlock(&event_irq_cb_lock);
+
+	return IRQ_HANDLED;
+}
+
+/* Reserve an IRQ from x86_vector_domain for TD event notification */
+static int __init tdx_event_irq_init(void)
+{
+	struct irq_alloc_info info;
+	struct irq_cfg *cfg;
+	int irq;
+
+	if (!cpu_feature_enabled(X86_FEATURE_TDX_GUEST))
+		return 0;
+
+	init_irq_alloc_info(&info, NULL);
+
+	/*
+	 * Event notification vector will be delivered to the CPU
+	 * in which TDVMCALL_SETUP_NOTIFY_INTR hypercall is requested.
+	 * So set the IRQ affinity to the current CPU (CPU 0).
+	 */
+	info.mask = cpumask_of(0);
+
+	irq = irq_domain_alloc_irqs(x86_vector_domain, 1, cpu_to_node(0), &info);
+	if (irq <= 0) {
+		pr_err("Event notification IRQ allocation failed %d\n", irq);
+		return -EIO;
+	}
+
+	irq_set_handler(irq, handle_edge_irq);
+
+	/* Since the IRQ affinity is set, it cannot be balanced */
+	if (request_irq(irq, tdx_event_irq_handler, IRQF_NOBALANCING,
+			"tdx_event_irq", NULL)) {
+		pr_err("Event notification IRQ request failed\n");
+		goto err_free_domain_irqs;
+	}
+
+	cfg = irq_cfg(irq);
+
+	/*
+	 * Since tdx_event_irq_init() is triggered via early_initcall(),
+	 * it will called before secondary CPUs bringup. Since there is
+	 * only one CPU, it complies with the requirement of executing
+	 * the TDVMCALL_SETUP_NOTIFY_INTR hypercall on the same CPU where
+	 * the IRQ vector is allocated.
+	 *
+	 * Register callback vector address with VMM. More details
+	 * about the ABI can be found in TDX Guest-Host-Communication
+	 * Interface (GHCI), sec titled
+	 * "TDG.VP.VMCALL<SetupEventNotifyInterrupt>".
+	 */
+	if (_tdx_hypercall(TDVMCALL_SETUP_NOTIFY_INTR, cfg->vector, 0, 0, 0)) {
+		pr_err("Event notification hypercall failed\n");
+		goto err_free_irqs;
+	}
+
+	tdx_event_irq = irq;
+
+	return 0;
+
+err_free_irqs:
+	free_irq(irq, NULL);
+err_free_domain_irqs:
+	irq_domain_free_irqs(irq, 1);
+
+	return -EIO;
+}
+early_initcall(tdx_event_irq_init)
+
+/**
+ * tdx_register_event_irq_cb() - Register TDX event IRQ callback handler.
+ * @handler: Address of driver specific event IRQ callback handler. Handler
+ *           will be called in IRQ context and hence cannot sleep.
+ * @data: Context data to be passed to the callback handler.
+ *
+ * Return: 0 on success or standard error code on other failures.
+ */
+int tdx_register_event_irq_cb(tdx_event_irq_cb_t handler, void *data)
+{
+	struct event_irq_entry *entry;
+	unsigned long flags;
+
+	if (tdx_event_irq <= 0)
+		return -EIO;
+
+	entry = kzalloc(sizeof(*entry), GFP_KERNEL);
+	if (!entry)
+		return -ENOMEM;
+
+	entry->data = data;
+	entry->handler = handler;
+
+	spin_lock_irqsave(&event_irq_cb_lock, flags);
+	list_add_tail(&entry->head, &event_irq_cb_list);
+	spin_unlock_irqrestore(&event_irq_cb_lock, flags);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(tdx_register_event_irq_cb);
+
+/**
+ * tdx_unregister_event_irq_cb() - Unregister TDX event IRQ callback handler.
+ * @handler: Address of driver specific event IRQ callback handler.
+ * @data: Context data to be passed to the callback handler.
+ *
+ * Return: 0 on success or -EIO if event IRQ is not allocated.
+ */
+int tdx_unregister_event_irq_cb(tdx_event_irq_cb_t handler, void *data)
+{
+	struct event_irq_entry *entry;
+	unsigned long flags;
+
+	if (tdx_event_irq <= 0)
+		return -EIO;
+
+	spin_lock_irqsave(&event_irq_cb_lock, flags);
+	list_for_each_entry(entry, &event_irq_cb_list, head) {
+		if (entry->handler == handler && entry->data == data) {
+			list_del(&entry->head);
+			kfree(entry);
+			break;
+		}
+	}
+	spin_unlock_irqrestore(&event_irq_cb_lock, flags);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(tdx_unregister_event_irq_cb);
diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index 28d889c9aa16..8807fe1b1f3f 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -53,6 +53,8 @@ struct ve_info {
 
 #ifdef CONFIG_INTEL_TDX_GUEST
 
+typedef int (*tdx_event_irq_cb_t)(void *);
+
 void __init tdx_early_init(void);
 
 /* Used to communicate with the TDX module */
@@ -69,6 +71,10 @@ bool tdx_early_handle_ve(struct pt_regs *regs);
 
 int tdx_mcall_get_report0(u8 *reportdata, u8 *tdreport);
 
+int tdx_register_event_irq_cb(tdx_event_irq_cb_t handler, void *data);
+
+int tdx_unregister_event_irq_cb(tdx_event_irq_cb_t handler, void *data);
+
 #else
 
 static inline void tdx_early_init(void) { };
-- 
2.34.1