[PATCH 1/1] x86/apic: Introduce paravirq irq_domain

[Alexander Popov]

Introduce paravirq irq_domain for interrupts injected by the hypervisor
using Intel VT-x technology. Paravirq irq_domain allows registering
IRQ handlers for these interrupts and avoid emulating an MSI-capable
PCI device by the hypervisor.

Signed-off-by: Alexander Popov <alex.popov@xxxxxxxxx>
---
 arch/x86/Kconfig                 |   8 +++
 arch/x86/include/asm/irqdomain.h |   6 ++
 arch/x86/include/asm/paravirq.h  |   9 +++
 arch/x86/kernel/apic/Makefile    |   2 +
 arch/x86/kernel/apic/paravirq.c  | 128 +++++++++++++++++++++++++++++++++++++++
 arch/x86/kernel/apic/vector.c    |   1 +
 6 files changed, 154 insertions(+)
 create mode 100644 arch/x86/include/asm/paravirq.h
 create mode 100644 arch/x86/kernel/apic/paravirq.c

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 5c6e747..209bd88 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -760,6 +760,14 @@ config PARAVIRT_TIME_ACCOUNTING
 
 	  If in doubt, say N here.
 
+config X86_PARAVIRQ
+	bool "Enable paravirq irq_domain"
+	depends on PARAVIRT && X86_LOCAL_APIC
+	default n
+	---help---
+	  This option enables paravirq irq_domain for interrupts injected
+	  by the hypervisor using Intel VT-x technology.
+
 config PARAVIRT_CLOCK
 	bool
 
diff --git a/arch/x86/include/asm/irqdomain.h b/arch/x86/include/asm/irqdomain.h
index d26075b..e3192f6 100644
--- a/arch/x86/include/asm/irqdomain.h
+++ b/arch/x86/include/asm/irqdomain.h
@@ -60,4 +60,10 @@ extern void arch_init_htirq_domain(struct irq_domain *domain);
 static inline void arch_init_htirq_domain(struct irq_domain *domain) { }
 #endif
 
+#ifdef CONFIG_X86_PARAVIRQ
+extern void arch_init_paravirq_domain(struct irq_domain *domain);
+#else
+static inline void arch_init_paravirq_domain(struct irq_domain *domain) { }
+#endif
+
 #endif
diff --git a/arch/x86/include/asm/paravirq.h b/arch/x86/include/asm/paravirq.h
new file mode 100644
index 0000000..a137de2
--- /dev/null
+++ b/arch/x86/include/asm/paravirq.h
@@ -0,0 +1,9 @@
+#ifndef _ASM_X86_PARAVIRQ_H
+#define _ASM_X86_PARAVIRQ_H
+
+int paravirq_init_chip(void (*irq_mask)(struct irq_data *data),
+				void (*irq_unmask)(struct irq_data *data));
+int paravirq_alloc_irq(void);
+void paravirq_free_irq(unsigned int irq);
+
+#endif /* _ASM_X86_PARAVIRQ_H */
diff --git a/arch/x86/kernel/apic/Makefile b/arch/x86/kernel/apic/Makefile
index 8e63ebd..84f9ce0 100644
--- a/arch/x86/kernel/apic/Makefile
+++ b/arch/x86/kernel/apic/Makefile
@@ -28,3 +28,5 @@ obj-$(CONFIG_X86_BIGSMP)	+= bigsmp_32.o
 
 # For 32bit, probe_32 need to be listed last
 obj-$(CONFIG_X86_LOCAL_APIC)	+= probe_$(BITS).o
+
+obj-$(CONFIG_X86_PARAVIRQ)	+= paravirq.o
diff --git a/arch/x86/kernel/apic/paravirq.c b/arch/x86/kernel/apic/paravirq.c
new file mode 100644
index 0000000..430b819
--- /dev/null
+++ b/arch/x86/kernel/apic/paravirq.c
@@ -0,0 +1,128 @@
+/*
+ * An irq_domain for interrupts injected by the hypervisor using
+ * Intel VT-x technology.
+ *
+ * Copyright (C) 2016 Alexander Popov <alex.popov@xxxxxxxxx>.
+ *
+ * This file is released under the GPLv2.
+ */
+
+#include <linux/init.h>
+#include <linux/irq.h>
+#include <asm/irqdomain.h>
+#include <asm/paravirq.h>
+
+static struct irq_domain *paravirq_domain;
+
+static struct irq_chip paravirq_chip = {
+	.name			= "PARAVIRQ",
+	.irq_ack		= irq_chip_ack_parent,
+};
+
+static int paravirq_domain_alloc(struct irq_domain *domain,
+			unsigned int virq, unsigned int nr_irqs, void *arg)
+{
+	int ret = 0;
+
+	BUG_ON(domain != paravirq_domain);
+
+	if (nr_irqs != 1)
+		return -EINVAL;
+
+	ret = irq_domain_set_hwirq_and_chip(paravirq_domain,
+					virq, virq, &paravirq_chip, NULL);
+	if (ret) {
+		pr_warn("setting chip, hwirq for irq %u failed\n", virq);
+		return ret;
+	}
+
+	__irq_set_handler(virq, handle_edge_irq, 0, "edge");
+
+	return 0;
+}
+
+static void paravirq_domain_free(struct irq_domain *domain,
+					unsigned int virq, unsigned int nr_irqs)
+{
+	struct irq_data *irq_data;
+
+	BUG_ON(domain != paravirq_domain);
+	BUG_ON(nr_irqs != 1);
+
+	irq_data = irq_domain_get_irq_data(paravirq_domain, virq);
+	if (irq_data)
+		irq_domain_reset_irq_data(irq_data);
+	else
+		pr_warn("irq %u is not in paravirq irq_domain\n", virq);
+}
+
+static const struct irq_domain_ops paravirq_domain_ops = {
+	.alloc	= paravirq_domain_alloc,
+	.free	= paravirq_domain_free,
+};
+
+int paravirq_alloc_irq(void)
+{
+	struct irq_alloc_info info;
+
+	if (!paravirq_domain)
+		return -ENODEV;
+
+	if (!paravirq_chip.irq_mask || !paravirq_chip.irq_unmask)
+		return -EINVAL;
+
+	init_irq_alloc_info(&info, NULL);
+
+	return irq_domain_alloc_irqs(paravirq_domain, 1, NUMA_NO_NODE, &info);
+}
+EXPORT_SYMBOL(paravirq_alloc_irq);
+
+void paravirq_free_irq(unsigned int virq)
+{
+	struct irq_data *irq_data;
+
+	if (!paravirq_domain) {
+		pr_warn("paravirq irq_domain is not initialized\n");
+		return;
+	}
+
+	irq_data = irq_domain_get_irq_data(paravirq_domain, virq);
+	if (irq_data)
+		irq_domain_free_irqs(virq, 1);
+	else
+		pr_warn("irq %u is not in paravirq irq_domain\n", virq);
+}
+EXPORT_SYMBOL(paravirq_free_irq);
+
+int paravirq_init_chip(void (*irq_mask)(struct irq_data *data),
+				void (*irq_unmask)(struct irq_data *data))
+{
+	if (!paravirq_domain)
+		return -ENODEV;
+
+	if (paravirq_chip.irq_mask || paravirq_chip.irq_unmask)
+		return -EEXIST;
+
+	if (!irq_mask || !irq_unmask)
+		return -EINVAL;
+
+	paravirq_chip.irq_mask = irq_mask;
+	paravirq_chip.irq_unmask = irq_unmask;
+
+	return 0;
+}
+EXPORT_SYMBOL(paravirq_init_chip);
+
+void arch_init_paravirq_domain(struct irq_domain *parent)
+{
+	paravirq_domain = irq_domain_add_tree(NULL, &paravirq_domain_ops, NULL);
+	if (!paravirq_domain) {
+		pr_warn("failed to initialize paravirq irq_domain\n");
+		return;
+	}
+
+	paravirq_domain->name = paravirq_chip.name;
+	paravirq_domain->parent = parent;
+	paravirq_domain->flags |= IRQ_DOMAIN_FLAG_AUTO_RECURSIVE;
+}
+
diff --git a/arch/x86/kernel/apic/vector.c b/arch/x86/kernel/apic/vector.c
index 6066d94..878b440 100644
--- a/arch/x86/kernel/apic/vector.c
+++ b/arch/x86/kernel/apic/vector.c
@@ -438,6 +438,7 @@ int __init arch_early_irq_init(void)
 
 	arch_init_msi_domain(x86_vector_domain);
 	arch_init_htirq_domain(x86_vector_domain);
+	arch_init_paravirq_domain(x86_vector_domain);
 
 	BUG_ON(!alloc_cpumask_var(&vector_cpumask, GFP_KERNEL));
 	BUG_ON(!alloc_cpumask_var(&vector_searchmask, GFP_KERNEL));
-- 
2.5.5