x86/uintr: Introduce uintr_wait() syscall

Add a new system call to allow applications to block in the kernel and
wait for user interrupts.

<The current implementation doesn't support waking up from other
blocking system calls like sleep(), read(), epoll(), etc.

uintr_wait() is a placeholder syscall while we decide on that
behaviour.>

When the application makes this syscall the notification vector is
switched to a new kernel vector. Any new SENDUIPI will invoke the kernel
interrupt which is then used to wake up the process.

Currently, the task wait list is global one. To make the implementation
scalable there is a need to move to a distributed per-cpu wait list.

Signed-off-by: Sohil Mehta <[email protected]>

4 files changed, 26 insertions, 1 deletions

diff --git a/arch/x86/include/asm/hardirq.h b/arch/x86/include/asm/hardirq.h
index 279afc01f1ac..a4623fdb65a1 100644
--- a/arch/x86/include/asm/hardirq.h
+++ b/arch/x86/include/asm/hardirq.h
@@ -22,6 +22,7 @@ typedef struct {
 #endif
 #ifdef CONFIG_X86_USER_INTERRUPTS
 	unsigned int uintr_spurious_count;
+	unsigned int uintr_kernel_notifications;
 #endif
 	unsigned int x86_platform_ipis;	/* arch dependent */
 	unsigned int apic_perf_irqs;
diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index 5929a6f9eeee..0ac7ef592283 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -673,6 +673,7 @@ DECLARE_IDTENTRY_SYSVEC(POSTED_INTR_NESTED_VECTOR,	sysvec_kvm_posted_intr_nested
 
 #ifdef CONFIG_X86_USER_INTERRUPTS
 DECLARE_IDTENTRY_SYSVEC(UINTR_NOTIFICATION_VECTOR,	sysvec_uintr_spurious_interrupt);
+DECLARE_IDTENTRY_SYSVEC(UINTR_KERNEL_VECTOR,		sysvec_uintr_kernel_notification);
 #endif
 
 #if IS_ENABLED(CONFIG_HYPERV)
diff --git a/arch/x86/include/asm/irq_vectors.h b/arch/x86/include/asm/irq_vectors.h
index d26faa504931..1d289b3ee0da 100644
--- a/arch/x86/include/asm/irq_vectors.h
+++ b/arch/x86/include/asm/irq_vectors.h
@@ -106,8 +106,9 @@
 
 /* Vector for User interrupt notifications */
 #define UINTR_NOTIFICATION_VECTOR       0xec
+#define UINTR_KERNEL_VECTOR		0xeb
 
-#define LOCAL_TIMER_VECTOR		0xeb
+#define LOCAL_TIMER_VECTOR		0xea
 
 #define NR_VECTORS			 256
 
diff --git a/arch/x86/include/asm/uintr.h b/arch/x86/include/asm/uintr.h
index ef3521dd7fb9..64113ef523ca 100644
--- a/arch/x86/include/asm/uintr.h
+++ b/arch/x86/include/asm/uintr.h
@@ -4,11 +4,29 @@
 
 #ifdef CONFIG_X86_USER_INTERRUPTS
 
+/* User Posted Interrupt Descriptor (UPID) */
+struct uintr_upid {
+	struct {
+		u8 status;	/* bit 0: ON, bit 1: SN, bit 2-7: reserved */
+		u8 reserved1;	/* Reserved */
+		u8 nv;		/* Notification vector */
+		u8 reserved2;	/* Reserved */
+		u32 ndst;	/* Notification destination */
+	} nc __packed;		/* Notification control */
+	u64 puir;		/* Posted user interrupt requests */
+} __aligned(64);
+
+/* UPID Notification control status */
+#define UPID_ON		0x0	/* Outstanding notification */
+#define UPID_SN		0x1	/* Suppressed notification */
+
 struct uintr_upid_ctx {
+	struct list_head node;
 	struct task_struct *task;	/* Receiver task */
 	struct uintr_upid *upid;
 	refcount_t refs;
 	bool receiver_active;		/* Flag for UPID being mapped to a receiver */
+	bool waiting;
 };
 
 struct uintr_receiver_info {
@@ -43,11 +61,15 @@ void uintr_free(struct task_struct *task);
 void switch_uintr_prepare(struct task_struct *prev);
 void switch_uintr_return(void);
 
+int uintr_receiver_wait(void);
+void uintr_wake_up_process(void);
+
 #else /* !CONFIG_X86_USER_INTERRUPTS */
 
 static inline void uintr_free(struct task_struct *task) {}
 static inline void switch_uintr_prepare(struct task_struct *prev) {}
 static inline void switch_uintr_return(void) {}
+static inline void uintr_wake_up_process(void) {}
 
 #endif /* CONFIG_X86_USER_INTERRUPTS */