Drivers: hv: vmbus: Implement Direct Mode for stimer0

The 2016 version of Hyper-V offers the option to operate the guest VM
per-vcpu stimer's in Direct Mode, which means the timer interupts on its
own vector rather than queueing a VMbus message. Direct Mode reduces
timer processing overhead in both the hypervisor and the guest, and
avoids having timer interrupts pollute the VMbus interrupt stream for
the synthetic NIC and storage.  This patch enables Direct Mode by
default on stimer0 when running on a version of Hyper-V that supports
it.

In prep for coming support of Hyper-V on ARM64, the arch independent
portion of the code contains calls to routines that will be populated
on ARM64 but are not needed and do nothing on x86.

Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 40 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 9340f41ce8d3..4488cf0dd499 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -37,6 +37,7 @@ EXPORT_SYMBOL_GPL(ms_hyperv);
 
 #if IS_ENABLED(CONFIG_HYPERV)
 static void (*vmbus_handler)(void);
+static void (*hv_stimer0_handler)(void);
 static void (*hv_kexec_handler)(void);
 static void (*hv_crash_handler)(struct pt_regs *regs);
 
@@ -69,6 +70,41 @@ void hv_remove_vmbus_irq(void)
 EXPORT_SYMBOL_GPL(hv_setup_vmbus_irq);
 EXPORT_SYMBOL_GPL(hv_remove_vmbus_irq);
 
+/*
+ * Routines to do per-architecture handling of stimer0
+ * interrupts when in Direct Mode
+ */
+
+__visible void __irq_entry hv_stimer0_vector_handler(struct pt_regs *regs)
+{
+	struct pt_regs *old_regs = set_irq_regs(regs);
+
+	entering_irq();
+	inc_irq_stat(hyperv_stimer0_count);
+	if (hv_stimer0_handler)
+		hv_stimer0_handler();
+	ack_APIC_irq();
+
+	exiting_irq();
+	set_irq_regs(old_regs);
+}
+
+int hv_setup_stimer0_irq(int *irq, int *vector, void (*handler)(void))
+{
+	*vector = HYPERV_STIMER0_VECTOR;
+	*irq = 0;   /* Unused on x86/x64 */
+	hv_stimer0_handler = handler;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(hv_setup_stimer0_irq);
+
+void hv_remove_stimer0_irq(int irq)
+{
+	/* We have no way to deallocate the interrupt gate */
+	hv_stimer0_handler = NULL;
+}
+EXPORT_SYMBOL_GPL(hv_remove_stimer0_irq);
+
 void hv_setup_kexec_handler(void (*handler)(void))
 {
 	hv_kexec_handler = handler;
@@ -257,6 +293,10 @@ static void __init ms_hyperv_init_platform(void)
 		alloc_intr_gate(HYPERV_REENLIGHTENMENT_VECTOR,
 				hyperv_reenlightenment_vector);
 
+	/* Setup the IDT for stimer0 */
+	if (ms_hyperv.misc_features & HV_X64_STIMER_DIRECT_MODE_AVAILABLE)
+		alloc_intr_gate(HYPERV_STIMER0_VECTOR,
+				hv_stimer0_callback_vector);
 #endif
 }