[PATCH v4 5/5] x86/hyperv: Change interrupt vector for nested root partition

[Jinank Jain]

Traditionally we have been using the HYPERVISOR_CALLBACK_VECTOR to relay
the VMBus interrupt. But this does not work in case of nested
hypervisor. Microsoft Hypervisor reserves 0x31 to 0x34 as the interrupt
vector range for VMBus and thus we have to use one of the vectors from
that range and setup the IDT accordingly.

Signed-off-by: Jinank Jain <jinankjain@xxxxxxxxxxxxxxxxxxx>
---
 arch/x86/include/asm/idtentry.h    |  2 ++
 arch/x86/include/asm/irq_vectors.h |  6 ++++++
 arch/x86/kernel/cpu/mshyperv.c     | 15 +++++++++++++++
 arch/x86/kernel/idt.c              |  9 +++++++++
 drivers/hv/vmbus_drv.c             |  3 ++-
 5 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index 72184b0b2219..c0648e3e4d4a 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -686,6 +686,8 @@ DECLARE_IDTENTRY_SYSVEC(POSTED_INTR_NESTED_VECTOR,	sysvec_kvm_posted_intr_nested
 DECLARE_IDTENTRY_SYSVEC(HYPERVISOR_CALLBACK_VECTOR,	sysvec_hyperv_callback);
 DECLARE_IDTENTRY_SYSVEC(HYPERV_REENLIGHTENMENT_VECTOR,	sysvec_hyperv_reenlightenment);
 DECLARE_IDTENTRY_SYSVEC(HYPERV_STIMER0_VECTOR,	sysvec_hyperv_stimer0);
+DECLARE_IDTENTRY_SYSVEC(HYPERV_INTR_NESTED_VMBUS_VECTOR,
+			sysvec_hyperv_nested_vmbus_intr);
 #endif
 
 #if IS_ENABLED(CONFIG_ACRN_GUEST)
diff --git a/arch/x86/include/asm/irq_vectors.h b/arch/x86/include/asm/irq_vectors.h
index 43dcb9284208..729d19eab7f5 100644
--- a/arch/x86/include/asm/irq_vectors.h
+++ b/arch/x86/include/asm/irq_vectors.h
@@ -102,6 +102,12 @@
 #if IS_ENABLED(CONFIG_HYPERV)
 #define HYPERV_REENLIGHTENMENT_VECTOR	0xee
 #define HYPERV_STIMER0_VECTOR		0xed
+/*
+ * FIXME: Change this, once Microsoft Hypervisor changes its assumption
+ * around VMBus interrupt vector allocation for nested root partition.
+ * Or provides a better interface to detect this instead of hardcoding.
+ */
+#define HYPERV_INTR_NESTED_VMBUS_VECTOR	0x31
 #endif
 
 #define LOCAL_TIMER_VECTOR		0xec
diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 3e6711a6af6b..ec7fef43e03b 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -110,6 +110,21 @@ DEFINE_IDTENTRY_SYSVEC(sysvec_hyperv_callback)
 	set_irq_regs(old_regs);
 }
 
+DEFINE_IDTENTRY_SYSVEC(sysvec_hyperv_nested_vmbus_intr)
+{
+	struct pt_regs *old_regs = set_irq_regs(regs);
+
+	inc_irq_stat(irq_hv_callback_count);
+
+	if (vmbus_handler)
+		vmbus_handler();
+
+	if (ms_hyperv.hints & HV_DEPRECATING_AEOI_RECOMMENDED)
+		ack_APIC_irq();
+
+	set_irq_regs(old_regs);
+}
+
 void hv_setup_vmbus_handler(void (*handler)(void))
 {
 	vmbus_handler = handler;
diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c
index a58c6bc1cd68..ace648856a0b 100644
--- a/arch/x86/kernel/idt.c
+++ b/arch/x86/kernel/idt.c
@@ -160,6 +160,15 @@ static const __initconst struct idt_data apic_idts[] = {
 # endif
 	INTG(SPURIOUS_APIC_VECTOR,		asm_sysvec_spurious_apic_interrupt),
 	INTG(ERROR_APIC_VECTOR,			asm_sysvec_error_interrupt),
+#ifdef CONFIG_HYPERV
+	/*
+	 * This is a hack because we cannot install this interrupt handler via alloc_intr_gate
+	 * as it does not allow interrupt vector less than FIRST_SYSTEM_VECTORS. And hyperv
+	 * does not want anything other than 0x31-0x34 as the interrupt vector for vmbus
+	 * interrupt in case of nested setup.
+	 */
+	INTG(HYPERV_INTR_NESTED_VMBUS_VECTOR, asm_sysvec_hyperv_nested_vmbus_intr),
+#endif
 #endif
 };
 
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 0937877eade9..c1477f3a08dd 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -2767,7 +2767,8 @@ static int __init hv_acpi_init(void)
 	 * normal Linux IRQ mechanism is not used in this case.
 	 */
 #ifdef HYPERVISOR_CALLBACK_VECTOR
-	vmbus_interrupt = HYPERVISOR_CALLBACK_VECTOR;
+	vmbus_interrupt = hv_nested ? HYPERV_INTR_NESTED_VMBUS_VECTOR :
+					    HYPERVISOR_CALLBACK_VECTOR;
 	vmbus_irq = -1;
 #endif
 
-- 
2.25.1