x86/vector: Reserve vectors for Hyper-V redirected interrupts

Recent versions of Hyper-V hosts use IOMMU posted interrupts to deliver
the interrupts of VTL0 passthrough devices directly the underlying VTL2
guest. These interrupts are hardware vectors in the VTL2 guest and need
an interrupt gate in the Interrupt Descriptor Table.

Reserve a block of 32 interrupt vectors immediately below the FIRST_
SYSTEM_VECTOR. This can be regarded as an expansion of the system
vectors at the expense of external vectors. This should be acceptable
since not many external vectors are used in the normal operation of the
VTL2 kernel. Moreover, the proxy interrupts that the VTL2 guest handles
come from devices.

Signed-off-by: Ricardo Neri <[email protected]>
---
Changes since v1:
 * None

Author: ricardon

arch/x86/include/asm/irq_vectors.h

@@ -18,7 +18,9 @@
  *  Vectors   0 ...  31 : system traps and exceptions - hardcoded events
  *  Vectors  32 ... 127 : device interrupts
  *  Vector  128         : legacy int80 syscall interface
- *  Vectors 129 ... FIRST_SYSTEM_VECTOR-1 : device interrupts
+ *  Vectors 129 ... FIRST_HV_VTL_REDIRECTED_VECTOR-1: more device interrupts
+ *  Vectors FIRST_HV_VTL_REDIRECTED_VECTOR ... FIRST_SYSTEM_VECTOR-1
+ *                      : HyperV redirected device interrupts
  *  Vectors FIRST_SYSTEM_VECTOR ... 255   : special interrupts
  *
  * 64-bit x86 has per CPU IDT tables, 32-bit has one shared IDT table.
@@ -91,6 +93,7 @@
 #define MANAGED_IRQ_SHUTDOWN_VECTOR	0xef
 
 #if IS_ENABLED(CONFIG_HYPERV)
+#define FIRST_HV_VTL_REDIRECTED_VECTOR	0xcc
 #define HYPERV_REENLIGHTENMENT_VECTOR	0xee
 #define HYPERV_STIMER0_VECTOR		0xed
 #endif
@@ -111,7 +114,12 @@
 #define FIRST_SYSTEM_VECTOR		NR_VECTORS
 #endif
 
+#ifdef CONFIG_HYPERV_VTL_MODE
+#define NR_EXTERNAL_VECTORS		(FIRST_HV_VTL_REDIRECTED_VECTOR - FIRST_EXTERNAL_VECTOR)
+#define NR_HV_VTL_REDIRECTED_VECTORS	(FIRST_SYSTEM_VECTOR - FIRST_HV_VTL_REDIRECTED_VECTOR)
+#else
 #define NR_EXTERNAL_VECTORS		(FIRST_SYSTEM_VECTOR - FIRST_EXTERNAL_VECTOR)
+#endif
 #define NR_SYSTEM_VECTORS		(NR_VECTORS - FIRST_SYSTEM_VECTOR)
 
 /*