HV: ioapic: unify the access pattern to RTEs

There are two different ways the current implementation adopts to access ioapic
RTEs:

    1. As two 32-bit registers (typically named ''low'' and ''high''), or

    2. As one 64-bit register (typically named ''rte'').

Two issues arise due to the mixed use of these two patterns.

    1. Additional conversions are introduced. As an example, ioapic_get_rte()
       merges two RTE fragments into a uint64_t, while some callers break it
       back to ''low'' and ''high'' again.

    2. It is tricky to choose the proper width of IOAPIC_RTE_xxx constants. SOS
       boot failure is seen when they are 32-bit due to the following code:

           /* reg is uint64_t */
           vioapic->rtbl[pin].reg &= ~IOAPIC_RTE_REM_IRR;

       while making them 64-bit leads to implicit narrowing when the RTEs are accessed
       in the low & high pattern.

This patch defines a union ''ioapic_rte'' and unifies the access pattern
to IOAPIC and vIOAPIC RTEs.

v1 -> v2:

    * Instead of two 32-bit ''low'' and ''high'', define a union that allows
      either 32-bit or 64-bit accesses to RTEs.

Signed-off-by: Junjie Mao <junjie.mao@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>

hypervisor/include/arch/x86/guest/vioapic.h

@@ -31,6 +31,9 @@
 #ifndef _VIOAPIC_H_
 #define	_VIOAPIC_H_
 
+#include <apicreg.h>
+#include <vm.h>
+
 #define	VIOAPIC_BASE	0xFEC00000UL
 #define	VIOAPIC_SIZE	4096UL
 
@@ -50,7 +53,7 @@ int	vioapic_mmio_read(void *vm, uint64_t gpa,
 
 uint8_t	vioapic_pincount(struct vm *vm);
 void	vioapic_process_eoi(struct vm *vm, uint32_t vector);
-bool	vioapic_get_rte(struct vm *vm, uint8_t pin, void *rte);
+bool	vioapic_get_rte(struct vm *vm, uint8_t pin, union ioapic_rte *rte);
 int	vioapic_mmio_access_handler(struct vcpu *vcpu, struct mem_io *mmio,
 		void *handler_private_data);