hyperv: Fix vmbus after the i386 4/4 split

The vmbus ISR needs to live in a trampoline.  Dynamically allocating a
trampoline at driver initialization time poses some difficulties due to
the fact that the KENTER macro assumes that the offset relative to
tramp_idleptd is fixed at static link time.  Another problem is that
native_lapic_ipi_alloc() uses setidt(), which assumes a fixed trampoline
offset.

Rather than fight this, move the Hyper-V ISR to i386/exception.s.  Add a
new HYPERV kernel option to make this optional, and configure it by
default on i386.  This is sufficient to make use of vmbus(4) after the
4/4 split.  Note that vmbus cannot be loaded dynamically and both the
HYPERV option and device must be configured together.  I think this is
not too onerous a requirement, since vmbus(4) was previously
non-functional.

Reported by:	Harry Schmalzbauer <freebsd@omnilan.de>
Tested by:	Harry Schmalzbauer <freebsd@omnilan.de>
Reviewed by:	whu, kib
MFC after:	2 weeks
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D30577

sys/conf/files.i386

@@ -102,7 +102,6 @@ dev/glxiic/glxiic.c		optional glxiic
 dev/glxsb/glxsb.c		optional glxsb
 dev/glxsb/glxsb_hash.c		optional glxsb
 dev/hyperv/vmbus/i386/hyperv_machdep.c			optional	hyperv
-dev/hyperv/vmbus/i386/vmbus_vector.S			optional	hyperv
 dev/le/if_le_isa.c		optional le isa
 dev/nctgpio/nctgpio.c		optional nctgpio
 dev/nfe/if_nfe.c		optional nfe pci

sys/conf/options.i386

@@ -101,6 +101,9 @@ NPX_DEBUG		opt_npx.h
 # BPF just-in-time compiler
 BPF_JITTER		opt_bpf.h
 
+# Hyper-V support
+HYPERV			opt_hyperv.h
+
 XENHVM			opt_global.h
 
 # options for the Intel C600 SAS driver (isci)

sys/dev/hyperv/vmbus/i386/vmbus_vector.S

@@ -35,6 +35,9 @@
 /*
  * This is the Hyper-V vmbus channel direct callback interrupt.
  * Only used when it is running on Hyper-V.
+ *
+ * Note that this file is not compiled directly, it is included into
+ * i386/exception.s.
  */
 	.text
 	SUPERALIGN_TEXT
@@ -45,6 +48,7 @@ IDTVEC(vmbus_isr)
 	cld
 	KENTER
 	pushl	%esp
-	call	vmbus_handle_intr
+	mov	$vmbus_handle_intr, %eax
+	call	*%eax
 	add	$4, %esp
 	jmp	doreti

sys/i386/conf/GENERIC

@@ -339,6 +339,8 @@ device		virtio_scsi		# VirtIO SCSI device
 device		virtio_balloon		# VirtIO Memory Balloon device
 
 # HyperV drivers and enhancement support
+# NOTE: HYPERV depends on hyperv.  They must be added or removed together.
+options 	HYPERV			# Kernel support for HyperV drivers
 device		hyperv			# HyperV drivers
 
 # Xen HVM Guest Optimizations

sys/i386/i386/exception.s

@@ -39,6 +39,7 @@
 #include "opt_apic.h"
 #include "opt_atpic.h"
 #include "opt_hwpmc_hooks.h"
+#include "opt_hyperv.h"
 
 #include "assym.inc"
 
@@ -404,6 +405,14 @@ ENTRY(fork_trampoline)
 
 #ifdef DEV_APIC
 #include <i386/i386/apic_vector.s>
+#endif
+
+#ifdef HYPERV
+	.data
+	.p2align 4
+	.text
+	SUPERALIGN_TEXT
+#include <dev/hyperv/vmbus/i386/vmbus_vector.S>
 #endif
 
 	.data

sys/modules/hyperv/vmbus/Makefile

@@ -13,8 +13,11 @@ SRCS=	hyperv.c \
 	vmbus_et.c \
 	vmbus_if.c \
 	vmbus_res.c \
-	vmbus_vector.S \
 	vmbus_xact.c
+
+.if ${MACHINE_CPUARCH} != "i386"
+SRCS+=	vmbus_vector.S
+.endif
 SRCS+=	acpi_if.h bus_if.h device_if.h opt_acpi.h pci_if.h pcib_if.h vmbus_if.h
 
 # XXX: for assym.inc