[hyperv] Add support for Hyper-V hypervisor

Add support for detecting and communicating with the Hyper-V
hypervisor.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

10 files changed, 977 insertions, 3 deletions

diff --git a/src/arch/i386/include/bits/hyperv.h b/src/arch/i386/include/bits/hyperv.h
new file mode 100644
index 00000000..28387e7a
--- /dev/null
+++ b/src/arch/i386/include/bits/hyperv.h
@@ -0,0 +1,72 @@
+#ifndef _BITS_HYPERV_H
+#define _BITS_HYPERV_H
+
+/** @file
+ *
+ * Hyper-V interface
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <stddef.h>
+#include <stdint.h>
+#include <ipxe/io.h>
+
+/**
+ * Issue hypercall
+ *
+ * @v hv		Hyper-V hypervisor
+ * @v code		Call code
+ * @v in		Input parameters
+ * @v out		Output parameters
+ * @ret status		Status code
+ */
+static inline __attribute__ (( always_inline )) int
+hv_call ( struct hv_hypervisor *hv, unsigned int code, const void *in,
+	  void *out ) {
+	void *hypercall = hv->hypercall;
+	uint32_t in_phys;
+	uint32_t out_phys;
+	uint32_t discard_ecx;
+	uint32_t discard_edx;
+	uint16_t result;
+
+	in_phys = ( ( __builtin_constant_p ( in ) && ( in == NULL ) )
+		       ? 0 : virt_to_phys ( in ) );
+	out_phys = ( ( __builtin_constant_p ( out ) && ( out == NULL ) )
+		       ? 0 : virt_to_phys ( out ) );
+	__asm__ __volatile__ ( "call *%9"
+			       : "=a" ( result ), "=c" ( discard_ecx ),
+				 "=d" ( discard_edx )
+			       : "d" ( 0 ), "a" ( code ),
+				 "b" ( 0 ), "c" ( in_phys ),
+				 "D" ( 0 ), "S" ( out_phys ),
+				 "m" ( hypercall ) );
+	return result;
+}
+
+/**
+ * Set bit atomically
+ *
+ * @v bits		Bit field
+ * @v bit		Bit to set
+ */
+static inline __attribute__ (( always_inline )) void
+hv_set_bit ( void *bits, unsigned int bit ) {
+	struct {
+		uint32_t dword[ ( bit / 32 ) + 1 ];
+	} *dwords = bits;
+
+	/* Set bit using "lock bts".  Inform compiler that any memory
+	 * from the start of the bit field up to and including the
+	 * dword containing this bit may be modified.  (This is
+	 * overkill but shouldn't matter in practice since we're
+	 * unlikely to subsequently read other bits from the same bit
+	 * field.)
+	 */
+	__asm__ __volatile__ ( "lock bts %1, %0"
+			       : "+m" ( *dwords ) : "Ir" ( bit ) );
+}
+
+#endif /* _BITS_HYPERV_H */
diff --git a/src/arch/x86/Makefile b/src/arch/x86/Makefile
index e555587d..a0fee392 100644
--- a/src/arch/x86/Makefile
+++ b/src/arch/x86/Makefile
@@ -9,6 +9,7 @@ SRCDIRS		+= arch/x86/interface/efi
 SRCDIRS		+= arch/x86/prefix
 SRCDIRS		+= arch/x86/hci/commands
 SRCDIRS		+= arch/x86/drivers/xen
+SRCDIRS		+= arch/x86/drivers/hyperv
 
 # breaks building some of the linux-related objects
 CFLAGS		+= -Ulinux
diff --git a/src/arch/i386/core/pic8259.c b/src/arch/x86/core/pic8259.c
index 0a9ea2e0..0a9ea2e0 100644
--- a/src/arch/i386/core/pic8259.c
+++ b/src/arch/x86/core/pic8259.c
diff --git a/src/arch/x86/drivers/hyperv/hyperv.c b/src/arch/x86/drivers/hyperv/hyperv.c
new file mode 100644
index 00000000..bd68d051
--- /dev/null
+++ b/src/arch/x86/drivers/hyperv/hyperv.c
@@ -0,0 +1,553 @@
+/*
+ * Copyright (C) 2014 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+/** @file
+ *
+ * Hyper-V driver
+ *
+ */
+
+#include <stdlib.h>
+#include <stdarg.h>
+#include <string.h>
+#include <unistd.h>
+#include <assert.h>
+#include <errno.h>
+#include <byteswap.h>
+#include <pic8259.h>
+#include <ipxe/malloc.h>
+#include <ipxe/device.h>
+#include <ipxe/cpuid.h>
+#include <ipxe/msr.h>
+#include <ipxe/hyperv.h>
+#include "hyperv.h"
+
+/** Maximum time to wait for a message response
+ *
+ * This is a policy decision.
+ */
+#define HV_MESSAGE_MAX_WAIT_MS 1000
+
+/**
+ * Convert a Hyper-V status code to an iPXE status code
+ *
+ * @v status		Hyper-V status code
+ * @ret rc		iPXE status code (before negation)
+ */
+#define EHV( status ) EPLATFORM ( EINFO_EPLATFORM, (status) )
+
+/**
+ * Allocate zeroed pages
+ *
+ * @v hv		Hyper-V hypervisor
+ * @v ...		Page addresses to fill in, terminated by NULL
+ * @ret rc		Return status code
+ */
+__attribute__ (( sentinel )) int
+hv_alloc_pages ( struct hv_hypervisor *hv, ... ) {
+	va_list args;
+	void **page;
+	int i;
+
+	/* Allocate and zero pages */
+	va_start ( args, hv );
+	for ( i = 0 ; ( ( page = va_arg ( args, void ** ) ) != NULL ); i++ ) {
+		*page = malloc_dma ( PAGE_SIZE, PAGE_SIZE );
+		if ( ! *page )
+			goto err_alloc;
+		memset ( *page, 0, PAGE_SIZE );
+	}
+	va_end ( args );
+
+	return 0;
+
+ err_alloc:
+	va_end ( args );
+	va_start ( args, hv );
+	for ( ; i >= 0 ; i-- ) {
+		page = va_arg ( args, void ** );
+		free_dma ( *page, PAGE_SIZE );
+	}
+	va_end ( args );
+	return -ENOMEM;
+}
+
+/**
+ * Free pages
+ *
+ * @v hv		Hyper-V hypervisor
+ * @v ...		Page addresses, terminated by NULL
+ */
+__attribute__ (( sentinel )) void
+hv_free_pages ( struct hv_hypervisor *hv, ... ) {
+	va_list args;
+	void *page;
+
+	va_start ( args, hv );
+	while ( ( page = va_arg ( args, void * ) ) != NULL )
+		free_dma ( page, PAGE_SIZE );
+	va_end ( args );
+}
+
+/**
+ * Allocate message buffer
+ *
+ * @v hv		Hyper-V hypervisor
+ * @ret rc		Return status code
+ */
+static int hv_alloc_message ( struct hv_hypervisor *hv ) {
+
+	/* Allocate buffer.  Must be aligned to at least 8 bytes and
+	 * must not cross a page boundary, so align on its own size.
+	 */
+	hv->message = malloc_dma ( sizeof ( *hv->message ),
+				   sizeof ( *hv->message ) );
+	if ( ! hv->message )
+		return -ENOMEM;
+
+	return 0;
+}
+
+/**
+ * Free message buffer
+ *
+ * @v hv		Hyper-V hypervisor
+ */
+static void hv_free_message ( struct hv_hypervisor *hv ) {
+
+	/* Free buffer */
+	free_dma ( hv->message, sizeof ( *hv->message ) );
+}
+
+/**
+ * Check whether or not we are running in Hyper-V
+ *
+ * @v hv		Hyper-V hypervisor
+ * @ret rc		Return status code
+ */
+static int hv_check_hv ( struct hv_hypervisor *hv ) {
+	struct x86_features features;
+	uint32_t interface_id;
+	uint32_t discard_ebx;
+	uint32_t discard_ecx;
+	uint32_t discard_edx;
+
+	/* Check for presence of a hypervisor (not necessarily Hyper-V) */
+	x86_features ( &features );
+	if ( ! ( features.intel.ecx & CPUID_FEATURES_INTEL_ECX_HYPERVISOR ) ) {
+		DBGC ( hv, "HV %p not running in a hypervisor\n", hv );
+		return -ENODEV;
+	}
+
+	/* Check that hypervisor is Hyper-V */
+	cpuid ( HV_CPUID_INTERFACE_ID, &interface_id, &discard_ebx,
+		&discard_ecx, &discard_edx );
+	if ( interface_id != HV_INTERFACE_ID ) {
+		DBGC ( hv, "HV %p not running in Hyper-V (interface ID "
+		       "%#08x)\n", hv, interface_id );
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
+/**
+ * Map hypercall page
+ *
+ * @v hv		Hyper-V hypervisor
+ * @ret rc		Return status code
+ */
+static int hv_map_hypercall ( struct hv_hypervisor *hv ) {
+	union {
+		struct {
+			uint32_t ebx;
+			uint32_t ecx;
+			uint32_t edx;
+		} __attribute__ (( packed ));
+		char text[ 13 /* "bbbbccccdddd" + NUL */ ];
+	} vendor_id;
+	uint32_t build;
+	uint32_t version;
+	uint32_t discard_eax;
+	uint32_t discard_ecx;
+	uint32_t discard_edx;
+	uint64_t guest_os_id;
+	uint64_t hypercall;
+
+	/* Report guest OS identity */
+	guest_os_id = rdmsr ( HV_X64_MSR_GUEST_OS_ID );
+	if ( guest_os_id != 0 ) {
+		DBGC ( hv, "HV %p guest OS ID MSR already set to %#08llx\n",
+		       hv, guest_os_id );
+		return -EBUSY;
+	}
+	guest_os_id = HV_GUEST_OS_ID_IPXE;
+	DBGC2 ( hv, "HV %p guest OS ID MSR is %#08llx\n", hv, guest_os_id );
+	wrmsr ( HV_X64_MSR_GUEST_OS_ID, guest_os_id );
+
+	/* Get hypervisor system identity (for debugging) */
+	cpuid ( HV_CPUID_VENDOR_ID, &discard_eax, &vendor_id.ebx,
+		&vendor_id.ecx, &vendor_id.edx );
+	vendor_id.text[ sizeof ( vendor_id.text ) - 1 ] = '\0';
+	cpuid ( HV_CPUID_HYPERVISOR_ID, &build, &version, &discard_ecx,
+		&discard_edx );
+	DBGC ( hv, "HV %p detected \"%s\" version %d.%d build %d\n", hv,
+	       vendor_id.text, ( version >> 16 ), ( version & 0xffff ), build );
+
+	/* Map hypercall page */
+	hypercall = rdmsr ( HV_X64_MSR_HYPERCALL );
+	hypercall &= ( PAGE_SIZE - 1 );
+	hypercall |= ( virt_to_phys ( hv->hypercall ) | HV_HYPERCALL_ENABLE );
+	DBGC2 ( hv, "HV %p hypercall MSR is %#08llx\n", hv, hypercall );
+	wrmsr ( HV_X64_MSR_HYPERCALL, hypercall );
+
+	return 0;
+}
+
+/**
+ * Unmap hypercall page
+ *
+ * @v hv		Hyper-V hypervisor
+ */
+static void hv_unmap_hypercall ( struct hv_hypervisor *hv ) {
+	uint64_t hypercall;
+	uint64_t guest_os_id;
+
+	/* Unmap the hypercall page */
+	hypercall = rdmsr ( HV_X64_MSR_HYPERCALL );
+	hypercall &= ( ( PAGE_SIZE - 1 ) & ~HV_HYPERCALL_ENABLE );
+	DBGC2 ( hv, "HV %p hypercall MSR is %#08llx\n", hv, hypercall );
+	wrmsr ( HV_X64_MSR_HYPERCALL, hypercall );
+
+	/* Reset the guest OS identity */
+	guest_os_id = 0;
+	DBGC2 ( hv, "HV %p guest OS ID MSR is %#08llx\n", hv, guest_os_id );
+	wrmsr ( HV_X64_MSR_GUEST_OS_ID, guest_os_id );
+}
+
+/**
+ * Map synthetic interrupt controller
+ *
+ * @v hv		Hyper-V hypervisor
+ * @ret rc		Return status code
+ */
+static int hv_map_synic ( struct hv_hypervisor *hv ) {
+	uint64_t simp;
+	uint64_t siefp;
+	uint64_t scontrol;
+
+	/* Map SynIC message page */
+	simp = rdmsr ( HV_X64_MSR_SIMP );
+	simp &= ( PAGE_SIZE - 1 );
+	simp |= ( virt_to_phys ( hv->synic.message ) | HV_SIMP_ENABLE );
+	DBGC2 ( hv, "HV %p SIMP MSR is %#08llx\n", hv, simp );
+	wrmsr ( HV_X64_MSR_SIMP, simp );
+
+	/* Map SynIC event page */
+	siefp = rdmsr ( HV_X64_MSR_SIEFP );
+	siefp &= ( PAGE_SIZE - 1 );
+	siefp |= ( virt_to_phys ( hv->synic.event ) | HV_SIEFP_ENABLE );
+	DBGC2 ( hv, "HV %p SIEFP MSR is %#08llx\n", hv, siefp );
+	wrmsr ( HV_X64_MSR_SIEFP, siefp );
+
+	/* Enable SynIC */
+	scontrol = rdmsr ( HV_X64_MSR_SCONTROL );
+	scontrol |= HV_SCONTROL_ENABLE;
+	DBGC2 ( hv, "HV %p SCONTROL MSR is %#08llx\n", hv, scontrol );
+	wrmsr ( HV_X64_MSR_SCONTROL, scontrol );
+
+	return 0;
+}
+
+/**
+ * Unmap synthetic interrupt controller
+ *
+ * @v hv		Hyper-V hypervisor
+ */
+static void hv_unmap_synic ( struct hv_hypervisor *hv ) {
+	uint64_t scontrol;
+	uint64_t siefp;
+	uint64_t simp;
+
+	/* Disable SynIC */
+	scontrol = rdmsr ( HV_X64_MSR_SCONTROL );
+	scontrol &= ~HV_SCONTROL_ENABLE;
+	DBGC2 ( hv, "HV %p SCONTROL MSR is %#08llx\n", hv, scontrol );
+	wrmsr ( HV_X64_MSR_SCONTROL, scontrol );
+
+	/* Unmap SynIC event page */
+	siefp = rdmsr ( HV_X64_MSR_SIEFP );
+	siefp &= ( ( PAGE_SIZE - 1 ) & ~HV_SIEFP_ENABLE );
+	DBGC2 ( hv, "HV %p SIEFP MSR is %#08llx\n", hv, siefp );
+	wrmsr ( HV_X64_MSR_SIEFP, siefp );
+
+	/* Unmap SynIC message page */
+	simp = rdmsr ( HV_X64_MSR_SIMP );
+	simp &= ( ( PAGE_SIZE - 1 ) & ~HV_SIMP_ENABLE );
+	DBGC2 ( hv, "HV %p SIMP MSR is %#08llx\n", hv, simp );
+	wrmsr ( HV_X64_MSR_SIMP, simp );
+}
+
+/**
+ * Enable synthetic interrupt
+ *
+ * @v hv		Hyper-V hypervisor
+ * @v sintx		Synthetic interrupt number
+ */
+void hv_enable_sint ( struct hv_hypervisor *hv, unsigned int sintx ) {
+	unsigned long msr = HV_X64_MSR_SINT ( sintx );
+	uint64_t sint;
+
+	/* Enable synthetic interrupt
+	 *
+	 * We have to enable the interrupt, otherwise messages will
+	 * not be delivered (even though the documentation implies
+	 * that polling for messages is possible).  We enable AutoEOI
+	 * and hook the interrupt to the obsolete IRQ13 (FPU
+	 * exception) vector, which will be implemented as a no-op.
+	 */
+	sint = rdmsr ( msr );
+	sint &= ~( HV_SINT_MASKED | HV_SINT_VECTOR_MASK );
+	sint |= ( HV_SINT_AUTO_EOI |
+		  HV_SINT_VECTOR ( IRQ_INT ( 13 /* See comment above */ ) ) );
+	DBGC2 ( hv, "HV %p SINT%d MSR is %#08llx\n", hv, sintx, sint );
+	wrmsr ( msr, sint );
+}
+
+/**
+ * Disable synthetic interrupt
+ *
+ * @v hv		Hyper-V hypervisor
+ * @v sintx		Synthetic interrupt number
+ */
+void hv_disable_sint ( struct hv_hypervisor *hv, unsigned int sintx ) {
+	unsigned long msr = HV_X64_MSR_SINT ( sintx );
+	uint64_t sint;
+
+	/* Disable synthetic interrupt */
+	sint = rdmsr ( msr );
+	sint &= ~HV_SINT_AUTO_EOI;
+	sint |= HV_SINT_MASKED;
+	DBGC2 ( hv, "HV %p SINT%d MSR is %#08llx\n", hv, sintx, sint );
+	wrmsr ( msr, sint );
+}
+
+/**
+ * Post message
+ *
+ * @v hv		Hyper-V hypervisor
+ * @v id		Connection ID
+ * @v type		Message type
+ * @v data		Message
+ * @v len		Length of message
+ * @ret rc		Return status code
+ */
+int hv_post_message ( struct hv_hypervisor *hv, unsigned int id,
+		      unsigned int type, const void *data, size_t len ) {
+	struct hv_post_message *msg = &hv->message->posted;
+	int status;
+	int rc;
+
+	/* Sanity check */
+	assert ( len <= sizeof ( msg->data ) );
+
+	/* Construct message */
+	memset ( msg, 0, sizeof ( *msg ) );
+	msg->id = cpu_to_le32 ( id );
+	msg->type = cpu_to_le32 ( type );
+	msg->len = cpu_to_le32 ( len );
+	memcpy ( msg->data, data, len );
+	DBGC2 ( hv, "HV %p connection %d posting message type %#08x:\n",
+		hv, id, type );
+	DBGC2_HDA ( hv, 0, msg->data, len );
+
+	/* Post message */
+	if ( ( status = hv_call ( hv, HV_POST_MESSAGE, msg, NULL ) ) != 0 ) {
+		rc = -EHV ( status );
+		DBGC ( hv, "HV %p could not post message to %#08x: %s\n",
+		       hv, id, strerror ( rc ) );
+		return rc;
+	}
+
+	return 0;
+}
+
+/**
+ * Wait for received message
+ *
+ * @v hv		Hyper-V hypervisor
+ * @v sintx		Synthetic interrupt number
+ * @ret rc		Return status code
+ */
+int hv_wait_for_message ( struct hv_hypervisor *hv, unsigned int sintx ) {
+	struct hv_message *msg = &hv->message->received;
+	struct hv_message *src = &hv->synic.message[sintx];
+	unsigned int retries;
+	size_t len;
+
+	/* Wait for message to arrive */
+	for ( retries = 0 ; retries < HV_MESSAGE_MAX_WAIT_MS ; retries++ ) {
+
+		/* Check for message */
+		if ( src->type ) {
+
+			/* Copy message */
+			memset ( msg, 0, sizeof ( *msg ) );
+			len = src->len;
+			assert ( len <= sizeof ( *msg ) );
+			memcpy ( msg, src,
+				 ( offsetof ( typeof ( *msg ), data ) + len ) );
+			DBGC2 ( hv, "HV %p SINT%d received message type "
+				"%#08x:\n", hv, sintx,
+				le32_to_cpu ( msg->type ) );
+			DBGC2_HDA ( hv, 0, msg->data, len );
+
+			/* Consume message */
+			src->type = 0;
+
+			return 0;
+		}
+
+		/* Trigger message delivery */
+		wrmsr ( HV_X64_MSR_EOM, 0 );
+
+		/* Delay */
+		mdelay ( 1 );
+	}
+
+	DBGC ( hv, "HV %p SINT%d timed out waiting for message\n",
+	       hv, sintx );
+	return -ETIMEDOUT;
+}
+
+/**
+ * Signal event
+ *
+ * @v hv		Hyper-V hypervisor
+ * @v id		Connection ID
+ * @v flag		Flag number
+ * @ret rc		Return status code
+ */
+int hv_signal_event ( struct hv_hypervisor *hv, unsigned int id,
+		      unsigned int flag ) {
+	struct hv_signal_event *event = &hv->message->signalled;
+	int status;
+	int rc;
+
+	/* Construct event */
+	memset ( event, 0, sizeof ( *event ) );
+	event->id = cpu_to_le32 ( id );
+	event->flag = cpu_to_le16 ( flag );
+
+	/* Signal event */
+	if ( ( status = hv_call ( hv, HV_SIGNAL_EVENT, event, NULL ) ) != 0 ) {
+		rc = -EHV ( status );
+		DBGC ( hv, "HV %p could not signal event to %#08x: %s\n",
+		       hv, id, strerror ( rc ) );
+		return rc;
+	}
+
+	return 0;
+}
+
+/**
+ * Probe root device
+ *
+ * @v rootdev		Root device
+ * @ret rc		Return status code
+ */
+static int hv_probe ( struct root_device *rootdev ) {
+	struct hv_hypervisor *hv;
+	int rc;
+
+	/* Allocate and initialise structure */
+	hv = zalloc ( sizeof ( *hv ) );
+	if ( ! hv ) {
+		rc = -ENOMEM;
+		goto err_alloc;
+	}
+
+	/* Check we are running in Hyper-V */
+	if ( ( rc = hv_check_hv ( hv ) ) != 0 )
+		goto err_check_hv;
+
+	/* Allocate pages */
+	if ( ( rc = hv_alloc_pages ( hv, &hv->hypercall, &hv->synic.message,
+				     &hv->synic.event, NULL ) ) != 0 )
+		goto err_alloc_pages;
+
+	/* Allocate message buffer */
+	if ( ( rc = hv_alloc_message ( hv ) ) != 0 )
+		goto err_alloc_message;
+
+	/* Map hypercall page */
+	if ( ( rc = hv_map_hypercall ( hv ) ) != 0 )
+		goto err_map_hypercall;
+
+	/* Map synthetic interrupt controller */
+	if ( ( rc = hv_map_synic ( hv ) ) != 0 )
+		goto err_map_synic;
+
+	rootdev_set_drvdata ( rootdev, hv );
+	return 0;
+
+	hv_unmap_synic ( hv );
+ err_map_synic:
+	hv_unmap_hypercall ( hv );
+ err_map_hypercall:
+	hv_free_message ( hv );
+ err_alloc_message:
+	hv_free_pages ( hv, hv->hypercall, hv->synic.message, hv->synic.event,
+			NULL );
+ err_alloc_pages:
+ err_check_hv:
+	free ( hv );
+ err_alloc:
+	return rc;
+}
+
+/**
+ * Remove root device
+ *
+ * @v rootdev		Root device
+ */
+static void hv_remove ( struct root_device *rootdev ) {
+	struct hv_hypervisor *hv = rootdev_get_drvdata ( rootdev );
+
+	hv_unmap_synic ( hv );
+	hv_unmap_hypercall ( hv );
+	hv_free_message ( hv );
+	hv_free_pages ( hv, hv->hypercall, hv->synic.message, hv->synic.event,
+			NULL );
+	free ( hv );
+}
+
+/** Hyper-V root device driver */
+static struct root_driver hv_root_driver = {
+	.probe = hv_probe,
+	.remove = hv_remove,
+};
+
+/** Hyper-V root device */
+struct root_device hv_root_device __root_device = {
+	.dev = { .name = "Hyper-V" },
+	.driver = &hv_root_driver,
+};
diff --git a/src/arch/x86/drivers/hyperv/hyperv.h b/src/arch/x86/drivers/hyperv/hyperv.h
new file mode 100644
index 00000000..94bdb8a8
--- /dev/null
+++ b/src/arch/x86/drivers/hyperv/hyperv.h
@@ -0,0 +1,42 @@
+#ifndef _HYPERV_H
+#define _HYPERV_H
+
+/** @file
+ *
+ * Hyper-V driver
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+/** Get vendor identification */
+#define HV_CPUID_VENDOR_ID 0x40000000UL
+
+/** Get interface identification */
+#define HV_CPUID_INTERFACE_ID 0x40000001UL
+
+/** Get hypervisor identification */
+#define HV_CPUID_HYPERVISOR_ID 0x40000002UL
+
+/** Guest OS identity MSR */
+#define HV_X64_MSR_GUEST_OS_ID 0x40000000UL
+
+/** Hypercall page MSR */
+#define HV_X64_MSR_HYPERCALL 0x40000001UL
+
+/** SynIC control MSR */
+#define HV_X64_MSR_SCONTROL 0x40000080UL
+
+/** SynIC event flags page MSR */
+#define HV_X64_MSR_SIEFP 0x40000082UL
+
+/** SynIC message page MSR */
+#define HV_X64_MSR_SIMP 0x40000083UL
+
+/** SynIC end of message MSR */
+#define HV_X64_MSR_EOM 0x40000084UL
+
+/** SynIC interrupt source MSRs */
+#define HV_X64_MSR_SINT(x) ( 0x40000090UL + (x) )
+
+#endif /* _HYPERV_H */
diff --git a/src/arch/x86/include/bits/errfile.h b/src/arch/x86/include/bits/errfile.h
index 62457562..5fce86af 100644
--- a/src/arch/x86/include/bits/errfile.h
+++ b/src/arch/x86/include/bits/errfile.h
@@ -46,6 +46,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #define ERRFILE_timer_rdtsc   ( ERRFILE_ARCH | ERRFILE_DRIVER | 0x00000000 )
 #define ERRFILE_timer_bios    ( ERRFILE_ARCH | ERRFILE_DRIVER | 0x00010000 )
 #define ERRFILE_hvm	      ( ERRFILE_ARCH | ERRFILE_DRIVER | 0x00020000 )
+#define ERRFILE_hyperv	      ( ERRFILE_ARCH | ERRFILE_DRIVER | 0x00030000 )
 
 #define ERRFILE_cpuid_cmd      ( ERRFILE_ARCH | ERRFILE_OTHER | 0x00000000 )
 #define ERRFILE_cpuid_settings ( ERRFILE_ARCH | ERRFILE_OTHER | 0x00010000 )
diff --git a/src/arch/x86/include/ipxe/cpuid.h b/src/arch/x86/include/ipxe/cpuid.h
index 2f78dfca..fa3a4bc8 100644
--- a/src/arch/x86/include/ipxe/cpuid.h
+++ b/src/arch/x86/include/ipxe/cpuid.h
@@ -39,6 +39,9 @@ struct x86_features {
 /** Get standard features */
 #define CPUID_FEATURES 0x00000001UL
 
+/** Hypervisor is present */
+#define CPUID_FEATURES_INTEL_ECX_HYPERVISOR 0x80000000UL
+
 /** Get largest extended function */
 #define CPUID_AMD_MAX_FN 0x80000000UL
 
diff --git a/src/arch/i386/include/pic8259.h b/src/arch/x86/include/pic8259.h
index a07e97d3..0d02266d 100644
--- a/src/arch/i386/include/pic8259.h
+++ b/src/arch/x86/include/pic8259.h
@@ -11,9 +11,6 @@ FILE_LICENCE ( GPL2_OR_LATER );
 
 #include <ipxe/io.h>
 
-/* For segoff_t */
-#include "realmode.h"
-
 #define IRQ_PIC_CUTOFF 8
 
 /* 8259 register locations */
diff --git a/src/arch/x86_64/include/bits/hyperv.h b/src/arch/x86_64/include/bits/hyperv.h
new file mode 100644
index 00000000..88a3d559
--- /dev/null
+++ b/src/arch/x86_64/include/bits/hyperv.h
@@ -0,0 +1,75 @@
+#ifndef _BITS_HYPERV_H
+#define _BITS_HYPERV_H
+
+/** @file
+ *
+ * Hyper-V interface
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <stddef.h>
+#include <stdint.h>
+#include <ipxe/io.h>
+
+/**
+ * Issue hypercall
+ *
+ * @v hv		Hyper-V hypervisor
+ * @v code		Call code
+ * @v in		Input parameters
+ * @v out		Output parameters
+ * @ret status		Status code
+ */
+static inline __attribute__ (( always_inline )) int
+hv_call ( struct hv_hypervisor *hv, unsigned int code, const void *in,
+	  void *out ) {
+	void *hypercall = hv->hypercall;
+	register uint64_t rcx asm ( "rcx" );
+	register uint64_t rdx asm ( "rdx" );
+	register uint64_t r8 asm ( "r8" );
+	uint64_t in_phys;
+	uint64_t out_phys;
+	uint16_t result;
+
+	in_phys = ( ( __builtin_constant_p ( in ) && ( in == NULL ) )
+		       ? 0 : virt_to_phys ( in ) );
+	out_phys = ( ( __builtin_constant_p ( out ) && ( out == NULL ) )
+		       ? 0 : virt_to_phys ( out ) );
+	rcx = code;
+	rdx = in_phys;
+	r8 = out_phys;
+	__asm__ __volatile__ ( "call *%4"
+			       : "=a" ( result ), "+r" ( rcx ), "+r" ( rdx ),
+				 "+r" ( r8 )
+			       : "m" ( hypercall )
+			       : "r9", "r10", "r11", "xmm0", "xmm1", "xmm2",
+				 "xmm3", "xmm4", "xmm5" );
+	return result;
+}
+
+/**
+ * Set bit atomically
+ *
+ * @v bits		Bit field
+ * @v bit		Bit to set
+ */
+static inline __attribute__ (( always_inline )) void
+hv_set_bit ( void *bits, unsigned int bit ) {
+	struct {
+		uint64_t qword[ ( bit / 64 ) + 1 ];
+	} *qwords = bits;
+
+	/* Set bit using "lock bts".  Inform compiler that any memory
+	 * from the start of the bit field up to and including the
+	 * qword containing this bit may be modified.  (This is
+	 * overkill but shouldn't matter in practice since we're
+	 * unlikely to subsequently read other bits from the same bit
+	 * field.)
+	 */
+	__asm__ __volatile__ ( "lock bts %1, %0"
+			       : "+m" ( *qwords ) : "Ir" ( bit ) );
+}
+
+#endif /* _BITS_HYPERV_H */
diff --git a/src/include/ipxe/hyperv.h b/src/include/ipxe/hyperv.h
new file mode 100644
index 00000000..10be1ca8
--- /dev/null
+++ b/src/include/ipxe/hyperv.h
@@ -0,0 +1,230 @@
+#ifndef _IPXE_HYPERV_H
+#define _IPXE_HYPERV_H
+
+/** @file
+ *
+ * Hyper-V interface
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <stdint.h>
+#include <ipxe/io.h>
+
+/** Hyper-V interface identification */
+#define HV_INTERFACE_ID 0x31237648 /* "Hv#1" */
+
+/** Guest OS identity for iPXE
+ *
+ * This field comprises:
+ *
+ * Bit  63    : set to 1 to indicate an open source OS
+ * Bits 62:56 : OS Type
+ * Bits 55:48 : OS ID
+ * Bits 47:16 : Version
+ * Bits 15:0  : Build number
+ *
+ * There appears to be no central registry for the "OS Type".  The
+ * specification states that "Linux is 0x100", and the FreeBSD source
+ * states that "FreeBSD is 0x200".  Both of these statements are
+ * actually referring to the combined "OS Type" and "OS ID" field.
+ *
+ * We choose to use 0x98ae: this is generated by setting bit 63 (to
+ * indicate an open source OS) and setting the OS Type+ID equal to the
+ * PnP vendor ID used in romprefix.S.  No version information or build
+ * number is included.
+ */
+#define HV_GUEST_OS_ID_IPXE ( ( 1ULL << 63 ) | ( 0x18aeULL << 48 ) )
+
+/** Enable hypercall page */
+#define HV_HYPERCALL_ENABLE 0x00000001UL
+
+/** Enable SynIC */
+#define HV_SCONTROL_ENABLE 0x00000001UL
+
+/** Enable SynIC event flags */
+#define HV_SIEFP_ENABLE 0x00000001UL
+
+/** Enable SynIC messages */
+#define HV_SIMP_ENABLE 0x00000001UL
+
+/** Perform implicit EOI upon synthetic interrupt delivery */
+#define HV_SINT_AUTO_EOI 0x00020000UL
+
+/** Mask synthetic interrupt */
+#define HV_SINT_MASKED 0x00010000UL
+
+/** Synthetic interrupt vector */
+#define HV_SINT_VECTOR(x) ( (x) << 0 )
+
+/** Synthetic interrupt vector mask */
+#define HV_SINT_VECTOR_MASK HV_SINT_VECTOR ( 0xff )
+
+/** Post message */
+#define HV_POST_MESSAGE 0x005c
+
+/** A posted message
+ *
+ * This is the input parameter list for the HvPostMessage hypercall.
+ */
+struct hv_post_message {
+	/** Connection ID */
+	uint32_t id;
+	/** Padding */
+	uint32_t reserved;
+	/** Type */
+	uint32_t type;
+	/** Length of message */
+	uint32_t len;
+	/** Message */
+	uint8_t data[240];
+} __attribute__ (( packed ));
+
+/** A received message
+ *
+ * This is the HV_MESSAGE structure from the Hypervisor Top-Level
+ * Functional Specification.  The field order given in the
+ * documentation is incorrect.
+ */
+struct hv_message {
+	/** Type */
+	uint32_t type;
+	/** Length of message */
+	uint8_t len;
+	/** Flags */
+	uint8_t flags;
+	/** Padding */
+	uint16_t reserved;
+	/** Origin */
+	uint64_t origin;
+	/** Message */
+	uint8_t data[240];
+} __attribute__ (( packed ));
+
+/** Signal event */
+#define HV_SIGNAL_EVENT 0x005d
+
+/** A signalled event */
+struct hv_signal_event {
+	/** Connection ID */
+	uint32_t id;
+	/** Flag number */
+	uint16_t flag;
+	/** Reserved */
+	uint16_t reserved;
+} __attribute__ (( packed ));
+
+/** A received event */
+struct hv_event {
+	/** Event flags */
+	uint8_t flags[256];
+} __attribute__ (( packed ));
+
+/** A monitor trigger group
+ *
+ * This is the HV_MONITOR_TRIGGER_GROUP structure from the Hypervisor
+ * Top-Level Functional Specification.
+ */
+struct hv_monitor_trigger {
+	/** Pending events */
+	uint32_t pending;
+	/** Armed events */
+	uint32_t armed;
+} __attribute__ (( packed ));
+
+/** A monitor parameter set
+ *
+ * This is the HV_MONITOR_PARAMETER structure from the Hypervisor
+ * Top-Level Functional Specification.
+ */
+struct hv_monitor_parameter {
+	/** Connection ID */
+	uint32_t id;
+	/** Flag number */
+	uint16_t flag;
+	/** Reserved */
+	uint16_t reserved;
+} __attribute__ (( packed ));
+
+/** A monitor page
+ *
+ * This is the HV_MONITOR_PAGE structure from the Hypervisor Top-Level
+ * Functional Specification.
+ */
+struct hv_monitor {
+	/** Flags */
+	uint32_t flags;
+	/** Reserved */
+	uint8_t reserved_a[4];
+	/** Trigger groups */
+	struct hv_monitor_trigger trigger[4];
+	/** Reserved */
+	uint8_t reserved_b[536];
+	/** Latencies */
+	uint16 latency[4][32];
+	/** Reserved */
+	uint8_t reserved_c[256];
+	/** Parameters */
+	struct hv_monitor_parameter param[4][32];
+	/** Reserved */
+	uint8_t reserved_d[1984];
+} __attribute__ (( packed ));
+
+/** A synthetic interrupt controller */
+struct hv_synic {
+	/** Message page */
+	struct hv_message *message;
+	/** Event flag page */
+	struct hv_event *event;
+};
+
+/** A message buffer */
+union hv_message_buffer {
+	/** Posted message */
+	struct hv_post_message posted;
+	/** Received message */
+	struct hv_message received;
+	/** Signalled event */
+	struct hv_signal_event signalled;
+};
+
+/** A Hyper-V hypervisor */
+struct hv_hypervisor {
+	/** Hypercall page */
+	void *hypercall;
+	/** Synthetic interrupt controller (SynIC) */
+	struct hv_synic synic;
+	/** Message buffer */
+	union hv_message_buffer *message;
+};
+
+#include <bits/hyperv.h>
+
+/**
+ * Calculate the number of pages covering an address range
+ *
+ * @v data		Start of data
+ * @v len		Length of data (must be non-zero)
+ * @ret pfn_count	Number of pages covered
+ */
+static inline unsigned int hv_pfn_count ( physaddr_t data, size_t len ) {
+	unsigned int first_pfn = ( data / PAGE_SIZE );
+	unsigned int last_pfn = ( ( data + len - 1 ) / PAGE_SIZE );
+
+	return ( last_pfn - first_pfn + 1 );
+}
+
+extern __attribute__ (( sentinel )) int
+hv_alloc_pages ( struct hv_hypervisor *hv, ... );
+extern __attribute__ (( sentinel )) void
+hv_free_pages ( struct hv_hypervisor *hv, ... );
+extern void hv_enable_sint ( struct hv_hypervisor *hv, unsigned int sintx );
+extern void hv_disable_sint ( struct hv_hypervisor *hv, unsigned int sintx );
+extern int hv_post_message ( struct hv_hypervisor *hv, unsigned int id,
+			     unsigned int type, const void *data, size_t len );
+extern int hv_wait_for_message ( struct hv_hypervisor *hv, unsigned int sintx );
+extern int hv_signal_event ( struct hv_hypervisor *hv, unsigned int id,
+			     unsigned int flag );
+
+#endif /* _IPXE_HYPERV_H */