Patchwork [v3,4/5] I/O Hook: Override MSRs while triggering MCEs

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Submitter Wang, Rui Y
Date April 15, 2014, 1:48 p.m.
Message ID <1397569691-24691-5-git-send-email-rui.y.wang@intel.com>
Download mbox | patch
Permalink /patch/339289/
State Not Applicable
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Comments

Wang, Rui Y - April 15, 2014, 1:48 p.m.
MSRs can be overriden by specifying a cpu id and an MSR number.

        bash# echo "0:17a-8[4/4]ro" > msr

would override MSR 0x17a on cpu0. Use 'all' as the cpu id to override
the MSR on all CPUs. e.g. "all:17a-8[4/4]ro"

When specifying the interrupt to be triggered, a positive number
denotes an IRQ and a negative number denotes a vector, thus

        bash# echo -18 > irq

specifies that a machine check exception (int 18) will be triggered.

Signed-off-by: Rui Wang <rui.y.wang@intel.com>
---
 Documentation/PCI/iohook.txt |   31 ++++++--
 arch/x86/include/asm/msr.h   |  100 ++++++++++++++++++++-
 arch/x86/lib/msr-smp.c       |   31 +++++++
 drivers/misc/iohook/iohook.c |  195 +++++++++++++++++++++++++++++++++++++++---
 include/linux/reg_ovrd.h     |    1 +
 5 files changed, 335 insertions(+), 23 deletions(-)

Patch

diff --git a/Documentation/PCI/iohook.txt b/Documentation/PCI/iohook.txt
index ae9b4ad..9b3f232 100644
--- a/Documentation/PCI/iohook.txt
+++ b/Documentation/PCI/iohook.txt
@@ -52,11 +52,12 @@  a directory subtree is created under /sys/kernel/debug/iohook
 
 bash# cd /sys/kernel/debug/iohook
 bash# ls
-io  irq  mem  pciconf  trigger
+io  irq  mem  msr pciconf  trigger
 
 Each file is used to manage a type of resource.
 'io' is used to add/show Register Overrides in IO port space.
 'mem' is used to add/show Register Overrides in memory space.
+'msr' is used to add/show Register Overrides in MSR space.
 'pciconf' is used to add/show Register Overrides in pci config space.
 'irq' is used to set the desired IRQ to be triggered via IPI.
 'trigger' is used to turn on/off the I/O Hook.
@@ -74,8 +75,15 @@  for a Register Override in PCI config space, it's specified as:
 
 	domain|bus:dev.func+offset-length[value/mask]attribute
 
+for a Register Override in MSR space, it's specified as:
+
+	cpuid:regnum-length[value/mask]attribute
+
 where
 	address - the 64bit address of the h/w register to be overridden
+	cpuid - the cpu on which the MSR specified by regnum is to be
+		overriden. Use 'all' as the cpuid to specify all cpus.
+	regnum - the MSR to be overriden.
 
 	length - the number of bytes affected. Affected here means that
 		 at least one bit in that byte is overridden. For 'length'
@@ -124,24 +132,35 @@  The syntax is "domain|bus:dev.func+offset-length[value/mask]attribute"
 The first register overrides only bit0 and the second register overrides the
 first 2 bytes (mask == 0xffff), with an initial value of 0x0500.
 
+As another example, MSRs can be overriden by specifying a cpu id and an MSR
+number:
+
+bash# echo "0:17a-8[4/4]ro" > msr
+The above specifies that bit2 of MSR 0x17a on cpu0 is overriden as 1 (bit set).
+
 Register Overrides are disabled when added. They can be enabled by using the
 'trigger' file. See below.
 
 2.3 Add IRQ and enable the Register Overrides
 
-To specify an IRQ to be triggered via IPI, just echo the IRQ number in decimal
-to the 'irq' file. For example:
+To specify an interrupt to be triggered via IPI, just echo the IRQ or vector
+number in decimal to the 'irq' file. A positive number denotes an IRQ and a
+negative number denotes a vector. For example:
 
 bash# cd /sys/kernel/debug/iohook
 bash# echo 9 > irq
 This specifies that IRQ9 be triggered after the Register Overrides are enabled.
 
-To enable the Register Overrides in the kernel:
+bash# echo -18 > irq
+specifies that a machine check exception(vector 18) will be triggered.
+
+Register Overrides are disabled after added. Use the 'trigger' file to enabled
+them all:
 
 bash# echo 1 > trigger
 
-This immediately enables all the Register Overrides and if an IRQ number was
-specified, generate the IPI.
+This immediately enables all the Register Overrides and if an IRQ (or vector)
+number was specified, generate the IPI.
 
 To disable the Register Overrides in the kernel:
 
diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h
index de36f22..cfbfc91 100644
--- a/arch/x86/include/asm/msr.h
+++ b/arch/x86/include/asm/msr.h
@@ -57,7 +57,69 @@  static inline unsigned long long native_read_tscp(unsigned int *aux)
 #define EAX_EDX_RET(val, low, high)	"=A" (val)
 #endif
 
-static inline unsigned long long native_read_msr(unsigned int msr)
+#if !defined(NO_IO_HOOK) && defined(CONFIG_IO_HOOK)
+#ifndef CC_HAVE_ASM_GOTO
+#error "gcc 4.5 feature CC_HAVE_ASM_GOTO is required"
+#endif
+struct static_key;
+#include <asm/jump_label.h>
+#include <linux/reg_ovrd.h>
+
+#define msr_read_ovrd(addr)	\
+{ \
+	u64 val;\
+	if (arch_static_branch(&ovrdhw_enabled)			\
+		&& !read_ovrd_common(OVRD_SPACE_MSR, (u64)addr,	\
+			sizeof(u64), &val, NULL))		\
+			return val;				\
+}
+
+#define msr_read_ovrd_safe(addr, err) \
+{ \
+	u64 val;\
+	if (arch_static_branch(&ovrdhw_enabled)) {		\
+		struct msr_regs_info rv;			\
+		/* Use rv.reg to tell from *_safe_regs() */	\
+		rv.regs = NULL;					\
+		if (!read_ovrd_common(OVRD_SPACE_MSR, (u64)addr,\
+			sizeof(u64), &val, &rv)) {		\
+			*err = rv.err;				\
+			return val;				\
+		}						\
+	}							\
+}
+#define msr_write_ovrd_safe(addr, low, high)			\
+{ \
+	u64 val;\
+	if (arch_static_branch(&ovrdhw_enabled)) {		\
+		struct msr_regs_info rv;			\
+		/* Use rv.reg to tell from *_safe_regs() */	\
+		rv.regs = NULL;					\
+		val = (low) | ((u64)(high) << 32);		\
+		if (!write_ovrd_common(OVRD_SPACE_MSR, addr,	\
+			sizeof(u64), &val, &rv))		\
+			return rv.err;				\
+	}							\
+}
+
+#define msr_write_ovrd(addr, low, high)				\
+{ \
+	u64 val;\
+	if (arch_static_branch(&ovrdhw_enabled)) {		\
+		val = (low) | ((u64)(high) << 32);		\
+		if (!write_ovrd_common(OVRD_SPACE_MSR, addr,	\
+			sizeof(u64), &val, NULL))		\
+			return;					\
+	}							\
+}
+#else /* CONFIG_IO_HOOK */
+#define msr_read_ovrd(addr)
+#define msr_read_ovrd_safe(addr, err)
+#define msr_write_ovrd(addr, low, high)
+#define msr_write_ovrd_safe(addr, low, high)
+#endif /* CONFIG_IO_HOOK */
+
+static inline unsigned long long native_do_read_msr(unsigned int msr)
 {
 	DECLARE_ARGS(val, low, high);
 
@@ -65,7 +127,14 @@  static inline unsigned long long native_read_msr(unsigned int msr)
 	return EAX_EDX_VAL(val, low, high);
 }
 
-static inline unsigned long long native_read_msr_safe(unsigned int msr,
+static inline unsigned long long native_read_msr(unsigned int msr)
+{
+
+	msr_read_ovrd(msr);
+	return native_do_read_msr(msr);
+}
+
+static inline unsigned long long native_do_read_msr_safe(unsigned int msr,
 						      int *err)
 {
 	DECLARE_ARGS(val, low, high);
@@ -81,14 +150,27 @@  static inline unsigned long long native_read_msr_safe(unsigned int msr,
 	return EAX_EDX_VAL(val, low, high);
 }
 
-static inline void native_write_msr(unsigned int msr,
+static inline unsigned long long native_read_msr_safe(unsigned int msr,
+						      int *err)
+{
+	msr_read_ovrd_safe(msr, err);
+	return native_do_read_msr_safe(msr, err);
+}
+
+static inline void native_do_write_msr(unsigned int msr,
 				    unsigned low, unsigned high)
 {
 	asm volatile("wrmsr" : : "c" (msr), "a"(low), "d" (high) : "memory");
 }
 
-/* Can be uninlined because referenced by paravirt */
-notrace static inline int native_write_msr_safe(unsigned int msr,
+static inline void native_write_msr(unsigned int msr,
+				    unsigned low, unsigned high)
+{
+	msr_write_ovrd(msr, low, high);
+	native_do_write_msr(msr, low, high);
+}
+
+static inline int native_do_write_msr_safe(unsigned int msr,
 					unsigned low, unsigned high)
 {
 	int err;
@@ -105,6 +187,14 @@  notrace static inline int native_write_msr_safe(unsigned int msr,
 	return err;
 }
 
+/* Can be uninlined because referenced by paravirt */
+static inline int native_write_msr_safe(unsigned int msr,
+					unsigned low, unsigned high)
+{
+	msr_write_ovrd_safe(msr, low, high);
+	return native_do_write_msr_safe(msr, low, high);
+}
+
 extern unsigned long long native_read_tsc(void);
 
 extern int rdmsr_safe_regs(u32 regs[8]);
diff --git a/arch/x86/lib/msr-smp.c b/arch/x86/lib/msr-smp.c
index 518532e..6a5f177 100644
--- a/arch/x86/lib/msr-smp.c
+++ b/arch/x86/lib/msr-smp.c
@@ -128,6 +128,33 @@  void rdmsr_on_cpus(const struct cpumask *mask, u32 msr_no, struct msr *msrs)
 }
 EXPORT_SYMBOL(rdmsr_on_cpus);
 
+#if !defined(NO_IO_HOOK) && defined(CONFIG_IO_HOOK)
+
+#define rdmsr_safe_regs_ovrd(rv) \
+{ \
+	u64 val;\
+	if (arch_static_branch(&ovrdhw_enabled)) {		\
+		if (!read_ovrd_common(OVRD_SPACE_MSR, 0,	\
+			sizeof(u64), &val, rv))			\
+			return;					\
+	}							\
+}
+
+#define wrmsr_safe_regs_ovrd(rv) \
+{ \
+	u64 val;\
+	if (arch_static_branch(&ovrdhw_enabled)) {		\
+		if (!write_ovrd_common(OVRD_SPACE_MSR, 0,	\
+			sizeof(u64), &val, rv))			\
+			return;					\
+	}							\
+}
+
+#else
+#define rdmsr_safe_regs_ovrd(rv)
+#define wrmsr_safe_regs_ovrd(rv)
+#endif
+
 /*
  * wrmsr on a bunch of CPUs
  *
@@ -229,6 +256,8 @@  static void __rdmsr_safe_regs_on_cpu(void *info)
 {
 	struct msr_regs_info *rv = info;
 
+	rdmsr_safe_regs_ovrd(rv);
+
 	rv->err = rdmsr_safe_regs(rv->regs);
 }
 
@@ -236,6 +265,8 @@  static void __wrmsr_safe_regs_on_cpu(void *info)
 {
 	struct msr_regs_info *rv = info;
 
+	wrmsr_safe_regs_ovrd(rv);
+
 	rv->err = wrmsr_safe_regs(rv->regs);
 }
 
diff --git a/drivers/misc/iohook/iohook.c b/drivers/misc/iohook/iohook.c
index 5584eb7..f81f553 100644
--- a/drivers/misc/iohook/iohook.c
+++ b/drivers/misc/iohook/iohook.c
@@ -22,6 +22,7 @@ 
 #include <asm/hw_irq.h>
 #include <linux/reg_ovrd.h>
 #include <linux/pci.h>
+#include <linux/smp.h>
 #include "iohook.h"
 
 MODULE_LICENSE("GPL");
@@ -35,6 +36,7 @@  static DEFINE_RAW_SPINLOCK(engine_lock);
 LIST_HEAD(ovrd_io_reg_map);
 LIST_HEAD(ovrd_mem_reg_map);
 LIST_HEAD(ovrd_pci_conf_reg_map);
+LIST_HEAD(ovrd_msr_map);
 
 struct static_key ovrdhw_enabled = STATIC_KEY_INIT_FALSE;
 EXPORT_SYMBOL(ovrdhw_enabled);
@@ -52,8 +54,10 @@  struct reg_ovrd *iohook_query_ovrd(int spaceid, int idx)
 		reg_ovrd = &ovrd_mem_reg_map;
 	else if (spaceid == OVRD_SPACE_IO)
 		reg_ovrd = &ovrd_io_reg_map;
-	else
+	else if (spaceid == OVRD_SPACE_PCICONF)
 		reg_ovrd = &ovrd_pci_conf_reg_map;
+	else
+		reg_ovrd = &ovrd_msr_map;
 
 	regentry = NULL;
 	raw_spin_lock_irqsave(&io_hook_lock, lock_flags);
@@ -80,8 +84,10 @@  void iohook_cleanup_ovrd(int spaceid)
 		ovrd_list = &ovrd_mem_reg_map;
 	else if (spaceid == OVRD_SPACE_IO)
 		ovrd_list = &ovrd_io_reg_map;
-	else
+	else if (spaceid == OVRD_SPACE_PCICONF)
 		ovrd_list = &ovrd_pci_conf_reg_map;
+	else
+		ovrd_list = &ovrd_msr_map;
 
 	list_for_each_safe(tmp, next, ovrd_list) {
 		struct reg_ovrd *ovrdreg =
@@ -103,8 +109,10 @@  void iohook_add_ovrd(int spaceid, u64 address, u64 value, u64 mask,
 		reg_ovrd = &ovrd_mem_reg_map;
 	else if (spaceid == OVRD_SPACE_IO)
 		reg_ovrd = &ovrd_io_reg_map;
-	else
+	else if (spaceid == OVRD_SPACE_PCICONF)
 		reg_ovrd = &ovrd_pci_conf_reg_map;
+	else
+		reg_ovrd = &ovrd_msr_map;
 
 	raw_spin_lock_irqsave(&io_hook_lock, lock_flags);
 	list_for_each_entry(ovrdreg, reg_ovrd, node) {
@@ -353,6 +361,20 @@  int read_ovrd_common(int spaceid, u64 address, int len, void *value, void *bus)
 		devfn = PCI_DECODE_DEVFN(address);
 		pos = PCI_DECODE_POS(address);
 		ovrd_list = &ovrd_pci_conf_reg_map;
+	} else if (spaceid == OVRD_SPACE_MSR) {
+		unsigned int cpuid;
+
+		ovrd_list = &ovrd_msr_map;
+		cpuid = smp_processor_id();
+
+		/*
+		 * MSRs are 64bit wide, so x8 to form a contiguous
+		 * address space
+		 */
+		address *= 8;
+
+		/* upper 32bits contain the cpu id */
+		address |= (u64)cpuid << 32;
 	} else {
 		return ret;
 	}
@@ -392,6 +414,29 @@  int read_ovrd_common(int spaceid, u64 address, int len, void *value, void *bus)
 				res = pcib->ops->read(pcib, devfn, pos, len,
 							(u32 *)&data);
 				raw_spin_unlock_irqrestore(&pci_lock, flags);
+			} else if (spaceid == OVRD_SPACE_MSR) {
+				struct msr_regs_info *rv;
+				unsigned int msr;
+
+				rv = (struct msr_regs_info *)bus;
+				msr = address & 0xffffffff;
+				if (rv && rv->regs) { /* rdmsr_safe_regs() */
+					u32 low, high;
+
+					rv->err = rdmsr_safe_regs(rv->regs);
+					low = rv->regs[0]; /* eax */
+					high = rv->regs[2]; /* edx */
+					data = low | ((u64)high << 32);
+					res = rv->err;
+				} else if (rv) { /* rv->regs == NULL */
+					data = native_do_read_msr_safe(msr,
+						&rv->err);
+					res = rv->err;
+				} else { /* rv == NULL */
+					data = native_do_read_msr(msr);
+					res = 0;
+				}
+
 			} else
 				goto out;
 
@@ -486,6 +531,20 @@  int write_ovrd_common(int spaceid, u64 address, int len, void *data, void *bus)
 		devfn = PCI_DECODE_DEVFN(address);
 		pos = PCI_DECODE_POS(address);
 		ovrd_list = &ovrd_pci_conf_reg_map;
+	} else if (spaceid == OVRD_SPACE_MSR) {
+		unsigned int cpuid;
+
+		cpuid = smp_processor_id();
+
+		/*
+		 * MSRs are 64bit wide, so x8 to form a contiguous
+		 * address space
+		 */
+		address *= 8;
+
+		/* upper 32bits contain the cpu id */
+		address |= (u64)cpuid << 32;
+		ovrd_list = &ovrd_msr_map;
 	} else {
 		return ret;
 	}
@@ -525,6 +584,23 @@  int write_ovrd_common(int spaceid, u64 address, int len, void *data, void *bus)
 				raw_spin_unlock_irqrestore(&pci_lock, flags);
 				raw_spin_lock_irqsave(&io_hook_lock,
 					lock_flags);
+			} else if (spaceid == OVRD_SPACE_MSR) {
+				struct msr_regs_info *rv;
+				unsigned int msr, low, high;
+
+				rv = (struct msr_regs_info *)bus;
+				msr = address & 0xffffffff;
+				low = value & 0xffffffff;
+				high = value >> 32;
+
+				if (rv && rv->regs) { /* wrmsr_safe_regs() */
+					rv->err = wrmsr_safe_regs(rv->regs);
+				} else if (rv) { /* rv->regs == NULL */
+					rv->err = native_do_write_msr_safe(msr,
+						low, high);
+				} else { /* rv == NULL */
+					native_do_write_msr(msr, low, high);
+				}
 			} else
 				break;
 		}
@@ -566,12 +642,22 @@  int write_ovrd_common(int spaceid, u64 address, int len, void *data, void *bus)
 }
 EXPORT_SYMBOL(write_ovrd_common);
 
-static void trigger_irq_by_ipi(unsigned long irqnum)
+static void trigger_irq_by_ipi(long irqnum)
 {
 	struct irq_desc *desc;
 	struct irq_data *data;
 	struct irq_chip *chip;
 
+	if (irqnum < 0) { /* vector number */
+		pr_info("sending IPI to vector:%ld\n", -irqnum);
+		if (-irqnum == 18)
+			apic->send_IPI_all(-irqnum);
+		else
+			apic->send_IPI_self(-irqnum);
+		pr_info("Returned from sending IPI to vector:%ld\n", -irqnum);
+		return;
+	}
+
 	desc = irq_to_desc(irqnum);
 	data = irq_desc_get_irq_data(desc);
 	chip = irq_data_get_irq_chip(data);
@@ -637,7 +723,11 @@  ssize_t hook_irq_read(struct file *file, char __user *ubuf, size_t cnt,
 	char buf[64];		/* big enough to hold a number */
 	int r;
 
-	r = sprintf(buf, "%u\n", g_irq_num);
+	if (g_irq_num >= 0)
+		r = sprintf(buf, "irq:%u\n", g_irq_num);
+	else
+		r = sprintf(buf, "vector:%u\n", -g_irq_num);
+
 	return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
 }
 
@@ -645,7 +735,7 @@  static ssize_t hook_irq_write(struct file *file, const char __user *user_buf,
 			size_t count, loff_t *ppos)
 {
 	char *irq = NULL;
-	unsigned long irqnum, ret;
+	long irqnum, ret;
 
 	irq = kmalloc(count+1, GFP_ATOMIC);
 	if (!irq) {
@@ -655,13 +745,19 @@  static ssize_t hook_irq_write(struct file *file, const char __user *user_buf,
 	irq[count] = '\0';
 	if (copy_from_user(irq, user_buf, count))
 		goto end;
-	ret = kstrtoul(irq, 10, &irqnum);
+
+	ret = kstrtol(irq, 10, &irqnum);
 	if (ret) {
-		pr_err("bogus irq number? %s\n", irq);
+		pr_err("bogus irq/vector number? %s\n", irq);
 		goto end;
 	}
-	if (irqnum > NR_IRQS) {
-		pr_err("irq num too big: %lu\n", irqnum);
+
+	/*
+	 * if irqnum < 0 it's a vector number
+	 * if irqnum > 0 it's a IRQ number
+	 */
+	if (irqnum <= -NR_VECTORS || irqnum >= NR_IRQS) {
+		pr_err("irq/vector num too big: %ld\n", irqnum);
 		goto end;
 	}
 
@@ -733,6 +829,13 @@  hook_seq_show(struct seq_file *s, void *it)
 			regmap->address, regmap->length, regmap->val,
 			regmap->bit_mask, hook_attrib(regmap->attrib));
 		break;
+	case OVRD_SPACE_MSR:
+		seq_printf(s,
+			"cpu%d msr: 0x%x length: 0x%x value: 0x%llx mask: 0x%llx attrib: %s\n",
+			(u32)(regmap->address >> 32), (u32)(regmap->address)/8,
+			regmap->length, regmap->val, regmap->bit_mask,
+			hook_attrib(regmap->attrib));
+		break;
 	case OVRD_SPACE_PCICONF:
 		seq_printf(s,
 			"pciconf: 0x%04x|%02x:%02x.%02x offset: 0x%x lenght: 0x%x value: 0x%llx mask: 0x%llx attrib: %s\n",
@@ -772,6 +875,19 @@  hook_io_open(struct inode *inode, struct file *file)
 }
 
 static int
+hook_msr_open(struct inode *inode, struct file *file)
+{
+	struct hook_iter *iter;
+
+	iter = __seq_open_private(file, &hook_seq_ops,
+				sizeof(struct hook_iter));
+	if (iter)
+		iter->spaceid = OVRD_SPACE_MSR;
+
+	return iter ? 0 : -ENOMEM;
+}
+
+static int
 hook_mem_open(struct inode *inode, struct file *file)
 {
 	struct hook_iter *iter;
@@ -817,12 +933,12 @@  hook_parse_entry(char *entry, int spaceid)
 {
 	char *field;
 	u64 address, length, value, mask;
-	unsigned long domain, bus, dev, func;
+	unsigned long domain, bus, dev, func, cpu;
 	int attrib, ret;
 	u16 cval;
 
 	if (spaceid != OVRD_SPACE_PCICONF)
-		goto mem_io;
+		goto msr;
 
 	field = strsep(&entry, "|");
 	ret = kstrtoul(field, 16, &domain);
@@ -843,6 +959,20 @@  hook_parse_entry(char *entry, int spaceid)
 	ret = kstrtoul(field, 16, &func);
 	if (ret || !entry)
 		return -1;
+msr:
+	if (spaceid != OVRD_SPACE_MSR)
+		goto mem_io;
+	field = strsep(&entry, ":");
+	if (strcasecmp(field, "all") == 0) {
+		/* All cpus */
+		cpu = (unsigned long)-1;
+		ret = 0;
+	} else {
+		ret = kstrtoul(field, 16, &cpu);
+	}
+	pr_info("parse_hook_entry() cpu=0x%lx\n", cpu);
+	if (ret || !entry)
+		return -1;
 
 mem_io:
 	field = strsep(&entry, "-");
@@ -850,6 +980,13 @@  mem_io:
 	if (ret || !entry)
 		return -1;
 
+	/*
+	 * MSRs are 64bit wide, so x8 to form a contiguous
+	 * address space
+	 */
+	if (spaceid == OVRD_SPACE_MSR)
+		address *= 8;
+
 	pr_info("parse_hook_entry() address=0x%llx\n", address);
 
 	field = strsep(&entry, "[");
@@ -888,6 +1025,17 @@  mem_io:
 	if (spaceid == OVRD_SPACE_PCICONF) {
 		address = PCI_ENCODE_ADDR(domain, bus, PCI_DEVFN(dev, func),
 			address);
+	} else if (spaceid == OVRD_SPACE_MSR) {
+		if (cpu == (unsigned long)-1) { /* all cpus */
+			for (cpu = 0; cpu < nr_cpu_ids; cpu++) {
+				address &= 0xffffffff;
+				address |= cpu << 32;
+				iohook_add_ovrd(spaceid, address, value, mask,
+					length, attrib);
+			}
+			return 0;
+		}
+		address |= cpu << 32;
 	}
 
 	iohook_add_ovrd(spaceid, address, value, mask, length, attrib);
@@ -945,6 +1093,14 @@  hook_io_write(struct file *file, const char __user *user_buf,
 }
 
 static ssize_t
+hook_msr_write(struct file *file, const char __user *user_buf,
+		 size_t user_len, loff_t *offset)
+{
+
+	return hook_write(file, user_buf, user_len, offset, OVRD_SPACE_MSR);
+}
+
+static ssize_t
 hook_mem_write(struct file *file, const char __user *user_buf,
 		 size_t user_len, loff_t *offset)
 {
@@ -968,6 +1124,14 @@  static const struct file_operations hook_io_fops = {
 	.write = hook_io_write,
 };
 
+static const struct file_operations hook_msr_fops = {
+	.open = hook_msr_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = seq_release_private,
+	.write = hook_msr_write,
+};
+
 static const struct file_operations hook_mem_fops = {
 	.open = hook_mem_open,
 	.read = seq_read,
@@ -1007,11 +1171,18 @@  static int __init iohook_init(void)
 	if (hook_irq_dentry == NULL)
 		return -ENODEV;
 
+#ifdef CONFIG_X86
 	hook_reg_dentry = debugfs_create_file("io", S_IWUSR,
 				root, NULL, &hook_io_fops);
 	if (hook_reg_dentry == NULL)
 		return -ENODEV;
 
+	hook_reg_dentry = debugfs_create_file("msr", S_IWUSR,
+				root, NULL, &hook_msr_fops);
+	if (hook_reg_dentry == NULL)
+		return -ENODEV;
+#endif
+
 	hook_reg_dentry = debugfs_create_file("mem", S_IWUSR,
 				root, NULL, &hook_mem_fops);
 	if (hook_reg_dentry == NULL)
diff --git a/include/linux/reg_ovrd.h b/include/linux/reg_ovrd.h
index 2707d6c..ce655fe 100644
--- a/include/linux/reg_ovrd.h
+++ b/include/linux/reg_ovrd.h
@@ -37,6 +37,7 @@  struct reg_ovrd {
 #define	OVRD_SPACE_IO		0
 #define	OVRD_SPACE_MEM		1
 #define	OVRD_SPACE_PCICONF	2
+#define	OVRD_SPACE_MSR		3
 
 #define	PCI_ENCODE_ADDR(domain, bus, devfn, pos)	\
 		(((u64)(domain))<<32|(bus)<<20|(devfn)<<12|(pos))