enlighten_pv.c

/*
 * Core of Xen paravirt_ops implementation.
 *
 * This file contains the xen_paravirt_ops structure itself, and the
 * implementations for:
 * - privileged instructions
 * - interrupt flags
 * - segment operations
 * - booting and setup
 *
 * Jeremy Fitzhardinge <jeremy@xensource.com>, XenSource Inc, 2007
 */

#include <linux/cpu.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/smp.h>
#include <linux/preempt.h>
#include <linux/hardirq.h>
#include <linux/percpu.h>
#include <linux/delay.h>
#include <linux/start_kernel.h>
#include <linux/sched.h>
#include <linux/kprobes.h>
#include <linux/bootmem.h>
#include <linux/export.h>
#include <linux/mm.h>
#include <linux/page-flags.h>
#include <linux/highmem.h>
#include <linux/console.h>
#include <linux/pci.h>
#include <linux/gfp.h>
#include <linux/memblock.h>
#include <linux/edd.h>
#include <linux/frame.h>

#include <xen/xen.h>
#include <xen/events.h>
#include <xen/interface/xen.h>
#include <xen/interface/version.h>
#include <xen/interface/physdev.h>
#include <xen/interface/vcpu.h>
#include <xen/interface/memory.h>
#include <xen/interface/nmi.h>
#include <xen/interface/xen-mca.h>
#include <xen/features.h>
#include <xen/page.h>
#include <xen/hvc-console.h>
#include <xen/acpi.h>

#include <asm/paravirt.h>
#include <asm/apic.h>
#include <asm/page.h>
#include <asm/xen/pci.h>
#include <asm/xen/hypercall.h>
#include <asm/xen/hypervisor.h>
#include <asm/xen/cpuid.h>
#include <asm/fixmap.h>
#include <asm/processor.h>
#include <asm/proto.h>
#include <asm/msr-index.h>
#include <asm/traps.h>
#include <asm/setup.h>
#include <asm/desc.h>
#include <asm/pgalloc.h>
#include <asm/pgtable.h>
#include <asm/tlbflush.h>
#include <asm/reboot.h>
#include <asm/stackprotector.h>
#include <asm/hypervisor.h>
#include <asm/mach_traps.h>
#include <asm/mwait.h>
#include <asm/pci_x86.h>
#include <asm/cpu.h>

#ifdef CONFIG_ACPI
#include <linux/acpi.h>
#include <asm/acpi.h>
#include <acpi/pdc_intel.h>
#include <acpi/processor.h>
#include <xen/interface/platform.h>
#endif

#include "xen-ops.h"
#include "mmu.h"
#include "smp.h"
#include "multicalls.h"
#include "pmu.h"

void *xen_initial_gdt;

static int xen_cpu_up_prepare_pv(unsigned int cpu);
static int xen_cpu_dead_pv(unsigned int cpu);

struct tls_descs {
	struct desc_struct desc[3];
};

/*
 * Updating the 3 TLS descriptors in the GDT on every task switch is
 * surprisingly expensive so we avoid updating them if they haven't
 * changed.  Since Xen writes different descriptors than the one
 * passed in the update_descriptor hypercall we keep shadow copies to
 * compare against.
 */
static DEFINE_PER_CPU(struct tls_descs, shadow_tls_desc);

static void __init xen_banner(void)
{
	unsigned version = HYPERVISOR_xen_version(XENVER_version, NULL);
	struct xen_extraversion extra;
	HYPERVISOR_xen_version(XENVER_extraversion, &extra);

	pr_info("Booting paravirtualized kernel on %s\n", pv_info.name);
	printk(KERN_INFO "Xen version: %d.%d%s%s\n",
	       version >> 16, version & 0xffff, extra.extraversion,
	       xen_feature(XENFEAT_mmu_pt_update_preserve_ad) ? " (preserve-AD)" : "");
}
/* Check if running on Xen version (major, minor) or later */
bool
xen_running_on_version_or_later(unsigned int major, unsigned int minor)
{
	unsigned int version;

	if (!xen_domain())
		return false;

	version = HYPERVISOR_xen_version(XENVER_version, NULL);
	if ((((version >> 16) == major) && ((version & 0xffff) >= minor)) ||
		((version >> 16) > major))
		return true;
	return false;
}

static __read_mostly unsigned int cpuid_leaf5_ecx_val;
static __read_mostly unsigned int cpuid_leaf5_edx_val;

static void xen_cpuid(unsigned int *ax, unsigned int *bx,
		      unsigned int *cx, unsigned int *dx)
{
	unsigned maskebx = ~0;

	/*
	 * Mask out inconvenient features, to try and disable as many
	 * unsupported kernel subsystems as possible.
	 */
	switch (*ax) {
	case CPUID_MWAIT_LEAF:
		/* Synthesize the values.. */
		*ax = 0;
		*bx = 0;
		*cx = cpuid_leaf5_ecx_val;
		*dx = cpuid_leaf5_edx_val;
		return;

	case 0xb:
		/* Suppress extended topology stuff */
		maskebx = 0;
		break;
	}

	asm(XEN_EMULATE_PREFIX "cpuid"
		: "=a" (*ax),
		  "=b" (*bx),
		  "=c" (*cx),
		  "=d" (*dx)
		: "0" (*ax), "2" (*cx));

	*bx &= maskebx;
}
STACK_FRAME_NON_STANDARD(xen_cpuid); /* XEN_EMULATE_PREFIX */

static bool __init xen_check_mwait(void)
{
#ifdef CONFIG_ACPI
	struct xen_platform_op op = {
		.cmd			= XENPF_set_processor_pminfo,
		.u.set_pminfo.id	= -1,
		.u.set_pminfo.type	= XEN_PM_PDC,
	};
	uint32_t buf[3];
	unsigned int ax, bx, cx, dx;
	unsigned int mwait_mask;

	/* We need to determine whether it is OK to expose the MWAIT
	 * capability to the kernel to harvest deeper than C3 states from ACPI
	 * _CST using the processor_harvest_xen.c module. For this to work, we
	 * need to gather the MWAIT_LEAF values (which the cstate.c code
	 * checks against). The hypervisor won't expose the MWAIT flag because
	 * it would break backwards compatibility; so we will find out directly
	 * from the hardware and hypercall.
	 */
	if (!xen_initial_domain())
		return false;

	/*
	 * When running under platform earlier than Xen4.2, do not expose
	 * mwait, to avoid the risk of loading native acpi pad driver
	 */
	if (!xen_running_on_version_or_later(4, 2))
		return false;

	ax = 1;
	cx = 0;

	native_cpuid(&ax, &bx, &cx, &dx);

	mwait_mask = (1 << (X86_FEATURE_EST % 32)) |
		     (1 << (X86_FEATURE_MWAIT % 32));

	if ((cx & mwait_mask) != mwait_mask)
		return false;

	/* We need to emulate the MWAIT_LEAF and for that we need both
	 * ecx and edx. The hypercall provides only partial information.
	 */

	ax = CPUID_MWAIT_LEAF;
	bx = 0;
	cx = 0;
	dx = 0;

	native_cpuid(&ax, &bx, &cx, &dx);

	/* Ask the Hypervisor whether to clear ACPI_PDC_C_C2C3_FFH. If so,
	 * don't expose MWAIT_LEAF and let ACPI pick the IOPORT version of C3.
	 */
	buf[0] = ACPI_PDC_REVISION_ID;
	buf[1] = 1;
	buf[2] = (ACPI_PDC_C_CAPABILITY_SMP | ACPI_PDC_EST_CAPABILITY_SWSMP);

	set_xen_guest_handle(op.u.set_pminfo.pdc, buf);

	if ((HYPERVISOR_platform_op(&op) == 0) &&
	    (buf[2] & (ACPI_PDC_C_C1_FFH | ACPI_PDC_C_C2C3_FFH))) {
		cpuid_leaf5_ecx_val = cx;
		cpuid_leaf5_edx_val = dx;
	}
	return true;
#else
	return false;
#endif
}

static bool __init xen_check_xsave(void)
{
	unsigned int cx, xsave_mask;

	cx = cpuid_ecx(1);

	xsave_mask = (1 << (X86_FEATURE_XSAVE % 32)) |
		     (1 << (X86_FEATURE_OSXSAVE % 32));

	/* Xen will set CR4.OSXSAVE if supported and not disabled by force */
	return (cx & xsave_mask) == xsave_mask;
}

static void __init xen_init_capabilities(void)
{
	setup_force_cpu_cap(X86_FEATURE_XENPV);
	setup_clear_cpu_cap(X86_FEATURE_DCA);
	setup_clear_cpu_cap(X86_FEATURE_APERFMPERF);
	setup_clear_cpu_cap(X86_FEATURE_MTRR);
	setup_clear_cpu_cap(X86_FEATURE_ACC);
	setup_clear_cpu_cap(X86_FEATURE_X2APIC);

	if (!xen_initial_domain())
		setup_clear_cpu_cap(X86_FEATURE_ACPI);

	if (xen_check_mwait())
		setup_force_cpu_cap(X86_FEATURE_MWAIT);
	else
		setup_clear_cpu_cap(X86_FEATURE_MWAIT);

	if (!xen_check_xsave()) {
		setup_clear_cpu_cap(X86_FEATURE_XSAVE);
		setup_clear_cpu_cap(X86_FEATURE_OSXSAVE);
	}
}

static void xen_set_debugreg(int reg, unsigned long val)
{
	HYPERVISOR_set_debugreg(reg, val);
}

static unsigned long xen_get_debugreg(int reg)
{
	return HYPERVISOR_get_debugreg(reg);
}

static void xen_end_context_switch(struct task_struct *next)
{
	xen_mc_flush();
	paravirt_end_context_switch(next);
}

static unsigned long xen_store_tr(void)
{
	return 0;
}

/*
 * Set the page permissions for a particular virtual address.  If the
 * address is a vmalloc mapping (or other non-linear mapping), then
 * find the linear mapping of the page and also set its protections to
 * match.
 */
static void set_aliased_prot(void *v, pgprot_t prot)
{
	int level;
	pte_t *ptep;
	pte_t pte;
	unsigned long pfn;
	struct page *page;
	unsigned char dummy;

	ptep = lookup_address((unsigned long)v, &level);
	BUG_ON(ptep == NULL);

	pfn = pte_pfn(*ptep);
	page = pfn_to_page(pfn);

	pte = pfn_pte(pfn, prot);

	/*
	 * Careful: update_va_mapping() will fail if the virtual address
	 * we're poking isn't populated in the page tables.  We don't
	 * need to worry about the direct map (that's always in the page
	 * tables), but we need to be careful about vmap space.  In
	 * particular, the top level page table can lazily propagate
	 * entries between processes, so if we've switched mms since we
	 * vmapped the target in the first place, we might not have the
	 * top-level page table entry populated.
	 *
	 * We disable preemption because we want the same mm active when
	 * we probe the target and when we issue the hypercall.  We'll
	 * have the same nominal mm, but if we're a kernel thread, lazy
	 * mm dropping could change our pgd.
	 *
	 * Out of an abundance of caution, this uses __get_user() to fault
	 * in the target address just in case there's some obscure case
	 * in which the target address isn't readable.
	 */

	preempt_disable();

	probe_kernel_read(&dummy, v, 1);

	if (HYPERVISOR_update_va_mapping((unsigned long)v, pte, 0))
		BUG();

	if (!PageHighMem(page)) {
		void *av = __va(PFN_PHYS(pfn));

		if (av != v)
			if (HYPERVISOR_update_va_mapping((unsigned long)av, pte, 0))
				BUG();
	} else
		kmap_flush_unused();

	preempt_enable();
}

static void xen_alloc_ldt(struct desc_struct *ldt, unsigned entries)
{
	const unsigned entries_per_page = PAGE_SIZE / LDT_ENTRY_SIZE;
	int i;

	/*
	 * We need to mark the all aliases of the LDT pages RO.  We
	 * don't need to call vm_flush_aliases(), though, since that's
	 * only responsible for flushing aliases out the TLBs, not the
	 * page tables, and Xen will flush the TLB for us if needed.
	 *
	 * To avoid confusing future readers: none of this is necessary
	 * to load the LDT.  The hypervisor only checks this when the
	 * LDT is faulted in due to subsequent descriptor access.
	 */

	for (i = 0; i < entries; i += entries_per_page)
		set_aliased_prot(ldt + i, PAGE_KERNEL_RO);
}

static void xen_free_ldt(struct desc_struct *ldt, unsigned entries)
{
	const unsigned entries_per_page = PAGE_SIZE / LDT_ENTRY_SIZE;
	int i;

	for (i = 0; i < entries; i += entries_per_page)
		set_aliased_prot(ldt + i, PAGE_KERNEL);
}

static void xen_set_ldt(const void *addr, unsigned entries)
{
	struct mmuext_op *op;
	struct multicall_space mcs = xen_mc_entry(sizeof(*op));

	trace_xen_cpu_set_ldt(addr, entries);

	op = mcs.args;
	op->cmd = MMUEXT_SET_LDT;
	op->arg1.linear_addr = (unsigned long)addr;
	op->arg2.nr_ents = entries;

	MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);

	xen_mc_issue(PARAVIRT_LAZY_CPU);
}

static void xen_load_gdt(const struct desc_ptr *dtr)
{
	unsigned long va = dtr->address;
	unsigned int size = dtr->size + 1;
	unsigned pages = DIV_ROUND_UP(size, PAGE_SIZE);
	unsigned long frames[pages];
	int f;

	/*
	 * A GDT can be up to 64k in size, which corresponds to 8192
	 * 8-byte entries, or 16 4k pages..
	 */

	BUG_ON(size > 65536);
	BUG_ON(va & ~PAGE_MASK);

	for (f = 0; va < dtr->address + size; va += PAGE_SIZE, f++) {
		int level;
		pte_t *ptep;
		unsigned long pfn, mfn;
		void *virt;

		/*
		 * The GDT is per-cpu and is in the percpu data area.
		 * That can be virtually mapped, so we need to do a
		 * page-walk to get the underlying MFN for the
		 * hypercall.  The page can also be in the kernel's
		 * linear range, so we need to RO that mapping too.
		 */
		ptep = lookup_address(va, &level);
		BUG_ON(ptep == NULL);

		pfn = pte_pfn(*ptep);
		mfn = pfn_to_mfn(pfn);
		virt = __va(PFN_PHYS(pfn));

		frames[f] = mfn;

		make_lowmem_page_readonly((void *)va);
		make_lowmem_page_readonly(virt);
	}

	if (HYPERVISOR_set_gdt(frames, size / sizeof(struct desc_struct)))
		BUG();
}

/*
 * load_gdt for early boot, when the gdt is only mapped once
 */
static void __init xen_load_gdt_boot(const struct desc_ptr *dtr)
{
	unsigned long va = dtr->address;
	unsigned int size = dtr->size + 1;
	unsigned pages = DIV_ROUND_UP(size, PAGE_SIZE);
	unsigned long frames[pages];
	int f;

	/*
	 * A GDT can be up to 64k in size, which corresponds to 8192
	 * 8-byte entries, or 16 4k pages..
	 */

	BUG_ON(size > 65536);
	BUG_ON(va & ~PAGE_MASK);

	for (f = 0; va < dtr->address + size; va += PAGE_SIZE, f++) {
		pte_t pte;
		unsigned long pfn, mfn;

		pfn = virt_to_pfn(va);
		mfn = pfn_to_mfn(pfn);

		pte = pfn_pte(pfn, PAGE_KERNEL_RO);

		if (HYPERVISOR_update_va_mapping((unsigned long)va, pte, 0))
			BUG();

		frames[f] = mfn;
	}

	if (HYPERVISOR_set_gdt(frames, size / sizeof(struct desc_struct)))
		BUG();
}

static inline bool desc_equal(const struct desc_struct *d1,
			      const struct desc_struct *d2)
{
	return d1->a == d2->a && d1->b == d2->b;
}

static void load_TLS_descriptor(struct thread_struct *t,
				unsigned int cpu, unsigned int i)
{
	struct desc_struct *shadow = &per_cpu(shadow_tls_desc, cpu).desc[i];
	struct desc_struct *gdt;
	xmaddr_t maddr;
	struct multicall_space mc;

	if (desc_equal(shadow, &t->tls_array[i]))
		return;

	*shadow = t->tls_array[i];

	gdt = get_cpu_gdt_rw(cpu);
	maddr = arbitrary_virt_to_machine(&gdt[GDT_ENTRY_TLS_MIN+i]);
	mc = __xen_mc_entry(0);

	MULTI_update_descriptor(mc.mc, maddr.maddr, t->tls_array[i]);
}

static void xen_load_tls(struct thread_struct *t, unsigned int cpu)
{
	/*
	 * XXX sleazy hack: If we're being called in a lazy-cpu zone
	 * and lazy gs handling is enabled, it means we're in a
	 * context switch, and %gs has just been saved.  This means we
	 * can zero it out to prevent faults on exit from the
	 * hypervisor if the next process has no %gs.  Either way, it
	 * has been saved, and the new value will get loaded properly.
	 * This will go away as soon as Xen has been modified to not
	 * save/restore %gs for normal hypercalls.
	 *
	 * On x86_64, this hack is not used for %gs, because gs points
	 * to KERNEL_GS_BASE (and uses it for PDA references), so we
	 * must not zero %gs on x86_64
	 *
	 * For x86_64, we need to zero %fs, otherwise we may get an
	 * exception between the new %fs descriptor being loaded and
	 * %fs being effectively cleared at __switch_to().
	 */
	if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_CPU) {
#ifdef CONFIG_X86_32
		lazy_load_gs(0);
#else
		loadsegment(fs, 0);
#endif
	}

	xen_mc_batch();

	load_TLS_descriptor(t, cpu, 0);
	load_TLS_descriptor(t, cpu, 1);
	load_TLS_descriptor(t, cpu, 2);

	xen_mc_issue(PARAVIRT_LAZY_CPU);
}

#ifdef CONFIG_X86_64
static void xen_load_gs_index(unsigned int idx)
{
	if (HYPERVISOR_set_segment_base(SEGBASE_GS_USER_SEL, idx))
		BUG();
}
#endif

static void xen_write_ldt_entry(struct desc_struct *dt, int entrynum,
				const void *ptr)
{
	xmaddr_t mach_lp = arbitrary_virt_to_machine(&dt[entrynum]);
	u64 entry = *(u64 *)ptr;

	trace_xen_cpu_write_ldt_entry(dt, entrynum, entry);

	preempt_disable();

	xen_mc_flush();
	if (HYPERVISOR_update_descriptor(mach_lp.maddr, entry))
		BUG();

	preempt_enable();
}

static int cvt_gate_to_trap(int vector, const gate_desc *val,
			    struct trap_info *info)
{
	unsigned long addr;

	if (val->type != GATE_TRAP && val->type != GATE_INTERRUPT)
		return 0;

	info->vector = vector;

	addr = gate_offset(*val);
#ifdef CONFIG_X86_64
	/*
	 * Look for known traps using IST, and substitute them
	 * appropriately.  The debugger ones are the only ones we care
	 * about.  Xen will handle faults like double_fault,
	 * so we should never see them.  Warn if
	 * there's an unexpected IST-using fault handler.
	 */
	if (addr == (unsigned long)debug)
		addr = (unsigned long)xen_debug;
	else if (addr == (unsigned long)int3)
		addr = (unsigned long)xen_int3;
	else if (addr == (unsigned long)stack_segment)
		addr = (unsigned long)xen_stack_segment;
	else if (addr == (unsigned long)double_fault) {
		/* Don't need to handle these */
		return 0;
#ifdef CONFIG_X86_MCE
	} else if (addr == (unsigned long)machine_check) {
		/*
		 * when xen hypervisor inject vMCE to guest,
		 * use native mce handler to handle it
		 */
		;
#endif
	} else if (addr == (unsigned long)nmi)
		/*
		 * Use the native version as well.
		 */
		;
	else {
		/* Some other trap using IST? */
		if (WARN_ON(val->ist != 0))
			return 0;
	}
#endif	/* CONFIG_X86_64 */
	info->address = addr;

	info->cs = gate_segment(*val);
	info->flags = val->dpl;
	/* interrupt gates clear IF */
	if (val->type == GATE_INTERRUPT)
		info->flags |= 1 << 2;

	return 1;
}

/* Locations of each CPU's IDT */
static DEFINE_PER_CPU(struct desc_ptr, idt_desc);

/* Set an IDT entry.  If the entry is part of the current IDT, then
   also update Xen. */
static void xen_write_idt_entry(gate_desc *dt, int entrynum, const gate_desc *g)
{
	unsigned long p = (unsigned long)&dt[entrynum];
	unsigned long start, end;

	trace_xen_cpu_write_idt_entry(dt, entrynum, g);

	preempt_disable();

	start = __this_cpu_read(idt_desc.address);
	end = start + __this_cpu_read(idt_desc.size) + 1;

	xen_mc_flush();

	native_write_idt_entry(dt, entrynum, g);

	if (p >= start && (p + 8) <= end) {
		struct trap_info info[2];

		info[1].address = 0;

		if (cvt_gate_to_trap(entrynum, g, &info[0]))
			if (HYPERVISOR_set_trap_table(info))
				BUG();
	}

	preempt_enable();
}

static void xen_convert_trap_info(const struct desc_ptr *desc,
				  struct trap_info *traps)
{
	unsigned in, out, count;

	count = (desc->size+1) / sizeof(gate_desc);
	BUG_ON(count > 256);

	for (in = out = 0; in < count; in++) {
		gate_desc *entry = (gate_desc *)(desc->address) + in;

		if (cvt_gate_to_trap(in, entry, &traps[out]))
			out++;
	}
	traps[out].address = 0;
}

void xen_copy_trap_info(struct trap_info *traps)
{
	const struct desc_ptr *desc = this_cpu_ptr(&idt_desc);

	xen_convert_trap_info(desc, traps);
}

/* Load a new IDT into Xen.  In principle this can be per-CPU, so we
   hold a spinlock to protect the static traps[] array (static because
   it avoids allocation, and saves stack space). */
static void xen_load_idt(const struct desc_ptr *desc)
{
	static DEFINE_SPINLOCK(lock);
	static struct trap_info traps[257];

	trace_xen_cpu_load_idt(desc);

	spin_lock(&lock);

	memcpy(this_cpu_ptr(&idt_desc), desc, sizeof(idt_desc));

	xen_convert_trap_info(desc, traps);

	xen_mc_flush();
	if (HYPERVISOR_set_trap_table(traps))
		BUG();

	spin_unlock(&lock);
}

/* Write a GDT descriptor entry.  Ignore LDT descriptors, since
   they're handled differently. */
static void xen_write_gdt_entry(struct desc_struct *dt, int entry,
				const void *desc, int type)
{
	trace_xen_cpu_write_gdt_entry(dt, entry, desc, type);

	preempt_disable();

	switch (type) {
	case DESC_LDT:
	case DESC_TSS:
		/* ignore */
		break;

	default: {
		xmaddr_t maddr = arbitrary_virt_to_machine(&dt[entry]);

		xen_mc_flush();
		if (HYPERVISOR_update_descriptor(maddr.maddr, *(u64 *)desc))
			BUG();
	}

	}

	preempt_enable();
}

/*
 * Version of write_gdt_entry for use at early boot-time needed to
 * update an entry as simply as possible.
 */
static void __init xen_write_gdt_entry_boot(struct desc_struct *dt, int entry,
					    const void *desc, int type)
{
	trace_xen_cpu_write_gdt_entry(dt, entry, desc, type);

	switch (type) {
	case DESC_LDT:
	case DESC_TSS:
		/* ignore */
		break;

	default: {
		xmaddr_t maddr = virt_to_machine(&dt[entry]);

		if (HYPERVISOR_update_descriptor(maddr.maddr, *(u64 *)desc))
			dt[entry] = *(struct desc_struct *)desc;
	}

	}
}

static void xen_load_sp0(struct tss_struct *tss,
			 struct thread_struct *thread)
{
	struct multicall_space mcs;

	mcs = xen_mc_entry(0);
	MULTI_stack_switch(mcs.mc, __KERNEL_DS, thread->sp0);
	xen_mc_issue(PARAVIRT_LAZY_CPU);
	tss->x86_tss.sp0 = thread->sp0;
}

void xen_set_iopl_mask(unsigned mask)
{
	struct physdev_set_iopl set_iopl;

	/* Force the change at ring 0. */
	set_iopl.iopl = (mask == 0) ? 1 : (mask >> 12) & 3;
	HYPERVISOR_physdev_op(PHYSDEVOP_set_iopl, &set_iopl);
}

static void xen_io_delay(void)
{
}

static DEFINE_PER_CPU(unsigned long, xen_cr0_value);

static unsigned long xen_read_cr0(void)
{
	unsigned long cr0 = this_cpu_read(xen_cr0_value);

	if (unlikely(cr0 == 0)) {
		cr0 = native_read_cr0();
		this_cpu_write(xen_cr0_value, cr0);
	}

	return cr0;
}

static void xen_write_cr0(unsigned long cr0)
{
	struct multicall_space mcs;

	this_cpu_write(xen_cr0_value, cr0);

	/* Only pay attention to cr0.TS; everything else is
	   ignored. */
	mcs = xen_mc_entry(0);

	MULTI_fpu_taskswitch(mcs.mc, (cr0 & X86_CR0_TS) != 0);

	xen_mc_issue(PARAVIRT_LAZY_CPU);
}

static void xen_write_cr4(unsigned long cr4)
{
	cr4 &= ~(X86_CR4_PGE | X86_CR4_PSE | X86_CR4_PCE);

	native_write_cr4(cr4);
}
#ifdef CONFIG_X86_64
static inline unsigned long xen_read_cr8(void)
{
	return 0;
}
static inline void xen_write_cr8(unsigned long val)
{
	BUG_ON(val);
}
#endif

static u64 xen_read_msr_safe(unsigned int msr, int *err)
{
	u64 val;

	if (pmu_msr_read(msr, &val, err))
		return val;

	val = native_read_msr_safe(msr, err);
	switch (msr) {
	case MSR_IA32_APICBASE:
#ifdef CONFIG_X86_X2APIC
		if (!(cpuid_ecx(1) & (1 << (X86_FEATURE_X2APIC & 31))))
#endif
			val &= ~X2APIC_ENABLE;
		break;
	}
	return val;
}

static int xen_write_msr_safe(unsigned int msr, unsigned low, unsigned high)
{
	int ret;

	ret = 0;

	switch (msr) {
#ifdef CONFIG_X86_64
		unsigned which;
		u64 base;

	case MSR_FS_BASE:		which = SEGBASE_FS; goto set;
	case MSR_KERNEL_GS_BASE:	which = SEGBASE_GS_USER; goto set;
	case MSR_GS_BASE:		which = SEGBASE_GS_KERNEL; goto set;

	set:
		base = ((u64)high << 32) | low;
		if (HYPERVISOR_set_segment_base(which, base) != 0)
			ret = -EIO;
		break;
#endif

	case MSR_STAR:
	case MSR_CSTAR:
	case MSR_LSTAR:
	case MSR_SYSCALL_MASK:
	case MSR_IA32_SYSENTER_CS:
	case MSR_IA32_SYSENTER_ESP:
	case MSR_IA32_SYSENTER_EIP:
		/* Fast syscall setup is all done in hypercalls, so
		   these are all ignored.  Stub them out here to stop
		   Xen console noise. */
		break;

	default:
		if (!pmu_msr_write(msr, low, high, &ret))
			ret = native_write_msr_safe(msr, low, high);
	}

	return ret;
}

static u64 xen_read_msr(unsigned int msr)
{
	/*
	 * This will silently swallow a #GP from RDMSR.  It may be worth
	 * changing that.
	 */
	int err;

	return xen_read_msr_safe(msr, &err);
}

static void xen_write_msr(unsigned int msr, unsigned low, unsigned high)
{
	/*
	 * This will silently swallow a #GP from WRMSR.  It may be worth
	 * changing that.
	 */
	xen_write_msr_safe(msr, low, high);
}

void xen_setup_shared_info(void)
{
	set_fixmap(FIX_PARAVIRT_BOOTMAP, xen_start_info->shared_info);

	HYPERVISOR_shared_info =
		(struct shared_info *)fix_to_virt(FIX_PARAVIRT_BOOTMAP);

	xen_setup_mfn_list_list();

	if (system_state == SYSTEM_BOOTING) {
#ifndef CONFIG_SMP
		/*
		 * In UP this is as good a place as any to set up shared info.
		 * Limit this to boot only, at restore vcpu setup is done via
		 * xen_vcpu_restore().
		 */
		xen_setup_vcpu_info_placement();
#endif
		/*
		 * Now that shared info is set up we can start using routines
		 * that point to pvclock area.
		 */
		xen_init_time_ops();
	}
}

/* This is called once we have the cpu_possible_mask */
void __ref xen_setup_vcpu_info_placement(void)
{
	int cpu;

	for_each_possible_cpu(cpu) {
		/* Set up direct vCPU id mapping for PV guests. */
		per_cpu(xen_vcpu_id, cpu) = cpu;

		/*
		 * xen_vcpu_setup(cpu) can fail  -- in which case it
		 * falls back to the shared_info version for cpus
		 * where xen_vcpu_nr(cpu) < MAX_VIRT_CPUS.
		 *
		 * xen_cpu_up_prepare_pv() handles the rest by failing
		 * them in hotplug.
		 */
		(void) xen_vcpu_setup(cpu);
	}

	/*
	 * xen_vcpu_setup managed to place the vcpu_info within the
	 * percpu area for all cpus, so make use of it.
	 */
	if (xen_have_vcpu_info_placement) {
		pv_irq_ops.save_fl = __PV_IS_CALLEE_SAVE(xen_save_fl_direct);
		pv_irq_ops.restore_fl = __PV_IS_CALLEE_SAVE(xen_restore_fl_direct);
		pv_irq_ops.irq_disable = __PV_IS_CALLEE_SAVE(xen_irq_disable_direct);
		pv_irq_ops.irq_enable = __PV_IS_CALLEE_SAVE(xen_irq_enable_direct);
		pv_mmu_ops.read_cr2 = xen_read_cr2_direct;
	}
}

static const struct pv_info xen_info __initconst = {
	.shared_kernel_pmd = 0,

#ifdef CONFIG_X86_64
	.extra_user_64bit_cs = FLAT_USER_CS64,
#endif
	.name = "Xen",
};

static const struct pv_cpu_ops xen_cpu_ops __initconst = {
	.cpuid = xen_cpuid,

	.set_debugreg = xen_set_debugreg,
	.get_debugreg = xen_get_debugreg,

	.read_cr0 = xen_read_cr0,
	.write_cr0 = xen_write_cr0,