1
linux/include/asm-i386/xen/hypercall.h
Jeremy Fitzhardinge 5ead97c84f xen: Core Xen implementation
This patch is a rollup of all the core pieces of the Xen
implementation, including:
 - booting and setup
 - pagetable setup
 - privileged instructions
 - segmentation
 - interrupt flags
 - upcalls
 - multicall batching

BOOTING AND SETUP

The vmlinux image is decorated with ELF notes which tell the Xen
domain builder what the kernel's requirements are; the domain builder
then constructs the address space accordingly and starts the kernel.

Xen has its own entrypoint for the kernel (contained in an ELF note).
The ELF notes are set up by xen-head.S, which is included into head.S.
In principle it could be linked separately, but it seems to provoke
lots of binutils bugs.

Because the domain builder starts the kernel in a fairly sane state
(32-bit protected mode, paging enabled, flat segments set up), there's
not a lot of setup needed before starting the kernel proper.  The main
steps are:
  1. Install the Xen paravirt_ops, which is simply a matter of a
     structure assignment.
  2. Set init_mm to use the Xen-supplied pagetables (analogous to the
     head.S generated pagetables in a native boot).
  3. Reserve address space for Xen, since it takes a chunk at the top
     of the address space for its own use.
  4. Call start_kernel()

PAGETABLE SETUP

Once we hit the main kernel boot sequence, it will end up calling back
via paravirt_ops to set up various pieces of Xen specific state.  One
of the critical things which requires a bit of extra care is the
construction of the initial init_mm pagetable.  Because Xen places
tight constraints on pagetables (an active pagetable must always be
valid, and must always be mapped read-only to the guest domain), we
need to be careful when constructing the new pagetable to keep these
constraints in mind.  It turns out that the easiest way to do this is
use the initial Xen-provided pagetable as a template, and then just
insert new mappings for memory where a mapping doesn't already exist.

This means that during pagetable setup, it uses a special version of
xen_set_pte which ignores any attempt to remap a read-only page as
read-write (since Xen will map its own initial pagetable as RO), but
lets other changes to the ptes happen, so that things like NX are set
properly.

PRIVILEGED INSTRUCTIONS AND SEGMENTATION

When the kernel runs under Xen, it runs in ring 1 rather than ring 0.
This means that it is more privileged than user-mode in ring 3, but it
still can't run privileged instructions directly.  Non-performance
critical instructions are dealt with by taking a privilege exception
and trapping into the hypervisor and emulating the instruction, but
more performance-critical instructions have their own specific
paravirt_ops.  In many cases we can avoid having to do any hypercalls
for these instructions, or the Xen implementation is quite different
from the normal native version.

The privileged instructions fall into the broad classes of:
  Segmentation: setting up the GDT and the GDT entries, LDT,
     TLS and so on.  Xen doesn't allow the GDT to be directly
     modified; all GDT updates are done via hypercalls where the new
     entries can be validated.  This is important because Xen uses
     segment limits to prevent the guest kernel from damaging the
     hypervisor itself.
  Traps and exceptions: Xen uses a special format for trap entrypoints,
     so when the kernel wants to set an IDT entry, it needs to be
     converted to the form Xen expects.  Xen sets int 0x80 up specially
     so that the trap goes straight from userspace into the guest kernel
     without going via the hypervisor.  sysenter isn't supported.
  Kernel stack: The esp0 entry is extracted from the tss and provided to
     Xen.
  TLB operations: the various TLB calls are mapped into corresponding
     Xen hypercalls.
  Control registers: all the control registers are privileged.  The most
     important is cr3, which points to the base of the current pagetable,
     and we handle it specially.

Another instruction we treat specially is CPUID, even though its not
privileged.  We want to control what CPU features are visible to the
rest of the kernel, and so CPUID ends up going into a paravirt_op.
Xen implements this mainly to disable the ACPI and APIC subsystems.

INTERRUPT FLAGS

Xen maintains its own separate flag for masking events, which is
contained within the per-cpu vcpu_info structure.  Because the guest
kernel runs in ring 1 and not 0, the IF flag in EFLAGS is completely
ignored (and must be, because even if a guest domain disables
interrupts for itself, it can't disable them overall).

(A note on terminology: "events" and interrupts are effectively
synonymous.  However, rather than using an "enable flag", Xen uses a
"mask flag", which blocks event delivery when it is non-zero.)

There are paravirt_ops for each of cli/sti/save_fl/restore_fl, which
are implemented to manage the Xen event mask state.  The only thing
worth noting is that when events are unmasked, we need to explicitly
see if there's a pending event and call into the hypervisor to make
sure it gets delivered.

UPCALLS

Xen needs a couple of upcall (or callback) functions to be implemented
by each guest.  One is the event upcalls, which is how events
(interrupts, effectively) are delivered to the guests.  The other is
the failsafe callback, which is used to report errors in either
reloading a segment register, or caused by iret.  These are
implemented in i386/kernel/entry.S so they can jump into the normal
iret_exc path when necessary.

MULTICALL BATCHING

Xen provides a multicall mechanism, which allows multiple hypercalls
to be issued at once in order to mitigate the cost of trapping into
the hypervisor.  This is particularly useful for context switches,
since the 4-5 hypercalls they would normally need (reload cr3, update
TLS, maybe update LDT) can be reduced to one.  This patch implements a
generic batching mechanism for hypercalls, which gets used in many
places in the Xen code.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Cc: Ian Pratt <ian.pratt@xensource.com>
Cc: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
Cc: Adrian Bunk <bunk@stusta.de>
2007-07-18 08:47:42 -07:00

414 lines
11 KiB
C

/******************************************************************************
* hypercall.h
*
* Linux-specific hypervisor handling.
*
* Copyright (c) 2002-2004, K A Fraser
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License version 2
* as published by the Free Software Foundation; or, when distributed
* separately from the Linux kernel or incorporated into other
* software packages, subject to the following license:
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this source file (the "Software"), to deal in the Software without
* restriction, including without limitation the rights to use, copy, modify,
* merge, publish, distribute, sublicense, and/or sell copies of the Software,
* and to permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
* IN THE SOFTWARE.
*/
#ifndef __HYPERCALL_H__
#define __HYPERCALL_H__
#include <linux/errno.h>
#include <linux/string.h>
#include <xen/interface/xen.h>
#include <xen/interface/sched.h>
#include <xen/interface/physdev.h>
extern struct { char _entry[32]; } hypercall_page[];
#define _hypercall0(type, name) \
({ \
long __res; \
asm volatile ( \
"call %[call]" \
: "=a" (__res) \
: [call] "m" (hypercall_page[__HYPERVISOR_##name]) \
: "memory" ); \
(type)__res; \
})
#define _hypercall1(type, name, a1) \
({ \
long __res, __ign1; \
asm volatile ( \
"call %[call]" \
: "=a" (__res), "=b" (__ign1) \
: "1" ((long)(a1)), \
[call] "m" (hypercall_page[__HYPERVISOR_##name]) \
: "memory" ); \
(type)__res; \
})
#define _hypercall2(type, name, a1, a2) \
({ \
long __res, __ign1, __ign2; \
asm volatile ( \
"call %[call]" \
: "=a" (__res), "=b" (__ign1), "=c" (__ign2) \
: "1" ((long)(a1)), "2" ((long)(a2)), \
[call] "m" (hypercall_page[__HYPERVISOR_##name]) \
: "memory" ); \
(type)__res; \
})
#define _hypercall3(type, name, a1, a2, a3) \
({ \
long __res, __ign1, __ign2, __ign3; \
asm volatile ( \
"call %[call]" \
: "=a" (__res), "=b" (__ign1), "=c" (__ign2), \
"=d" (__ign3) \
: "1" ((long)(a1)), "2" ((long)(a2)), \
"3" ((long)(a3)), \
[call] "m" (hypercall_page[__HYPERVISOR_##name]) \
: "memory" ); \
(type)__res; \
})
#define _hypercall4(type, name, a1, a2, a3, a4) \
({ \
long __res, __ign1, __ign2, __ign3, __ign4; \
asm volatile ( \
"call %[call]" \
: "=a" (__res), "=b" (__ign1), "=c" (__ign2), \
"=d" (__ign3), "=S" (__ign4) \
: "1" ((long)(a1)), "2" ((long)(a2)), \
"3" ((long)(a3)), "4" ((long)(a4)), \
[call] "m" (hypercall_page[__HYPERVISOR_##name]) \
: "memory" ); \
(type)__res; \
})
#define _hypercall5(type, name, a1, a2, a3, a4, a5) \
({ \
long __res, __ign1, __ign2, __ign3, __ign4, __ign5; \
asm volatile ( \
"call %[call]" \
: "=a" (__res), "=b" (__ign1), "=c" (__ign2), \
"=d" (__ign3), "=S" (__ign4), "=D" (__ign5) \
: "1" ((long)(a1)), "2" ((long)(a2)), \
"3" ((long)(a3)), "4" ((long)(a4)), \
"5" ((long)(a5)), \
[call] "m" (hypercall_page[__HYPERVISOR_##name]) \
: "memory" ); \
(type)__res; \
})
static inline int
HYPERVISOR_set_trap_table(struct trap_info *table)
{
return _hypercall1(int, set_trap_table, table);
}
static inline int
HYPERVISOR_mmu_update(struct mmu_update *req, int count,
int *success_count, domid_t domid)
{
return _hypercall4(int, mmu_update, req, count, success_count, domid);
}
static inline int
HYPERVISOR_mmuext_op(struct mmuext_op *op, int count,
int *success_count, domid_t domid)
{
return _hypercall4(int, mmuext_op, op, count, success_count, domid);
}
static inline int
HYPERVISOR_set_gdt(unsigned long *frame_list, int entries)
{
return _hypercall2(int, set_gdt, frame_list, entries);
}
static inline int
HYPERVISOR_stack_switch(unsigned long ss, unsigned long esp)
{
return _hypercall2(int, stack_switch, ss, esp);
}
static inline int
HYPERVISOR_set_callbacks(unsigned long event_selector,
unsigned long event_address,
unsigned long failsafe_selector,
unsigned long failsafe_address)
{
return _hypercall4(int, set_callbacks,
event_selector, event_address,
failsafe_selector, failsafe_address);
}
static inline int
HYPERVISOR_fpu_taskswitch(int set)
{
return _hypercall1(int, fpu_taskswitch, set);
}
static inline int
HYPERVISOR_sched_op(int cmd, unsigned long arg)
{
return _hypercall2(int, sched_op, cmd, arg);
}
static inline long
HYPERVISOR_set_timer_op(u64 timeout)
{
unsigned long timeout_hi = (unsigned long)(timeout>>32);
unsigned long timeout_lo = (unsigned long)timeout;
return _hypercall2(long, set_timer_op, timeout_lo, timeout_hi);
}
static inline int
HYPERVISOR_set_debugreg(int reg, unsigned long value)
{
return _hypercall2(int, set_debugreg, reg, value);
}
static inline unsigned long
HYPERVISOR_get_debugreg(int reg)
{
return _hypercall1(unsigned long, get_debugreg, reg);
}
static inline int
HYPERVISOR_update_descriptor(u64 ma, u64 desc)
{
return _hypercall4(int, update_descriptor, ma, ma>>32, desc, desc>>32);
}
static inline int
HYPERVISOR_memory_op(unsigned int cmd, void *arg)
{
return _hypercall2(int, memory_op, cmd, arg);
}
static inline int
HYPERVISOR_multicall(void *call_list, int nr_calls)
{
return _hypercall2(int, multicall, call_list, nr_calls);
}
static inline int
HYPERVISOR_update_va_mapping(unsigned long va, pte_t new_val,
unsigned long flags)
{
unsigned long pte_hi = 0;
#ifdef CONFIG_X86_PAE
pte_hi = new_val.pte_high;
#endif
return _hypercall4(int, update_va_mapping, va,
new_val.pte_low, pte_hi, flags);
}
static inline int
HYPERVISOR_event_channel_op(int cmd, void *arg)
{
int rc = _hypercall2(int, event_channel_op, cmd, arg);
if (unlikely(rc == -ENOSYS)) {
struct evtchn_op op;
op.cmd = cmd;
memcpy(&op.u, arg, sizeof(op.u));
rc = _hypercall1(int, event_channel_op_compat, &op);
memcpy(arg, &op.u, sizeof(op.u));
}
return rc;
}
static inline int
HYPERVISOR_xen_version(int cmd, void *arg)
{
return _hypercall2(int, xen_version, cmd, arg);
}
static inline int
HYPERVISOR_console_io(int cmd, int count, char *str)
{
return _hypercall3(int, console_io, cmd, count, str);
}
static inline int
HYPERVISOR_physdev_op(int cmd, void *arg)
{
int rc = _hypercall2(int, physdev_op, cmd, arg);
if (unlikely(rc == -ENOSYS)) {
struct physdev_op op;
op.cmd = cmd;
memcpy(&op.u, arg, sizeof(op.u));
rc = _hypercall1(int, physdev_op_compat, &op);
memcpy(arg, &op.u, sizeof(op.u));
}
return rc;
}
static inline int
HYPERVISOR_grant_table_op(unsigned int cmd, void *uop, unsigned int count)
{
return _hypercall3(int, grant_table_op, cmd, uop, count);
}
static inline int
HYPERVISOR_update_va_mapping_otherdomain(unsigned long va, pte_t new_val,
unsigned long flags, domid_t domid)
{
unsigned long pte_hi = 0;
#ifdef CONFIG_X86_PAE
pte_hi = new_val.pte_high;
#endif
return _hypercall5(int, update_va_mapping_otherdomain, va,
new_val.pte_low, pte_hi, flags, domid);
}
static inline int
HYPERVISOR_vm_assist(unsigned int cmd, unsigned int type)
{
return _hypercall2(int, vm_assist, cmd, type);
}
static inline int
HYPERVISOR_vcpu_op(int cmd, int vcpuid, void *extra_args)
{
return _hypercall3(int, vcpu_op, cmd, vcpuid, extra_args);
}
static inline int
HYPERVISOR_suspend(unsigned long srec)
{
return _hypercall3(int, sched_op, SCHEDOP_shutdown,
SHUTDOWN_suspend, srec);
}
static inline int
HYPERVISOR_nmi_op(unsigned long op, unsigned long arg)
{
return _hypercall2(int, nmi_op, op, arg);
}
static inline void
MULTI_update_va_mapping(struct multicall_entry *mcl, unsigned long va,
pte_t new_val, unsigned long flags)
{
mcl->op = __HYPERVISOR_update_va_mapping;
mcl->args[0] = va;
#ifdef CONFIG_X86_PAE
mcl->args[1] = new_val.pte_low;
mcl->args[2] = new_val.pte_high;
#else
mcl->args[1] = new_val.pte_low;
mcl->args[2] = 0;
#endif
mcl->args[3] = flags;
}
static inline void
MULTI_grant_table_op(struct multicall_entry *mcl, unsigned int cmd,
void *uop, unsigned int count)
{
mcl->op = __HYPERVISOR_grant_table_op;
mcl->args[0] = cmd;
mcl->args[1] = (unsigned long)uop;
mcl->args[2] = count;
}
static inline void
MULTI_update_va_mapping_otherdomain(struct multicall_entry *mcl, unsigned long va,
pte_t new_val, unsigned long flags,
domid_t domid)
{
mcl->op = __HYPERVISOR_update_va_mapping_otherdomain;
mcl->args[0] = va;
#ifdef CONFIG_X86_PAE
mcl->args[1] = new_val.pte_low;
mcl->args[2] = new_val.pte_high;
#else
mcl->args[1] = new_val.pte_low;
mcl->args[2] = 0;
#endif
mcl->args[3] = flags;
mcl->args[4] = domid;
}
static inline void
MULTI_update_descriptor(struct multicall_entry *mcl, u64 maddr,
struct desc_struct desc)
{
mcl->op = __HYPERVISOR_update_descriptor;
mcl->args[0] = maddr;
mcl->args[1] = maddr >> 32;
mcl->args[2] = desc.a;
mcl->args[3] = desc.b;
}
static inline void
MULTI_memory_op(struct multicall_entry *mcl, unsigned int cmd, void *arg)
{
mcl->op = __HYPERVISOR_memory_op;
mcl->args[0] = cmd;
mcl->args[1] = (unsigned long)arg;
}
static inline void
MULTI_mmu_update(struct multicall_entry *mcl, struct mmu_update *req,
int count, int *success_count, domid_t domid)
{
mcl->op = __HYPERVISOR_mmu_update;
mcl->args[0] = (unsigned long)req;
mcl->args[1] = count;
mcl->args[2] = (unsigned long)success_count;
mcl->args[3] = domid;
}
static inline void
MULTI_mmuext_op(struct multicall_entry *mcl, struct mmuext_op *op, int count,
int *success_count, domid_t domid)
{
mcl->op = __HYPERVISOR_mmuext_op;
mcl->args[0] = (unsigned long)op;
mcl->args[1] = count;
mcl->args[2] = (unsigned long)success_count;
mcl->args[3] = domid;
}
static inline void
MULTI_set_gdt(struct multicall_entry *mcl, unsigned long *frames, int entries)
{
mcl->op = __HYPERVISOR_set_gdt;
mcl->args[0] = (unsigned long)frames;
mcl->args[1] = entries;
}
static inline void
MULTI_stack_switch(struct multicall_entry *mcl,
unsigned long ss, unsigned long esp)
{
mcl->op = __HYPERVISOR_stack_switch;
mcl->args[0] = ss;
mcl->args[1] = esp;
}
#endif /* __HYPERCALL_H__ */