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Bochs/bochs/plex86/kernel/nexus.S
Kevin Lawton 0768d01522 Added plex86 directory to bochs. This directory contains the 
new experimental stripped-down version of plex86, which is now
  a user-code-only VM.  I ripped out all the fancy stuff in plex86,
  such that under that right conditions, user-code (protection level 3)
  can run at near native speeds inside the plex86 VM.
The general idea is that bochs emulates all the initial real-mode code,
  and guest kernel code (protection level 0).  When it senses the
  right conditions (like the context switches to user-code), a shim
  is called to execute the guest inside the plex86 VM.  All guest-generated
  faults/exceptions are then forwarded back to bochs to be handled in
  the emulator.
Actually, I'm not yet adding the mods to the bochs code (other than
  the shim code which is in a separate file), until I hear that we're
  back in a more development mode with bochs after the 2.0 release.
The plex86 subdirectory is really a separate project.  It's just more
  convenient to co-develop it with bochs for now.  Both projects are
  currently LGPL, but each should be taken to be a separate project,
  and have their own license file.  Plex86 (it's only a kernel driver
  now) could ultimately be used with other projects, as it's modular.
  I talked with Bryce, and we both agreed it's OK to keep plex86 as
  a subdir in bochs for now.
2003-01-01 17:32:06 +00:00

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/*
* plex86: run multiple x86 operating systems concurrently
* Copyright (C) 1999-2001 Kevin P. Lawton
*
* nexus.S: code to transition between host and monitor/guest
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
.text
/* This module consists of relocatable code and data necessary to
* effect transitions between the host <--> guest. This information
* is purposely stored in this single page, so that we have access
* to it during our transitions between the monitor interrupt handler,
* and our host.
*
* I coded the relevant parts to use completely relocatable
* accesses to the following fields. This is necessary, so that
* we can float this code page anywhere in the monitor's linear
* address space.
*/
/* ===============================================================
* NOTE: If you modify ANY of the following fields, you must also
* update the corresponding entries in the C typedef 'nexus_t'.
* That construct is used from C land to access values in this
* relocatable page.
*/
.globl __nexus_start
__nexus_start:
__vm: ;.skip 4, 0
__host_gdt_info: ;.skip 6, 0
__host_idt_info: ;.skip 6, 0
__host_jmp_info: ;.skip 6, 0
__host_stack_info: ;.skip 6, 0
__host_ldt_sel: ;.skip 2, 0
__host_tss_sel: ;.skip 2, 0
__host_cr0: ;.skip 4, 0
__host_cr2: ;.skip 4, 0
__host_cr3: ;.skip 4, 0
__host_cr4: ;.skip 4, 0
__mon_gdt_info: ;.skip 6, 0
__mon_idt_info: ;.skip 6, 0
__mon_jmp_info: ;.skip 6, 0
__mon_stack_info: ;.skip 6, 0
__mon_ldt_sel: ;.skip 2, 0
__mon_tss_sel: ;.skip 2, 0
__mon_base: ;.skip 4, 0
__mon_cr0: ;.skip 4, 0
__mon_cr3: ;.skip 4, 0
__mon_cr4: ;.skip 4, 0
__mon_eflags: ;.skip 4, 0
__transition_pde: ;.skip 4, 0
__transition_pde_p_host: ;.skip 4, 0
__transition_pde_p_mon: ;.skip 4, 0
__transition_laddr: ;.skip 4, 0
/* ===============================================================
* End NOTE.
*/
#define OFFSET_OF(field) [field - __nexus_start]
/* These are the offsets of the structures above, from the */
/* beginning of this section. */
#define HOST_GDT_INFO OFFSET_OF(__host_gdt_info)
#define HOST_IDT_INFO OFFSET_OF(__host_idt_info)
#define HOST_JMP_INFO OFFSET_OF(__host_jmp_info)
#define HOST_STACK_INFO OFFSET_OF(__host_stack_info)
#define HOST_LDT_SEL OFFSET_OF(__host_ldt_sel)
#define HOST_TSS_SEL OFFSET_OF(__host_tss_sel)
#define HOST_CR0 OFFSET_OF(__host_cr0)
#define HOST_CR2 OFFSET_OF(__host_cr2)
#define HOST_CR3 OFFSET_OF(__host_cr3)
#define HOST_CR4 OFFSET_OF(__host_cr4)
#define MON_GDT_INFO OFFSET_OF(__mon_gdt_info)
#define MON_IDT_INFO OFFSET_OF(__mon_idt_info)
#define MON_JMP_INFO OFFSET_OF(__mon_jmp_info)
#define MON_STACK_INFO OFFSET_OF(__mon_stack_info)
#define MON_LDT_SEL OFFSET_OF(__mon_ldt_sel)
#define MON_TSS_SEL OFFSET_OF(__mon_tss_sel)
#define MON_CR0 OFFSET_OF(__mon_cr0)
#define MON_CR3 OFFSET_OF(__mon_cr3)
#define MON_CR4 OFFSET_OF(__mon_cr4)
#define MON_BASE OFFSET_OF(__mon_base)
#define TRANSITION_PDE OFFSET_OF(__transition_pde)
#define TRANSITION_PDE_P_HOST OFFSET_OF(__transition_pde_p_host)
#define TRANSITION_PDE_P_MON OFFSET_OF(__transition_pde_p_mon)
#define TRANSITION_LADDR OFFSET_OF(__transition_laddr)
/* To make this code page and data accesses to the fields above */
/* relocatable, I use the following conventions. I load EBX with */
/* a pointer to the beginning of this page, to be used with an */
/* access through the CS: segment. We can easily get the */
/* current EIP with a call/pop EBX, so the combination of CS:EBX, */
/* accesses this page no matter where it is located. */
/* ================================================================== */
.globl __host2mon /* Start function __host2mon() */
__host2mon:
/* Save host context first, so it can be restored later */
pushfl /* Save host flags */
pushal /* Save host general regs */
pushl %es /* Save host segments */
pushl %ds
pushl %fs
pushl %gs
/* Put EIP of beginning of this section in EBX to be used to */
/* access data. */
call null_call
null_call:
popl %ebx
subl $(OFFSET_OF(null_call)), %ebx
/* Create identity mapping of this page into the monitor context */
movl (TRANSITION_PDE_P_HOST)(%ebx), %eax
movl (TRANSITION_PDE)(%ebx), %ebp
xchgl %ebp, (%eax) /* old PDE saved in %ebp to be restored below */
/* Save host GDT, LDT, IDT, and TSS */
sgdt (HOST_GDT_INFO)(%ebx)
sidt (HOST_IDT_INFO)(%ebx)
sldt (HOST_LDT_SEL)(%ebx)
str (HOST_TSS_SEL)(%ebx)
movl %esp, (HOST_STACK_INFO)(%ebx) /* Save host SS:ESP */
movw %ss, (4+HOST_STACK_INFO)(%ebx) /* for later restore */
leal (OFFSET_OF(__host_cs))(%ebx), %eax /* Save the CS:EIP for monitor to */
movl %eax, (HOST_JMP_INFO)(%ebx) /* jump to when reloading host CS. */
movw %cs, (4+HOST_JMP_INFO)(%ebx) /* See __guest2host below. */
/* Save host CRx values */
movl %cr0, %eax
movl %cr2, %ecx
movl %cr4, %edx
movl %cr3, %esi
movl %eax, (HOST_CR0)(%ebx)
movl %ecx, (HOST_CR2)(%ebx)
movl %edx, (HOST_CR4)(%ebx)
movl %esi, (HOST_CR3)(%ebx)
/* Compute monitor CRx values */
movl (MON_CR0)(%ebx), %eax
movl (MON_CR4)(%ebx), %edx
movl (MON_CR3)(%ebx), %esi
/* Before changing the PSE bit in CR4, we have to switch over */
/* to the new CR3 (this page identity mapped anyways). Otherwise */
/* the processor could flush the TLB, and reload the entry for */
/* this page, only to find it's marked with a 4Meg Page, but we */
/* have that support turned off, before we actually */
/* reloaded CR3! */
movl %esi, %cr3 /* Set monitor CR3 */
movl %eax, %cr0 /* Set monitor CR0 */
movl %edx, %cr4 /* Set monitor CR4 */
movl %esi, %cr3 /* Set monitor CR3 */
jmp null_jmp0
null_jmp0:
/* Switch to monitor GDT, LDT, and IDT */
lgdt (MON_GDT_INFO)(%ebx)
lidt (MON_IDT_INFO)(%ebx)
lldt (MON_LDT_SEL)(%ebx)
/* Switch to monitor stack and CS */
/* and jump to the monitor-side nexus page */
lss (MON_STACK_INFO)(%ebx), %esp
ljmp (MON_JMP_INFO)(%ebx)
.globl __mon_cs
__mon_cs:
/* Reset DS:EBX to point to the monitor-side nexus page */
movw %ss, %ax
movw %ax, %ds /* copy SS to DS */
movw %ax, %es /* copy SS to ES */
movl %esp, %ebx
andl $0xfffff000, %ebx
/* Clear busy bit of the monitor TSS and switch to it */
movzwl (MON_TSS_SEL)(%ebx), %eax
andl $0xfffffff8, %eax
addl (MON_GDT_INFO+2)(%ebx), %eax
subl (MON_BASE)(%ebx), %eax
andl $0xfffffdff, 4(%eax)
ltr (MON_TSS_SEL)(%ebx)
/* We no longer need the nexus page identity mapped. Fix the mapping */
/* back to the way it should be, in case guest code uses it. */
movl (TRANSITION_PDE_P_MON)(%ebx), %eax
movl %ebp, (%eax) /* %ebp still contains the original value */
movl (TRANSITION_LADDR)(%ebx), %eax
invlpg (%eax) /* Tell TLB about the change */
/* +++ xxx fix this, need to convert pure laddr to offset */
movl %cr3, %eax /* +++ xxx */
movl %eax, %cr3 /* +++ xxx */
/* */
/* We can now restore the monitor context from it's stack. */
/* */
popl %gs
popl %fs
popal /* Restore mon general registers */
popfl /* Restore mon eflags */
ret /* Resume execution in monitor exception handler code. */
/* ================================================================== */
.globl __mon2host /* Start function __mon2host() */
__mon2host:
pushfl /* Save mon flags */
pushal /* Save mon general registers */
pushl %fs
pushl %gs
/* Set EBX to point to this nexus page */
movl %esp, %ebx
andl $0xfffff000, %ebx
movl %esp, (MON_STACK_INFO)(%ebx) /* Save mon ESP */
/* Identity map this code page to host address space. */
movl (TRANSITION_PDE_P_MON)(%ebx), %eax
movl (TRANSITION_PDE)(%ebx), %ebp
xchgl %ebp, (%eax) /* old PDE saved in %ebp to be restored below */
movl (TRANSITION_LADDR)(%ebx), %eax
/* Switch EBX to point to the identity mapped copy of */
/* the nexus page, and jump to the copy of this code there. */
subl (MON_BASE)(%ebx), %eax
invlpg (%eax) /* Tell TLB about the change */
movl %eax, %ebx
leal (OFFSET_OF(__mon_nexus_jmp))(%ebx), %eax
jmp *%eax
__mon_nexus_jmp:
/* We are still in the monitor context, but are running at the */
/* same CS.base+EIP location in either host or monitor context, */
/* and this page is identity mapped between the 2 contexts. */
/* We can now switch to the host CR3, and be sure that execution */
/* will resume at the next instruction. */
/* NOTE: Don't try to access the stack after CR3 was reloaded */
/* but before we switched back to the host stack! */
/* Restore host CRx values */
movl (HOST_CR0)(%ebx), %eax
movl (HOST_CR2)(%ebx), %ecx
movl (HOST_CR4)(%ebx), %edx
movl (HOST_CR3)(%ebx), %esi
movl %eax, %cr0
movl %ecx, %cr2
movl %edx, %cr4
movl %esi, %cr3
jmp null_jmp1
null_jmp1:
/* Switch to host GDT, LDT, and IDT */
lgdt (HOST_GDT_INFO)(%ebx)
lidt (HOST_IDT_INFO)(%ebx)
lldt (HOST_LDT_SEL)(%ebx)
/* Restore host stack and CS */
lss (HOST_STACK_INFO)(%ebx), %esp
ljmp (HOST_JMP_INFO)(%ebx)
__host_cs:
/* Clear busy bit of the host TSS and switch to it */
/* Note that DS is still the monitor segment with base (MON_BASE). */
movzwl (HOST_TSS_SEL)(%ebx), %eax
andl $0xfffffff8, %eax
addl (HOST_GDT_INFO+2)(%ebx), %eax
subl (MON_BASE)(%ebx), %eax
andl $0xfffffdff, 4(%eax)
ltr (HOST_TSS_SEL)(%ebx)
/* We no longer need the nexus page identity mapped, so we clean */
/* up the monitor page directory in case the host looks at it. */
/* Note that SS is already the host segment. */
movl (TRANSITION_PDE_P_HOST)(%ebx), %eax
ss; movl %ebp, (%eax) /* %ebp still contains the original value */
/* Now we can restore the rest of */
/* the host context from the host stack. Look at __host2guest */
/* for the format of the values stored on the host stack. */
popl %gs
popl %fs
popl %ds
popl %es
popal
popfl
ret
.globl __nexus_end
__nexus_end:
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