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/*P:900 This is the Switcher: code which sits at 0xFFC00000 to do the low-level
* Guest<->Host switch. It is as simple as it can be made, but it's naturally
* very specific to x86.
*
* You have now completed Preparation. If this has whet your appetite; if you
* are feeling invigorated and refreshed then the next, more challenging stage
* can be found in "make Guest". :*/
#include <linux/linkage.h>
#include <asm/asm-offsets.h>
#include "lg.h"
.text
ENTRY(start_switcher_text)
/* %eax points to lguest pages for this CPU. %ebx contains cr3 value.
All normal registers can be clobbered! */
ENTRY(switch_to_guest)
/* Save host segments on host stack. */
pushl %es
pushl %ds
pushl %gs
pushl %fs
/* With CONFIG_FRAME_POINTER, gcc doesn't let us clobber this! */
pushl %ebp
/* Save host stack. */
movl %esp, LGUEST_PAGES_host_sp(%eax)
/* Switch to guest stack: if we get NMI we expect to be there. */
movl %eax, %edx
addl $LGUEST_PAGES_regs, %edx
movl %edx, %esp
/* Switch to guest's GDT, IDT. */
lgdt LGUEST_PAGES_guest_gdt_desc(%eax)
lidt LGUEST_PAGES_guest_idt_desc(%eax)
/* Switch to guest's TSS while GDT still writable. */
movl $(GDT_ENTRY_TSS*8), %edx
ltr %dx
/* Set host's TSS GDT entry to available (clear byte 5 bit 2). */
movl (LGUEST_PAGES_host_gdt_desc+2)(%eax), %edx
andb $0xFD, (GDT_ENTRY_TSS*8 + 5)(%edx)
/* Switch to guest page tables: lguest_pages->state now read-only. */
movl %ebx, %cr3
/* Restore guest regs */
popl %ebx
popl %ecx
popl %edx
popl %esi
popl %edi
popl %ebp
popl %gs
popl %eax
popl %fs
popl %ds
popl %es
/* Skip error code and trap number */
addl $8, %esp
iret
#define SWITCH_TO_HOST \
/* Save guest state */ \
pushl %es; \
pushl %ds; \
pushl %fs; \
pushl %eax; \
pushl %gs; \
pushl %ebp; \
pushl %edi; \
pushl %esi; \
pushl %edx; \
pushl %ecx; \
pushl %ebx; \
/* Load lguest ds segment for convenience. */ \
movl $(LGUEST_DS), %eax; \
movl %eax, %ds; \
/* Figure out where we are, based on stack (at top of regs). */ \
movl %esp, %eax; \
subl $LGUEST_PAGES_regs, %eax; \
/* Put trap number in %ebx before we switch cr3 and lose it. */ \
movl LGUEST_PAGES_regs_trapnum(%eax), %ebx; \
/* Switch to host page tables (host GDT, IDT and stack are in host \
mem, so need this first) */ \
movl LGUEST_PAGES_host_cr3(%eax), %edx; \
movl %edx, %cr3; \
/* Set guest's TSS to available (clear byte 5 bit 2). */ \
andb $0xFD, (LGUEST_PAGES_guest_gdt+GDT_ENTRY_TSS*8+5)(%eax); \
/* Switch to host's GDT & IDT. */ \
lgdt LGUEST_PAGES_host_gdt_desc(%eax); \
lidt LGUEST_PAGES_host_idt_desc(%eax); \
/* Switch to host's stack. */ \
movl LGUEST_PAGES_host_sp(%eax), %esp; \
/* Switch to host's TSS */ \
movl $(GDT_ENTRY_TSS*8), %edx; \
ltr %dx; \
popl %ebp; \
popl %fs; \
popl %gs; \
popl %ds; \
popl %es
/* Return to run_guest_once. */
return_to_host:
SWITCH_TO_HOST
iret
deliver_to_host:
SWITCH_TO_HOST
/* Decode IDT and jump to hosts' irq handler. When that does iret, it
* will return to run_guest_once. This is a feature. */
movl (LGUEST_PAGES_host_idt_desc+2)(%eax), %edx
leal (%edx,%ebx,8), %eax
movzwl (%eax),%edx
movl 4(%eax), %eax
xorw %ax, %ax
orl %eax, %edx
jmp *%edx
/* Real hardware interrupts are delivered straight to the host. Others
cause us to return to run_guest_once so it can decide what to do. Note
that some of these are overridden by the guest to deliver directly, and
never enter here (see load_guest_idt_entry). */
.macro IRQ_STUB N TARGET
.data; .long 1f; .text; 1:
/* Make an error number for most traps, which don't have one. */
.if (\N <> 8) && (\N < 10 || \N > 14) && (\N <> 17)
pushl $0
.endif
pushl $\N
jmp \TARGET
ALIGN
.endm
.macro IRQ_STUBS FIRST LAST TARGET
irq=\FIRST
.rept \LAST-\FIRST+1
IRQ_STUB irq \TARGET
irq=irq+1
.endr
.endm
/* We intercept every interrupt, because we may need to switch back to
* host. Unfortunately we can't tell them apart except by entry
* point, so we need 256 entry points.
*/
.data
.global default_idt_entries
default_idt_entries:
.text
IRQ_STUBS 0 1 return_to_host /* First two traps */
IRQ_STUB 2 handle_nmi /* NMI */
IRQ_STUBS 3 31 return_to_host /* Rest of traps */
IRQ_STUBS 32 127 deliver_to_host /* Real interrupts */
IRQ_STUB 128 return_to_host /* System call (overridden) */
IRQ_STUBS 129 255 deliver_to_host /* Other real interrupts */
/* We ignore NMI and return. */
handle_nmi:
addl $8, %esp
iret
ENTRY(end_switcher_text)
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