linux/include/asm-i386/segment.h
Rusty Russell 78be3706b2 [PATCH] i386: Allow a kernel not to be in ring 0
We allow for the fact that the guest kernel may not run in ring 0.  This
requires some abstraction in a few places when setting %cs or checking
privilege level (user vs kernel).

This is Chris' [RFC PATCH 15/33] move segment checks to subarch, except rather
than using #define USER_MODE_MASK which depends on a config option, we use
Zach's more flexible approach of assuming ring 3 == userspace.  I also used
"get_kernel_rpl()" over "get_kernel_cs()" because I think it reads better in
the code...

1) Remove the hardcoded 3 and introduce #define SEGMENT_RPL_MASK 3 2) Add a
get_kernel_rpl() macro, and don't assume it's zero.

And:

Clean up of patch for letting kernel run other than ring 0:

a. Add some comments about the SEGMENT_IS_*_CODE() macros.
b. Add a USER_RPL macro.  (Code was comparing a value to a mask
   in some places and to the magic number 3 in other places.)
c. Add macros for table indicator field and use them.
d. Change the entry.S tests for LDT stack segment to use the macros

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Zachary Amsden <zach@vmware.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Andi Kleen <ak@suse.de>
2006-09-26 10:52:39 +02:00

133 lines
3.8 KiB
C

#ifndef _ASM_SEGMENT_H
#define _ASM_SEGMENT_H
/*
* The layout of the per-CPU GDT under Linux:
*
* 0 - null
* 1 - reserved
* 2 - reserved
* 3 - reserved
*
* 4 - unused <==== new cacheline
* 5 - unused
*
* ------- start of TLS (Thread-Local Storage) segments:
*
* 6 - TLS segment #1 [ glibc's TLS segment ]
* 7 - TLS segment #2 [ Wine's %fs Win32 segment ]
* 8 - TLS segment #3
* 9 - reserved
* 10 - reserved
* 11 - reserved
*
* ------- start of kernel segments:
*
* 12 - kernel code segment <==== new cacheline
* 13 - kernel data segment
* 14 - default user CS
* 15 - default user DS
* 16 - TSS
* 17 - LDT
* 18 - PNPBIOS support (16->32 gate)
* 19 - PNPBIOS support
* 20 - PNPBIOS support
* 21 - PNPBIOS support
* 22 - PNPBIOS support
* 23 - APM BIOS support
* 24 - APM BIOS support
* 25 - APM BIOS support
*
* 26 - ESPFIX small SS
* 27 - unused
* 28 - unused
* 29 - unused
* 30 - unused
* 31 - TSS for double fault handler
*/
#define GDT_ENTRY_TLS_ENTRIES 3
#define GDT_ENTRY_TLS_MIN 6
#define GDT_ENTRY_TLS_MAX (GDT_ENTRY_TLS_MIN + GDT_ENTRY_TLS_ENTRIES - 1)
#define TLS_SIZE (GDT_ENTRY_TLS_ENTRIES * 8)
#define GDT_ENTRY_DEFAULT_USER_CS 14
#define __USER_CS (GDT_ENTRY_DEFAULT_USER_CS * 8 + 3)
#define GDT_ENTRY_DEFAULT_USER_DS 15
#define __USER_DS (GDT_ENTRY_DEFAULT_USER_DS * 8 + 3)
#define GDT_ENTRY_KERNEL_BASE 12
#define GDT_ENTRY_KERNEL_CS (GDT_ENTRY_KERNEL_BASE + 0)
#define __KERNEL_CS (GDT_ENTRY_KERNEL_CS * 8)
#define GDT_ENTRY_KERNEL_DS (GDT_ENTRY_KERNEL_BASE + 1)
#define __KERNEL_DS (GDT_ENTRY_KERNEL_DS * 8)
#define GDT_ENTRY_TSS (GDT_ENTRY_KERNEL_BASE + 4)
#define GDT_ENTRY_LDT (GDT_ENTRY_KERNEL_BASE + 5)
#define GDT_ENTRY_PNPBIOS_BASE (GDT_ENTRY_KERNEL_BASE + 6)
#define GDT_ENTRY_APMBIOS_BASE (GDT_ENTRY_KERNEL_BASE + 11)
#define GDT_ENTRY_ESPFIX_SS (GDT_ENTRY_KERNEL_BASE + 14)
#define __ESPFIX_SS (GDT_ENTRY_ESPFIX_SS * 8)
#define GDT_ENTRY_DOUBLEFAULT_TSS 31
/*
* The GDT has 32 entries
*/
#define GDT_ENTRIES 32
#define GDT_SIZE (GDT_ENTRIES * 8)
/* Matches __KERNEL_CS and __USER_CS (they must be 2 entries apart) */
#define SEGMENT_IS_FLAT_CODE(x) (((x) & 0xec) == GDT_ENTRY_KERNEL_CS * 8)
/* Matches PNP_CS32 and PNP_CS16 (they must be consecutive) */
#define SEGMENT_IS_PNP_CODE(x) (((x) & 0xf4) == GDT_ENTRY_PNPBIOS_BASE * 8)
/* Simple and small GDT entries for booting only */
#define GDT_ENTRY_BOOT_CS 2
#define __BOOT_CS (GDT_ENTRY_BOOT_CS * 8)
#define GDT_ENTRY_BOOT_DS (GDT_ENTRY_BOOT_CS + 1)
#define __BOOT_DS (GDT_ENTRY_BOOT_DS * 8)
/* The PnP BIOS entries in the GDT */
#define GDT_ENTRY_PNPBIOS_CS32 (GDT_ENTRY_PNPBIOS_BASE + 0)
#define GDT_ENTRY_PNPBIOS_CS16 (GDT_ENTRY_PNPBIOS_BASE + 1)
#define GDT_ENTRY_PNPBIOS_DS (GDT_ENTRY_PNPBIOS_BASE + 2)
#define GDT_ENTRY_PNPBIOS_TS1 (GDT_ENTRY_PNPBIOS_BASE + 3)
#define GDT_ENTRY_PNPBIOS_TS2 (GDT_ENTRY_PNPBIOS_BASE + 4)
/* The PnP BIOS selectors */
#define PNP_CS32 (GDT_ENTRY_PNPBIOS_CS32 * 8) /* segment for calling fn */
#define PNP_CS16 (GDT_ENTRY_PNPBIOS_CS16 * 8) /* code segment for BIOS */
#define PNP_DS (GDT_ENTRY_PNPBIOS_DS * 8) /* data segment for BIOS */
#define PNP_TS1 (GDT_ENTRY_PNPBIOS_TS1 * 8) /* transfer data segment */
#define PNP_TS2 (GDT_ENTRY_PNPBIOS_TS2 * 8) /* another data segment */
/*
* The interrupt descriptor table has room for 256 idt's,
* the global descriptor table is dependent on the number
* of tasks we can have..
*/
#define IDT_ENTRIES 256
/* Bottom two bits of selector give the ring privilege level */
#define SEGMENT_RPL_MASK 0x3
/* Bit 2 is table indicator (LDT/GDT) */
#define SEGMENT_TI_MASK 0x4
/* User mode is privilege level 3 */
#define USER_RPL 0x3
/* LDT segment has TI set, GDT has it cleared */
#define SEGMENT_LDT 0x4
#define SEGMENT_GDT 0x0
#define get_kernel_rpl() 0
#endif