x86: Introduce GDT_ENTRY_INIT()

PATCH In review Akinobu Mita 3 participants 5 messages Aug 8, 2009 – Aug 10, 2009

Subsystems (4)

x86 Char and misc drivers Pnp support Apm driver

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Akinobu Mita

author

2009-08-08 09:49 UTC #0 lore raw

PATCH 1/1 x86: Introduce GDT_ENTRY_INIT()

GDT_ENTRY_INIT is static initializer of desc_struct.

We already have similar macro GDT_ENTRY() but it's static initializer for u64 and it cannot be used for desc_struct.

[[email protected]: spotted convertion error for GDT_ENTRY_APMBIOS_BASE+2]

Cc "H. Peter Anvin" <[email protected]>

Signed-off-by Akinobu Mita <[email protected]>

---
 arch/x86/include/asm/desc_defs.h      |    6 +++++
 arch/x86/include/asm/lguest.h         |    5 ++-
 arch/x86/include/asm/stackprotector.h |    2 +-
 arch/x86/kernel/apm_32.c              |    2 +-
 arch/x86/kernel/cpu/common.c          |   40 ++++++++++++++++----------------
 drivers/pnp/pnpbios/bioscalls.c       |    5 +---
 6 files changed, 32 insertions(+), 28 deletions(-)

arch/x86/include/asm/desc_defs.h +6 -0

index a6adefa..9d66848 100644
@@ -34,6 +34,12 @@ struct desc_struct {
 	};
 } __attribute__((packed));
 
+#define GDT_ENTRY_INIT(flags, base, limit) { { { \
+		.a = ((limit) & 0xffff) | (((base) & 0xffff) << 16), \
+		.b = (((base) & 0xff0000) >> 16) | (((flags) & 0xf0ff) << 8) | \
+			((limit) & 0xf0000) | ((base) & 0xff000000), \
+	} } }
+
 enum {
 	GATE_INTERRUPT = 0xE,
 	GATE_TRAP = 0xF,

arch/x86/include/asm/lguest.h +3 -2

index 313389c..94cd698 100644
@@ -91,8 +91,9 @@ static inline void lguest_set_ts(void)
 }
 
 /* Full 4G segment descriptors, suitable for CS and DS. */
-#define FULL_EXEC_SEGMENT ((struct desc_struct){ { {0x0000ffff, 0x00cf9b00} } })
-#define FULL_SEGMENT ((struct desc_struct){ { {0x0000ffff, 0x00cf9300} } })
+#define FULL_EXEC_SEGMENT \
+	((struct desc_struct)GDT_ENTRY_INIT(0xc09b, 0, 0xfffff))
+#define FULL_SEGMENT ((struct desc_struct)GDT_ENTRY_INIT(0xc093, 0, 0xfffff))
 
 #endif /* __ASSEMBLY__ */

arch/x86/include/asm/stackprotector.h +1 -1

index cdc5e0b..44efdff 100644
@@ -48,7 +48,7 @@
  * head_32 for boot CPU and setup_per_cpu_areas() for others.
  */
 #define GDT_STACK_CANARY_INIT						\
-	[GDT_ENTRY_STACK_CANARY] = { { { 0x00000018, 0x00409000 } } },
+	[GDT_ENTRY_STACK_CANARY] = GDT_ENTRY_INIT(0x4090, 0, 0x18),
 
 /*
  * Initialize the stackprotector canary value.

arch/x86/kernel/apm_32.c +1 -1

index b5e841b..febb2da 100644
@@ -403,7 +403,7 @@ static DECLARE_WAIT_QUEUE_HEAD(apm_waitqueue);
 static DECLARE_WAIT_QUEUE_HEAD(apm_suspend_waitqueue);
 static struct apm_user *user_list;
 static DEFINE_SPINLOCK(user_list_lock);
-static struct desc_struct bad_bios_desc = { { { 0, 0x00409200 } } };
+static struct desc_struct bad_bios_desc = GDT_ENTRY_INIT(0x4092, 0, 0);
 
 static const char driver_version[] = "1.16ac";	/* no spaces */

arch/x86/kernel/cpu/common.c +20 ~~-20~~

index f1961c0..b5764a2 100644
@@ -71,45 +71,45 @@ DEFINE_PER_CPU_PAGE_ALIGNED(struct gdt_page, gdt_page) = { .gdt = {
 	 * TLS descriptors are currently at a different place compared to i386.
 	 * Hopefully nobody expects them at a fixed place (Wine?)
 	 */
-	[GDT_ENTRY_KERNEL32_CS]		= { { { 0x0000ffff, 0x00cf9b00 } } },
-	[GDT_ENTRY_KERNEL_CS]		= { { { 0x0000ffff, 0x00af9b00 } } },
-	[GDT_ENTRY_KERNEL_DS]		= { { { 0x0000ffff, 0x00cf9300 } } },
-	[GDT_ENTRY_DEFAULT_USER32_CS]	= { { { 0x0000ffff, 0x00cffb00 } } },
-	[GDT_ENTRY_DEFAULT_USER_DS]	= { { { 0x0000ffff, 0x00cff300 } } },
-	[GDT_ENTRY_DEFAULT_USER_CS]	= { { { 0x0000ffff, 0x00affb00 } } },
+	[GDT_ENTRY_KERNEL32_CS]		= GDT_ENTRY_INIT(0xc09b, 0, 0xfffff),
+	[GDT_ENTRY_KERNEL_CS]		= GDT_ENTRY_INIT(0xa09b, 0, 0xfffff),
+	[GDT_ENTRY_KERNEL_DS]		= GDT_ENTRY_INIT(0xc093, 0, 0xfffff),
+	[GDT_ENTRY_DEFAULT_USER32_CS]	= GDT_ENTRY_INIT(0xc0fb, 0, 0xfffff),
+	[GDT_ENTRY_DEFAULT_USER_DS]	= GDT_ENTRY_INIT(0xc0f3, 0, 0xfffff),
+	[GDT_ENTRY_DEFAULT_USER_CS]	= GDT_ENTRY_INIT(0xa0fb, 0, 0xfffff),
 #else
-	[GDT_ENTRY_KERNEL_CS]		= { { { 0x0000ffff, 0x00cf9a00 } } },
-	[GDT_ENTRY_KERNEL_DS]		= { { { 0x0000ffff, 0x00cf9200 } } },
-	[GDT_ENTRY_DEFAULT_USER_CS]	= { { { 0x0000ffff, 0x00cffa00 } } },
-	[GDT_ENTRY_DEFAULT_USER_DS]	= { { { 0x0000ffff, 0x00cff200 } } },
+	[GDT_ENTRY_KERNEL_CS]		= GDT_ENTRY_INIT(0xc09a, 0, 0xfffff),
+	[GDT_ENTRY_KERNEL_DS]		= GDT_ENTRY_INIT(0xc092, 0, 0xfffff),
+	[GDT_ENTRY_DEFAULT_USER_CS]	= GDT_ENTRY_INIT(0xc0fa, 0, 0xfffff),
+	[GDT_ENTRY_DEFAULT_USER_DS]	= GDT_ENTRY_INIT(0xc0f2, 0, 0xfffff),
 	/*
 	 * Segments used for calling PnP BIOS have byte granularity.
 	 * They code segments and data segments have fixed 64k limits,
 	 * the transfer segment sizes are set at run time.
 	 */
 	/* 32-bit code */
-	[GDT_ENTRY_PNPBIOS_CS32]	= { { { 0x0000ffff, 0x00409a00 } } },
+	[GDT_ENTRY_PNPBIOS_CS32]	= GDT_ENTRY_INIT(0x409a, 0, 0xffff),
 	/* 16-bit code */
-	[GDT_ENTRY_PNPBIOS_CS16]	= { { { 0x0000ffff, 0x00009a00 } } },
+	[GDT_ENTRY_PNPBIOS_CS16]	= GDT_ENTRY_INIT(0x009a, 0, 0xffff),
 	/* 16-bit data */
-	[GDT_ENTRY_PNPBIOS_DS]		= { { { 0x0000ffff, 0x00009200 } } },
+	[GDT_ENTRY_PNPBIOS_DS]		= GDT_ENTRY_INIT(0x0092, 0, 0xffff),
 	/* 16-bit data */
-	[GDT_ENTRY_PNPBIOS_TS1]		= { { { 0x00000000, 0x00009200 } } },
+	[GDT_ENTRY_PNPBIOS_TS1]		= GDT_ENTRY_INIT(0x0092, 0, 0),
 	/* 16-bit data */
-	[GDT_ENTRY_PNPBIOS_TS2]		= { { { 0x00000000, 0x00009200 } } },
+	[GDT_ENTRY_PNPBIOS_TS2]		= GDT_ENTRY_INIT(0x0092, 0, 0),
 	/*
 	 * The APM segments have byte granularity and their bases
 	 * are set at run time.  All have 64k limits.
 	 */
 	/* 32-bit code */
-	[GDT_ENTRY_APMBIOS_BASE]	= { { { 0x0000ffff, 0x00409a00 } } },
+	[GDT_ENTRY_APMBIOS_BASE]	= GDT_ENTRY_INIT(0x409a, 0, 0xffff),
 	/* 16-bit code */
-	[GDT_ENTRY_APMBIOS_BASE+1]	= { { { 0x0000ffff, 0x00009a00 } } },
+	[GDT_ENTRY_APMBIOS_BASE+1]	= GDT_ENTRY_INIT(0x009a, 0, 0xffff),
 	/* data */
-	[GDT_ENTRY_APMBIOS_BASE+2]	= { { { 0x0000ffff, 0x00409200 } } },
+	[GDT_ENTRY_APMBIOS_BASE+2]	= GDT_ENTRY_INIT(0x4092, 0, 0xffff),
 
-	[GDT_ENTRY_ESPFIX_SS]		= { { { 0x0000ffff, 0x00cf9200 } } },
-	[GDT_ENTRY_PERCPU]		= { { { 0x0000ffff, 0x00cf9200 } } },
+	[GDT_ENTRY_ESPFIX_SS]		= GDT_ENTRY_INIT(0xc092, 0, 0xfffff),
+	[GDT_ENTRY_PERCPU]		= GDT_ENTRY_INIT(0xc092, 0, 0xfffff),
 	GDT_STACK_CANARY_INIT
 #endif
 } };

drivers/char/vr41xx_giu.c deleted +0 -0

deleted file mode 100644
index e69de29..0000000

drivers/pnp/pnpbios/bioscalls.c +1 -4

index 45ad3e9..bd035e3 100644
@@ -60,7 +60,7 @@ do { \
 	set_desc_limit(&gdt[(selname) >> 3], (size) - 1); \
 } while(0)
 
-static struct desc_struct bad_bios_desc;
+static struct desc_struct bad_bios_desc = GDT_ENTRY_INIT(0x4092, 0, 0);
 
 /*
  * At some point we want to use this stack frame pointer to unwind

@@ -476,9 +476,6 @@ void pnpbios_calls_init(union pnp_bios_install_struct *header)
 	pnp_bios_callpoint.offset = header->fields.pm16offset;
 	pnp_bios_callpoint.segment = PNP_CS16;
 
-	bad_bios_desc.a = 0;
-	bad_bios_desc.b = 0x00409200;
-
 	set_desc_base(&bad_bios_desc, (unsigned long)__va(0x40UL << 4));
 	set_desc_limit(&bad_bios_desc, 4095 - (0x40 << 4));
 	for_each_possible_cpu(i) {

tip-bot for Ingo Molnar

2009-08-08 15:49 UTC #1 lore raw

[tip:x86/asm] x86: Introduce GDT_ENTRY_INIT(), fix APM

Commit-ID:  72c4d8530244264317a662de9a55cc47e6c8e9df
Gitweb:     http://git.kernel.org/tip/72c4d8530244264317a662de9a55cc47e6c8e9df
Author:     Ingo Molnar <[email protected]>
AuthorDate: Mon, 3 Aug 2009 08:47:07 +0200
Committer:  Ingo Molnar <[email protected]>
CommitDate: Sat, 8 Aug 2009 17:47:12 +0200

x86: Introduce GDT_ENTRY_INIT(), fix APM

This crash:

[    0.891983] calling  cache_sysfs_init+0x0/0x1ee @ 1
[    0.897251] initcall cache_sysfs_init+0x0/0x1ee returned 0 after 405 usecs
[    0.904019] calling  mce_init_device+0x0/0x242 @ 1
[    0.909124] initcall mce_init_device+0x0/0x242 returned 0 after 347 usecs
[    0.915815] calling  apm_init+0x0/0x38d @ 1
[    0.919967] apm: BIOS version 1.2 Flags 0x07 (Driver version 1.16ac)
[    0.926813] general protection fault: 0000 [#1]
[    0.927269] last sysfs file:
[    0.927269] Modules linked in:
[    0.927269]
[    0.927269] Pid: 271, comm: kapmd Not tainted (2.6.31-rc3-00100-gd520da1-dirty #311) System Product Name
[    0.927269] EIP: 00c0:[<000082b2>] EFLAGS: 00010002 CPU: 0
[    0.927269] EIP is at 0x82b2
[    0.927269] EAX: 0000530e EBX: 00000000 ECX: 00000102 EDX: 00000000
[    0.927269] ESI: 00000000 EDI: f6a4bf44 EBP: 67890000 ESP: f6a4beec
[    0.927269]  DS: 00c8 ES: 0000 FS: 0000 GS: 0000 SS: 0068
[    0.927269] Process kapmd (pid: 271, ti=f6a4a000 task=f7142280 task.ti=f6a4a000)
[    0.927269] Stack:
[    0.927269]  0000828d 02160000 00b88092 f6a4bf3c c102a63d 00000060 f6a4bf3c f6a4bf44
[    0.927269] <0> 0000007b 0000007b 00000000 00000000 00000000 00000000 560aae9e 00000000
[    0.927269] <0> 00000200 f705fd74 00000000 c102af70 f6a4bf60 c102a6ec 0000530e 00000000
[    0.927269] Call Trace:
[    0.927269]  [<c102a63d>] ? __apm_bios_call_simple+0x7d/0x110
[    0.927269]  [<c102af70>] ? apm+0x0/0x6a0
[    0.927269]  [<c102a6ec>] ? apm_bios_call_simple+0x1c/0x50
[    0.927269]  [<c102b3f5>] ? apm+0x485/0x6a0
[    0.927269]  [<c1038e7a>] ? finish_task_switch+0x2a/0xb0
[    0.927269]  [<c164a69e>] ? schedule+0x31e/0x480
[    0.927269]  [<c102af70>] ? apm+0x0/0x6a0
[    0.927269]  [<c102af70>] ? apm+0x0/0x6a0
[    0.927269]  [<c1052654>] ? kthread+0x74/0x80
[    0.927269]  [<c10525e0>] ? kthread+0x0/0x80
[    0.927269]  [<c101d627>] ? kernel_thread_helper+0x7/0x10
[    0.927269] Code:  Bad EIP value.
[    0.927269] EIP: [<000082b2>] 0x82b2 SS:ESP 0068:f6a4beec
[    0.927269] ---[ end trace a7919e7f17c0a725 ]---
[    0.927269] Kernel panic - not syncing: Fatal exception
[    0.927269] Pid: 271, comm: kapmd Tainted: G      D    2.6.31-rc3-00100-gd520da1-dirty #311

Is caused by an incorrect GDT_ENTRY_INIT() conversion in the apm code, as noticed by hpa.

Reported-by Ingo Molnar <[email protected]>

Noticed-by "H. Peter Anvin" <[email protected]>

Signed-off-by Akinobu Mita <[email protected]>

LKML-Reference: <[email protected]>

Signed-off-by Ingo Molnar <[email protected]>

---
 arch/x86/kernel/cpu/common.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

arch/x86/kernel/cpu/common.c +1 -1

index 8c9bc28..b5764a2 100644
@@ -106,7 +106,7 @@ DEFINE_PER_CPU_PAGE_ALIGNED(struct gdt_page, gdt_page) = { .gdt = {
 	/* 16-bit code */
 	[GDT_ENTRY_APMBIOS_BASE+1]	= GDT_ENTRY_INIT(0x009a, 0, 0xffff),
 	/* data */
-	[GDT_ENTRY_APMBIOS_BASE+2]	= GDT_ENTRY_INIT(0x409a, 0, 0xffff),
+	[GDT_ENTRY_APMBIOS_BASE+2]	= GDT_ENTRY_INIT(0x4092, 0, 0xffff),
 
 	[GDT_ENTRY_ESPFIX_SS]		= GDT_ENTRY_INIT(0xc092, 0, 0xfffff),
 	[GDT_ENTRY_PERCPU]		= GDT_ENTRY_INIT(0xc092, 0, 0xfffff),

H. Peter Anvin

reviewer

2009-08-08 21:07 UTC #2 lore raw

In reply to Akinobu Mita

Quoted 17 lines · Akinobu Mita

drivers/char/vr41xx_giu.c deleted +0 -0

deleted file mode 100644
index e69de29..0000000

drivers/pnp/pnpbios/bioscalls.c +1 -1

index 45ad3e9..bd035e3 100644
@@ -60,7 +60,7 @@ do { \
 	set_desc_limit(&gdt[(selname) >> 3], (size) - 1); \
 } while(0)
 
-static struct desc_struct bad_bios_desc;
+static struct desc_struct bad_bios_desc = GDT_ENTRY_INIT(0x4092, 0, 0);
 
 /*
  * At some point we want to use this stack frame pointer to unwind

drivers/pnp/pnpbios/bioscalls.c void pnpbios_calls_init(union pnp_bios_install_struct *header) · line 481

Quoted 9 lines

drivers/pnp/pnpbios/bioscalls.c +0 -3

@@ -476,9 +476,6 @@ void pnpbios_calls_init(union pnp_bios_install_struct *header)
 	pnp_bios_callpoint.offset = header->fields.pm16offset;
 	pnp_bios_callpoint.segment = PNP_CS16;
 
-	bad_bios_desc.a = 0;
-	bad_bios_desc.b = 0x00409200;
-
 	set_desc_base(&bad_bios_desc, (unsigned long)__va(0x40UL << 4));
 	set_desc_limit(&bad_bios_desc, 4095 - (0x40 << 4));
 	for_each_possible_cpu(i) {

Please also fix this hunk to do the full initialization statically instead of doing some fields statically and some dynamically.

-hpa

Signature · 2 lines

H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

Akinobu Mita

author

2009-08-09 08:04 UTC #3 lore raw

PATCH 1/1 x86: Introduce GDT_ENTRY_INIT(), initialize bad_bios_desc statically

Fully initialize bad_bios_desc statically instead of doing some fields statically and some dynamically.

Signed-off-by Akinobu Mita <[email protected]>

---
 arch/x86/kernel/apm_32.c        |   19 +++++++++----------
 drivers/pnp/pnpbios/bioscalls.c |    5 ++---
 2 files changed, 11 insertions(+), 13 deletions(-)

arch/x86/kernel/apm_32.c +9 ~~-10~~

index bfe0815..151ace6 100644
@@ -403,7 +403,15 @@ static DECLARE_WAIT_QUEUE_HEAD(apm_waitqueue);
 static DECLARE_WAIT_QUEUE_HEAD(apm_suspend_waitqueue);
 static struct apm_user *user_list;
 static DEFINE_SPINLOCK(user_list_lock);
-static struct desc_struct bad_bios_desc = GDT_ENTRY_INIT(0x4092, 0, 0);
+
+/*
+ * Set up a segment that references the real mode segment 0x40
+ * that extends up to the end of page zero (that we have reserved).
+ * This is for buggy BIOS's that refer to (real mode) segment 0x40
+ * even though they are called in protected mode.
+ */
+static struct desc_struct bad_bios_desc = GDT_ENTRY_INIT(0x4092,
+			(unsigned long)__va(0x400UL), PAGE_SIZE - 0x400 - 1);
 
 static const char driver_version[] = "1.16ac";	/* no spaces */

@@ -2332,15 +2340,6 @@ static int __init apm_init(void)
 	pm_flags |= PM_APM;
 
 	/*
-	 * Set up a segment that references the real mode segment 0x40
-	 * that extends up to the end of page zero (that we have reserved).
-	 * This is for buggy BIOS's that refer to (real mode) segment 0x40
-	 * even though they are called in protected mode.
-	 */
-	set_desc_base(&bad_bios_desc, (unsigned long)__va(0x40UL << 4));
-	set_desc_limit(&bad_bios_desc, 4095 - (0x40 << 4));
-
-	/*
 	 * Set up the long jump entry point to the APM BIOS, which is called
 	 * from inline assembly.
 	 */

drivers/pnp/pnpbios/bioscalls.c +2 -3

index bd035e3..fc83783 100644
@@ -60,7 +60,8 @@ do { \
 	set_desc_limit(&gdt[(selname) >> 3], (size) - 1); \
 } while(0)
 
-static struct desc_struct bad_bios_desc = GDT_ENTRY_INIT(0x4092, 0, 0);
+static struct desc_struct bad_bios_desc = GDT_ENTRY_INIT(0x4092,
+			(unsigned long)__va(0x400UL), PAGE_SIZE - 0x400 - 1);
 
 /*
  * At some point we want to use this stack frame pointer to unwind

@@ -476,8 +477,6 @@ void pnpbios_calls_init(union pnp_bios_install_struct *header)
 	pnp_bios_callpoint.offset = header->fields.pm16offset;
 	pnp_bios_callpoint.segment = PNP_CS16;
 
-	set_desc_base(&bad_bios_desc, (unsigned long)__va(0x40UL << 4));
-	set_desc_limit(&bad_bios_desc, 4095 - (0x40 << 4));
 	for_each_possible_cpu(i) {
 		struct desc_struct *gdt = get_cpu_gdt_table(i);
 		if (!gdt)

tip-bot for Akinobu Mita

author

2009-08-10 09:13 UTC #4 lore raw

[tip:x86/asm] x86: Introduce GDT_ENTRY_INIT(), initialize bad_bios_desc statically

Commit-ID:  c7425314c755d5f94da7c978205c85a7c6201212
Gitweb:     http://git.kernel.org/tip/c7425314c755d5f94da7c978205c85a7c6201212
Author:     Akinobu Mita <[email protected]>
AuthorDate: Sun, 9 Aug 2009 17:03:52 +0900
Committer:  Ingo Molnar <[email protected]>
CommitDate: Mon, 10 Aug 2009 11:10:52 +0200

x86: Introduce GDT_ENTRY_INIT(), initialize bad_bios_desc statically

Fully initialize bad_bios_desc statically instead of doing some fields statically and some dynamically.

Signed-off-by Akinobu Mita <[email protected]>

LKML-Reference: <[email protected]>

Signed-off-by Ingo Molnar <[email protected]>

---
 arch/x86/kernel/apm_32.c        |   19 +++++++++----------
 drivers/pnp/pnpbios/bioscalls.c |    5 ++---
 2 files changed, 11 insertions(+), 13 deletions(-)

arch/x86/kernel/apm_32.c +9 ~~-10~~

index febb2da..39a4462 100644
@@ -403,7 +403,15 @@ static DECLARE_WAIT_QUEUE_HEAD(apm_waitqueue);
 static DECLARE_WAIT_QUEUE_HEAD(apm_suspend_waitqueue);
 static struct apm_user *user_list;
 static DEFINE_SPINLOCK(user_list_lock);
-static struct desc_struct bad_bios_desc = GDT_ENTRY_INIT(0x4092, 0, 0);
+
+/*
+ * Set up a segment that references the real mode segment 0x40
+ * that extends up to the end of page zero (that we have reserved).
+ * This is for buggy BIOS's that refer to (real mode) segment 0x40
+ * even though they are called in protected mode.
+ */
+static struct desc_struct bad_bios_desc = GDT_ENTRY_INIT(0x4092,
+			(unsigned long)__va(0x400UL), PAGE_SIZE - 0x400 - 1);
 
 static const char driver_version[] = "1.16ac";	/* no spaces */

@@ -2332,15 +2340,6 @@ static int __init apm_init(void)
 	pm_flags |= PM_APM;
 
 	/*
-	 * Set up a segment that references the real mode segment 0x40
-	 * that extends up to the end of page zero (that we have reserved).
-	 * This is for buggy BIOS's that refer to (real mode) segment 0x40
-	 * even though they are called in protected mode.
-	 */
-	set_desc_base(&bad_bios_desc, (unsigned long)__va(0x40UL << 4));
-	set_desc_limit(&bad_bios_desc, 4095 - (0x40 << 4));
-
-	/*
 	 * Set up the long jump entry point to the APM BIOS, which is called
 	 * from inline assembly.
 	 */

drivers/pnp/pnpbios/bioscalls.c +2 -3

index bd035e3..fc83783 100644
@@ -60,7 +60,8 @@ do { \
 	set_desc_limit(&gdt[(selname) >> 3], (size) - 1); \
 } while(0)
 
-static struct desc_struct bad_bios_desc = GDT_ENTRY_INIT(0x4092, 0, 0);
+static struct desc_struct bad_bios_desc = GDT_ENTRY_INIT(0x4092,
+			(unsigned long)__va(0x400UL), PAGE_SIZE - 0x400 - 1);
 
 /*
  * At some point we want to use this stack frame pointer to unwind

@@ -476,8 +477,6 @@ void pnpbios_calls_init(union pnp_bios_install_struct *header)
 	pnp_bios_callpoint.offset = header->fields.pm16offset;
 	pnp_bios_callpoint.segment = PNP_CS16;
 
-	set_desc_base(&bad_bios_desc, (unsigned long)__va(0x40UL << 4));
-	set_desc_limit(&bad_bios_desc, 4095 - (0x40 << 4));
 	for_each_possible_cpu(i) {
 		struct desc_struct *gdt = get_cpu_gdt_table(i);
 		if (!gdt)