2005-04-08 16:14:58

by Juerg Billeter

Subject: [PATCH] Fix reloading GDT on ACPI S3 wakeup

Hi

This patch - based on
http://marc.theaimsgroup.com/?l=linux-kernel&m=110055503031009&w=2 -
makes ACPI S3 wakeup work for me on a ThinkPad T40p laptop with a SMP
kernel. Without it only UP kernels work. I've been using the patch for
three months now without any issues.

The ACPI resume code currently uses a real-mode 16-bit lgdt instruction
to reload the GDT. This only restores the lower 24 bits of the GDT base
address. In recent SMP kernels, the GDT seems to have moved out of the
lower 16 megs, thereby causing the ACPI resume to fail -- an invalid GDT
was being loaded.

Regards,

Juerg

--
Signed-off-by: Juerg Billeter <[email protected]>

diff -uNr linux-2.6.10.orig/arch/i386/kernel/acpi/wakeup.S linux-2.6.10/arch/i386/kernel/acpi/wakeup.S
--- linux-2.6.10.orig/arch/i386/kernel/acpi/wakeup.S 2004-12-24 22:34:26.000000000 +0100
+++ linux-2.6.10/arch/i386/kernel/acpi/wakeup.S 2005-01-08 23:34:38.551471486 +0100
@@ -74,8 +74,9 @@
movw %ax,%fs
movw $0x0e00 + 'i', %fs:(0x12)

- # need a gdt
- lgdt real_save_gdt - wakeup_code
+ # need a gdt -- use lgdtl to force 32-bit operands, in case
+ # the GDT is located past 16 megabytes
+ lgdtl real_save_gdt - wakeup_code

movl real_save_cr0 - wakeup_code, %eax
movl %eax, %cr0

2005-04-11 17:18:01

by Brown, Len

Subject: Re: [PATCH] Fix reloading GDT on ACPI S3 wakeup

I've applied Nickolai's patch -- thanks for the ping.

-Len

On Fri, 2005-04-08 at 12:14, Juerg Billeter wrote:
> Hi
>
> This patch - based on
> http://marc.theaimsgroup.com/?l=linux-kernel&m=110055503031009&w=2 -
> makes ACPI S3 wakeup work for me on a ThinkPad T40p laptop with a SMP
> kernel. Without it only UP kernels work. I've been using the patch for
> three months now without any issues.
>
> The ACPI resume code currently uses a real-mode 16-bit lgdt
> instruction
> to reload the GDT. This only restores the lower 24 bits of the GDT
> base
> address. In recent SMP kernels, the GDT seems to have moved out of
> the
> lower 16 megs, thereby causing the ACPI resume to fail -- an invalid
> GDT
> was being loaded.
>
> Regards,
>
> Juerg
>
> --
> Signed-off-by: Juerg Billeter <[email protected]>
>
> diff -uNr linux-2.6.10.orig/arch/i386/kernel/acpi/wakeup.S
> linux-2.6.10/arch/i386/kernel/acpi/wakeup.S
> --- linux-2.6.10.orig/arch/i386/kernel/acpi/wakeup.S 2004-12-24
> 22:34:26.000000000 +0100
> +++ linux-2.6.10/arch/i386/kernel/acpi/wakeup.S 2005-01-08
> 23:34:38.551471486 +0100
> @@ -74,8 +74,9 @@
> movw %ax,%fs
> movw $0x0e00 + 'i', %fs:(0x12)
>
> - # need a gdt
> - lgdt real_save_gdt - wakeup_code
> + # need a gdt -- use lgdtl to force 32-bit operands, in case
> + # the GDT is located past 16 megabytes
> + lgdtl real_save_gdt - wakeup_code
>
> movl real_save_cr0 - wakeup_code, %eax
> movl %eax, %cr0
>
>
>
>