Re: Help regarding booting application processor

[Swapnil Pimpale]

Thanks for your quick reply.

On Wed, Feb 24, 2010 at 1:00 PM, address@hidden
<address@hidden> wrote:
> On Wed, Feb 24, 2010 at 12:57 AM, Swapnil Pimpale
> <address@hidden> wrote:
>> Hi all,
>>
>>  I am a final year engineering student and I am doing my project in
>> GRUB-1.97~beta4 and Linux Kernel 2.6.24.7.
>>
>>  I am working on Intel Core 2 Duo architecture. I want to boot a
>> separate kernel on the second core.
>>  As of now, I have brought up the halted AP from the GRUB by sending
>> IPIs in the INIT-SIPI-SIPI sequence. I have also allocated a 4KB page
>> below 1MB and asked the AP to jump to that address.
>>
>>  I am trying to put the BSP in while(1) loop and I want the AP to
>> switch from real to protected mode and then jump to start of kernel.
>> But whenever I do a jump to 1MB the system reboots.
>
> Remember that the RAM physical address space is shared between both
> processors.  You'll need to tell Linux not to touch the second core
> and not to touch the memory used by your second OS.  I think you can
> accomplish both of these goals using the right kernel command line.
> Then you'll have to divide up other hardware, like PCI devices, so
> that only one OS accesses any given device.  For example, the second
> OS won't be able to use a hard disk connected to a SATA controller
> visible to the first one.  Especially the second kernel needs to be
> written not to address the PCI bus controller(s), including
> enumeration of bus devices.
>
> If you can't partition the hardware like this then you'll need a
> hypervisor, which uses protected mode to intercept and virtualize
> attempted hardware access from the other OS.
>
I have considered these issues in the design.
>>  I am using the following code as the trampoline code for the AP.
>>
>>  Can someone please let me know what is wrong in the following code.
>
> Probably you've stomped on a shared resource being used by the first
> processor.  Even if you run an infinite while loop on the first core,
> it can still execute interrupt service routines installed by grub (or
> by the second kernel, if not careful about interrupt-processor masks)
> which would access grub global data structures.  If you overwrite
> anything you may end up with a protection fault or invalid instruction
> exception, both of which would probably vector back to BIOS startup
> code.
>
Ok, I will think in this direction. I just wanted to verify whether
the code in the trampoline.S is correct or not.
>>  Awaiting your reply,
>>
>> Thanks,
>> Swapnil Pimpale
>>
>> ----- trampoline.S -----
>> /* Tell GAS to generate 16-bit instructions so that this code works
>>          in real mode. */
>>
>> #include <grub/symbol.h>
>> #include <grub/i386/pc/memory.h>
>>
>>
>> .align 4096
>> .code16
>> FUNCTION(TRAMPOLINE_CODE)
>> initial:
>>
>>       mov     %cs, %ax
>>       mov     %ax, %ds
>>       cli
>>
>>       lidtl   idtdesc - initial
>>       lgdtl   gdtdesc - initial
>>
>>       mov $0x9e00, %bx                   // 9e00 is the cs
>>       shl $4, %ebx
>>       movl $(gdt - initial + 8), %eax
>>       movl %ebx, %eax
>>
>>        mov $0x10, %bx
>>        xor %ecx, %ecx
>>        mov $0xb800, %cx                 // address of video RAM in %cx
>>        shl $4, %ecx
>>        mov $0x0744, %dx                 // for printing D
>>        xor %eax, %eax
>>        pushw %ax
>>        mov $0x08, %ax
>>        pushw %ax
>>        xor %eax, %eax
>>        mov $0x9e00, %ax
>>        shl $4, %eax
>>        add protcseg - initial, %eax
>>        pushl %eax
>>
>>       xor %eax, %eax
>>       movl %cr0, %eax                 // turn on the PE bit
>>       orl $0x1, %eax
>>       movl %eax, %cr0
>>
>>      jmp l1
>>
>> l1:
>>
>>  mov %bx, %ds
>>  mov %dx, (%ecx)                 // Print D
>>  add $2, %ecx
>>  add $1, %dx
>>
>>  ADDR32 ljmpl $0x8,$((protcseg - initial) + (0x9e00 << 4))
>>
>>  .align 256
>>  .code32
>>  protcseg:
>>
>> l3:
>>  mov %dx, (%ecx)
>>
>>  movw %bx, %es
>>  movw %bx, %fs
>>  movw %bx, %gs
>>  movw %bx, %ss
>>
>> l4:
>> // The following is the code used by /loader/i386/linux.c for entering Linux
>>  mov $0x8c000, %esi
>>  xor %ebx, %ebx
>>  mov $0x8c000, %eax
>>  jmp *0x214(%eax)         // System reboots here
>>
>> l5:
>>       jmp l5
>>
>>
>> .p2align 2
>> gdt:
>>       .word   0, 0
>>       .byte   0, 0, 0, 0
>>
>>       .word   0xFFFF, 0
>>       .byte   0, 0x9A, 0xCF, 0
>>
>>       .word   0xFFFF, 0
>>       .byte   0, 0x92, 0xCF, 0
>>
>>       .word   0xFFFF, 0
>>       .byte   0, 0x9E, 0, 0
>>
>>       .word   0xFFFF, 0
>>       .byte   0, 0x92, 0, 0
>>
>> gdtdesc:
>>       .word   0x27
>>       .long   gdt
>>
>> idtdesc:
>>       .word 0
>>       .long 0
>> FUNCTION(TRAMPOLINE_END)
>>
>>
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>>
>
>
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