Re: [Xen-devel] How works Xen mmu ?

[Sylvestre Gallon <syl@xxxxxxxxx>]

On Thu, Jun 3, 2010 at 3:29 PM, Keir Fraser <keir.fraser@xxxxxxxxxxxxx> wrote:
>
>
>
> On 03/06/2010 14:16, "Sylvestre Gallon" <syl@xxxxxxxxx> wrote:
>
>> addr = get_cr3();                     // getting page directory
>> addr &= 0xfffff000;                   // remove pdir flags
>> addr = ((uint32_t*) addr_[0];     // get address of first page dir
>> (0xb8000 is in the first pdir)
>> addr += 0xb8 * 4;                    // 0xb8000 must be the pte 0xb8 into 
>> pdir
>> 0
>>
>> mmu.ptr = pte | MMU_NORMAL_PT_UPDATE;
>> mmu.val = 0xb8000 | 0x3;        // 0x3 for pte present and rw flags
>>
>> HYPERVISOR_mmu_update(&mmu, 1, NULL, DOMID_SELF);
>>
>> while(42);
>>
>> But when I try this code I get an unhandled page fault :/
>>
>> Do I have misunderstood something ?
>
> This is closer, but page table entries will be 64 bits not 32 bits (hence
> use uint64_t). And also the page tables will have three or four levels
> (depending on whether your guest is 32-bit PAE or 64-bit). So in the 64-bit
> case for example, you would read cr3 to get pagedir_1, then index into
> pagedir_1 to get pagedir_2, then index into pagedir_2 to get pagedir_3, then
> index into pagedir_3 to get the pagetable. And mmu.ptr would point at an
> entry in that pagetable.
>

OK , I see.

I still have a question, does I need to compile my kernel with -m64 ?

If not how can I use 64bits addresses ?

Thanks for your help.

Cheers,
-- 
Sylvestre Gallon

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