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Paging: self mapping
Posted: Mon Feb 10, 2003 6:08 am
by Whatever5k
I mapped the page directory into itself like this:
Code: Select all
extern addr_t *pdir;
pdir[1023] = pdir | 0x003;
This means that I can access the page directory at address (4GB - 4MB), right? So I use two macros for getting the PTE and PDE of a virtual address. But when I try to access the PDE, I get a page fault:
Code: Select all
#define PG_TABLE_SIZE 4096
#define PTE_SIZE 4
#define PG_DIR_START(0xFFFFFFFF - 0x400000) /* 4GB - 4MB */
#define ADDR_TO_PDE(virt) (PG_DIR_START + (virt >> 22) * PG_TABLE_SIZE)
#define ADDR_TO_PTE(virt) (PG_DIR_START + ((virt >> 12) &0xFFFFF) * PTE_SIZE)
void foo(addr_t virt)
{
addr_t *pde;
pde = (addr_t*) ADDR_TO_PDE(virt);
if ((*pde & IS_PRESENT) == 0) /* that's where I get the page fault */
...
...
}
Any idea what might be wrong?
Re:Paging: self mapping
Posted: Mon Feb 10, 2003 9:20 am
by Pype.Clicker
did you flush the Translation Lookaside Buffers after you set up your page directory entries ?
i think your "PDE" macro is wrong.
*pde(virt) should refer to the page directory entry for VIRT, right ? this is (imho) located at PG_DIR_START + 1023*PG_TABLE_SIZE + (virt>>22)*PTE_SIZE, not where you set it
Re:Paging: self mapping
Posted: Mon Feb 10, 2003 9:41 am
by Whatever5k
did you flush the Translation Lookaside Buffers after you set up your page directory entries ?
Not really...how would I do this, how would I flush the whole TLB...I saw different ways...which is the right and common one?
*pde(virt) should refer to the page directory entry for VIRT, right ?
Well, it should return the virtual address of the PDE, yes...
Re:Paging: self mapping
Posted: Mon Feb 10, 2003 10:19 am
by Whatever5k
Alright, I flush the TLB by moving cr3 to eax and eax back to cr3...
Now after setting up the self mapping and enabling paging, I flush the TLB...but it still doesn't work...neither with your version of ADDR_TO_PDE