Hi,
I am experimenting with page table walking. I run a user space
program and mmap a memory region and pass the address to the module.
In the kernel module I get the current->mm to get the current task
memory descriptor and use it to walk the pages. Once I get the pte
address I reboot and dump the memory at that point using u-boot. (md.b
<addr> 1)
but I do not find the values present there. ( I have filled the region
with incremental value starting from 0 to 255).
My processor is a Samsung S3C2440 ARM920T (mini2440 development
board). The physical address starts at 0x30000000.
-------------------------------------------------------------------
Sample code of the page walk: (This is just for illustration and
experimenting and does
not contain error checks etc.).
void my_follow_page(struct mm_struct *mm,
unsigned long addr_res)
{
pgd_t *pgd;
pmd_t *pmd;
pud_t *pud;
pte_t *ptep, pte;
struct page *page;
down_read(&(mm->mmap_sem));
pgd = pgd_offset(mm,addr_res);
if(pgd_none(*pgd) || pgd_bad(*pgd)) {
printk(KERN_ALERT "pgd bad\n");
return;
} else {
printk(KERN_ALERT "pgd 0x%lx\n",(unsigned long)pgd);
}
pud = pud_offset(pgd,addr_res);
if(pud_none(*pud) || pud_bad(*pud)) {
printk(KERN_ALERT "pud bad\n");
return;
} else {
printk(KERN_ALERT "pud 0x%lx\n",(unsigned long)pud);
}
pmd = pmd_offset(pud,addr_res);
if(pmd_none(*pmd) || pmd_bad(*pmd)) {
printk(KERN_ALERT "pmd bad\n");
return;
} else {
printk(KERN_ALERT "pmd 0x%lx\n",(unsigned long)pmd);
}
ptep = pte_offset_map(pmd,addr_res);
if(!ptep) {
printk(KERN_ALERT "ptep bad\n");
} else {
printk(KERN_ALERT "ptep 0x%lx\n",(unsigned long)ptep);
}
pte = *ptep;
if(pte_present(pte)) {
printk(KERN_ALERT "pte : 0x%lx\n",(unsigned long)pte);
page = pte_page(pte);
} else {
printk(KERN_ALERT "pte not present\n");
}
printk(KERN_ALERT "pte with offset 0x%lx offset : 0x%lx\n",
pte+((addr_res) & ((1<<PAGE_SHIFT)-1)),
addr_res & ((1<<PAGE_SHIFT)-1));
up_read(&(mm->mmap_sem));
}
-------------------------------------------------------------------
Sample output:
[ 86.447788] Current task pid: 2384
[ 86.447885] mm: 0xc3b39a80, active_mm 0xc3b39a80
[ 86.451594] Page global directory : 0xc3af4000
[ 86.456127] mmap base : 0xb6f60000
[ 86.459175] vm_start : 0x8000, vm_end : 0x9000
[ 86.463684] vm_start : 0x10000, vm_end : 0x11000
[ 86.468202] vm_start : 0x100000, vm_end : 0x101000
[ 86.472884] vm_start : 0xb6dfc000, vm_end : 0xb6f25000
[ 86.477975] vm_start : 0xb6f25000, vm_end : 0xb6f2c000
[ 86.483000] vm_start : 0xb6f2c000, vm_end : 0xb6f2e000
[ 86.488070] vm_start : 0xb6f2e000, vm_end : 0xb6f2f000
[ 86.493080] vm_start : 0xb6f2f000, vm_end : 0xb6f32000
[ 86.498089] vm_start : 0xb6f3a000, vm_end : 0xb6f57000
[ 86.503120] vm_start : 0xb6f5a000, vm_end : 0xb6f5d000
[ 86.508149] vm_start : 0xb6f5d000, vm_end : 0xb6f5e000
[ 86.513187] vm_start : 0xb6f5e000, vm_end : 0xb6f5f000
[ 86.518225] vm_start : 0xb6f5f000, vm_end : 0xb6f60000
[ 86.523251] vm_start : 0xbe934000, vm_end : 0xbe956000
[ 86.528299] kval : 3020100
[ 86.530870] addr: 100000
[ 86.533446] pgd 0xc3af4000
[ 86.535992] pud 0xc3af4000
[ 86.538720] pmd 0xc3af4000
[ 86.541281] ptep 0xc3b0e400
[ 86.544071] pte : 0x3278214f
[ 86.546831] pte with offset 0x3278214f offset : 0x0
The problem is that when I do a md.b 0x3278214f 100 in u-boot to do a
memory dump I see the values in it but I don't see the exact value
filled in that memory location. What am I doing wrong?
Thanks,
Gautam.
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