[Xen-devel] Intercepting page access

[HANNAS YAYA Issa <issa.hannasyaya@xxxxxxxxxxx>]

Hi I am working in a research project

I want to incercept pages access by guest virtual machine.
My approach is setting higher priviledge in pages by setting changing 
the user/sypervisor priviledge bit in page table entry associated to 
this page. Here is the piece of code used
void remove_access(l1_pgentry_t *pl1e){
        l1_pgentry_t ol1e;
        l1_pgentry_t nl1e;
        unsigned int  nmfn;
        if(__copy_from_user(&ol1e, pl1e, sizeof(ol1e)) == 0){
                        nl1e = ol1e;
                        nmfn = l1e_get_pfn(ol1e);
                         if(!(l1e_get_flags(ol1e)&_PAGE_GUEST_KERNEL))
                         {
                                l1e_remove_flags(nl1e, _PAGE_USER);
                                if(__copy_to_guest(pl1e, &nl1e, 
sizeof(nl1e)) != 0)
                                        printk("entry cannot be 
copied\n");
                                flush_tlb_all();
                         }
                }else
                        printk("copy from user failed\n");
}

the pointer pl1e is obtained when PTE is updated (in do_mm_update).
in page fault handler (do_page_fault). I reset the access by this code

void reset_access(l1_pgentry_t *pl1e, l1_pgentry_t ol1e)
{
        l1_pgentry_t nl1e = ol1e;
        l1e_add_flags(nl1e, _PAGE_USER);
                __copy_to_guest(pl1e, &nl1e, sizeof(nl1e));
        flush_tlb_all();
        return;
}




but the problem is that my computer crash and it reboots. I don't know 
what is wrong with my code. I spend 2 weeks trying to solve this problem 
but I couldn't. Please I really need your help
Thank you

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