[Xen-devel] put_page in ptwr_do_page_fault

[Xinxin Jin <xinxinjin89@xxxxxxxxx>]

Hi all,

I am trying to understand write page table handler for PV guests. I got the core of ptwr_do_page_fault is x86_emulate() which will emulate the write operation in Xen. But why after that Xen calls  put_page() to free the page mapped to the PTE ? The code snapshot is as follows: 

int ptwr_do_page_fault(struct vcpu *v, unsigned long addr,

                       struct cpu_user_regs *regs)

{

    struct domain *d = v->domain;

    struct page_info *page;

    l1_pgentry_t      pte;

    struct ptwr_emulate_ctxt ptwr_ctxt;

    int rc;

    /* Attempt to read the PTE that maps the VA being accessed. */

    guest_get_eff_l1e(v, addr, &pte);

    ......

    page = l1e_get_page(pte); 

    

    ......

    rc = x86_emulate(&ptwr_ctxt.ctxt, &ptwr_emulate_ops);

  

    page_unlock(page);

    put_page(page);

    ......

}

Thanks a lot,

-- 
Xinxin

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel