On Tue, Jul 12, 2016 at 09:31:30AM +0800, Xishi Qiu wrote: > On 2016/7/11 21:30, Kirill A. Shutemov wrote: > > > On Mon, Jul 11, 2016 at 06:12:30PM +0800, Xishi Qiu wrote: > >> Hi, > >> > >> We can use mprotect to set read only or read/write. > >> > >> mprotect_fixup() > >> vma_set_page_prot() > >> vm_pgprot_modify() > >> vm_get_page_prot() > >> protection_map[vm_flags & > >> (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)] > >> > >> The following code shows that prots from __P001(PROT_READ) and > >> __P010(PROT_WRITE) > >> are the same, so how does it distinguish read only or read/write from > >> mprotect? > > > > It doesn't. > > > > Write protection will be removed by fault handler on next write access to > > the page. Somewhat suboptiomal, but zero page implemenation relies on this > > to work properly. > > > > Hi Kirill, > > I know, PAGE_READONLY and PAGE_COPY are both missed _PAGE_RW, > so it will cause page fault, then we will set new prot flag from > vma, right?
Yes. See wp_page_reuse(). -- Kirill A. Shutemov
