On Tue, Nov 20, 2012 at 06:00:40PM +0200, Kirill A. Shutemov wrote: > On Fri, Nov 16, 2012 at 12:10:39PM -0800, David Rientjes wrote: > > On Fri, 16 Nov 2012, Kirill A. Shutemov wrote: > > > > > > > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > > > > > > index d767a7c..05490b3 100644 > > > > > > > --- a/mm/huge_memory.c > > > > > > > +++ b/mm/huge_memory.c > > > > > > > @@ -1259,6 +1259,8 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > > > > > > > pmd_t entry; > > > > > > > entry = pmdp_get_and_clear(mm, addr, pmd); > > > > > > > entry = pmd_modify(entry, newprot); > > > > > > > + if (is_huge_zero_pmd(entry)) > > > > > > > + entry = pmd_wrprotect(entry); > > > > > > > set_pmd_at(mm, addr, pmd, entry); > > > > > > > spin_unlock(&vma->vm_mm->page_table_lock); > > > > > > > ret = 1; > > > > > > > > > > > > Nack, this should be handled in pmd_modify(). > > > > > > > > > > I disagree. It means we will have to enable hzp per arch. Bad idea. > > > > > > > > > > > > > pmd_modify() only exists for those architectures with thp support already, > > > > so you've already implicitly enabled for all the necessary architectures > > > > with your patchset. > > > > > > Now we have huge zero page fully implemented inside mm/huge_memory.c. Push > > > this logic to pmd_modify() means we expose hzp implementation details to > > > arch code. Looks ugly for me. > > > > > > > So you are suggesting that anybody who ever does pmd_modify() in the > > future is responsible for knowing about the zero page and to protect > > against giving it write permission in the calling code?? > > Looks like we don't need the patch at all. > > IIUC, if you ask for PROT_WRITE vm_get_page_prot() will translate it to > _PAGE_COPY or similar and you'll only get the page writable on pagefault. > > Could anybody confirm that it's correct? > > -- > Kirill A. Shutemov Andrew, please drop the patch or replace it with the patch below, if you wish. From 048e3d4c97202cfecab55ead2a816421dce4b382 Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> Date: Tue, 7 Aug 2012 06:09:56 -0700 Subject: [PATCH] thp: change_huge_pmd(): make sure we don't try to make a page writable mprotect core never tries to make page writable using change_huge_pmd(). Let's add an assert that the assumption is true. It's important to be sure we will not make huge zero page writable. Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> --- mm/huge_memory.c | 1 + 1 file changed, 1 insertion(+) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index f5589c0..5fba83b 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1245,6 +1245,7 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, pmd_t entry; entry = pmdp_get_and_clear(mm, addr, pmd); entry = pmd_modify(entry, newprot); + BUG_ON(pmd_write(entry)); set_pmd_at(mm, addr, pmd, entry); spin_unlock(&vma->vm_mm->page_table_lock); ret = 1; -- Kirill A. Shutemov
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