| Message ID | 55100BDC.7000901@plexistor.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, 23 Mar 2015 14:49:32 +0200 Boaz Harrosh <boaz@plexistor.com> wrote: > From: Yigal Korman <yigal@plexistor.com> > > This will allow FS that uses VM_PFNMAP | VM_MIXEDMAP (no page structs) > to get notified when access is a write to a read-only PFN. > > This can happen if we mmap() a file then first mmap-read from it > to page-in a read-only PFN, than we mmap-write to the same page. > > We need this functionality to fix a DAX bug, where in the scenario > above we fail to set ctime/mtime though we modified the file. > An xfstest is attached to this patchset that shows the failure > and the fix. (A DAX patch will follow) > > This functionality is extra important for us, because upon > dirtying of a pmem page we also want to RDMA the page to a > remote cluster node. > > We define a new pfn_mkwrite and do not reuse page_mkwrite because > 1 - The name ;-) > 2 - But mainly because it would take a very long and tedious > audit of all page_mkwrite functions of VM_MIXEDMAP/VM_PFNMAP > users. To make sure they do not now CRASH. For example current > DAX code (which this is for) would crash. > If we would want to reuse page_mkwrite, We will need to first > patch all users, so to not-crash-on-no-page. Then enable this > patch. But even if I did that I would not sleep so well at night. > Adding a new vector is the safest thing to do, and is not that > expensive. an extra pointer at a static function vector per driver. > Also the new vector is better for performance, because else we > Will call all current Kernel vectors, so to: > check-ha-no-page-do-nothing and return. > > No need to call it from do_shared_fault because do_wp_page is called to > change pte permissions anyway. Looks OK to me. > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -1982,6 +1982,22 @@ static int do_page_mkwrite(struct vm_area_struct *vma, struct page *page, > return ret; > } > > +static int do_pfn_mkwrite(struct vm_area_struct *vma, unsigned long address) > +{ > + struct vm_fault vmf; > + > + if (!vma->vm_ops || !vma->vm_ops->pfn_mkwrite) > + return 0; > + > + vmf.page = 0; > + vmf.pgoff = (((address & PAGE_MASK) - vma->vm_start) >> PAGE_SHIFT) + > + vma->vm_pgoff; > + vmf.virtual_address = (void __user *)(address & PAGE_MASK); > + vmf.flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE; > + > + return vma->vm_ops->pfn_mkwrite(vma, &vmf); > +} It might be a little neater to use if (vma->vm_ops && vma->vm_ops->pfn_mkwrite) { struct vm_fault vmf = { ... }; ... } > /* > * This routine handles present pages, when users try to write > * to a shared page. It is done by copying the page to a new address > @@ -2025,8 +2041,17 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma, > * accounting on raw pfn maps. > */ > if ((vma->vm_flags & (VM_WRITE|VM_SHARED)) == > - (VM_WRITE|VM_SHARED)) > + (VM_WRITE|VM_SHARED)) { > + pte_unmap_unlock(page_table, ptl); > + ret = do_pfn_mkwrite(vma, address); > + if (ret & VM_FAULT_ERROR) > + return ret; > + page_table = pte_offset_map_lock(mm, pmd, address, > + &ptl); > + if (!pte_same(*page_table, orig_pte)) > + goto unlock; > goto reuse; > + } > goto gotten; There are significant pending changes in this area. See linux-next, or http://ozlabs.org/~akpm/mmots/broken-out/mm-refactor-*
diff --git a/include/linux/mm.h b/include/linux/mm.h index 47a9392..1cd820c 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -250,6 +250,8 @@ struct vm_operations_struct { /* notification that a previously read-only page is about to become * writable, if an error is returned it will cause a SIGBUS */ int (*page_mkwrite)(struct vm_area_struct *vma, struct vm_fault *vmf); + /* same as page_mkwrite when using VM_PFNMAP|VM_MIXEDMAP */ + int (*pfn_mkwrite)(struct vm_area_struct *vma, struct vm_fault *vmf); /* called by access_process_vm when get_user_pages() fails, typically * for use by special VMAs that can switch between memory and hardware diff --git a/mm/memory.c b/mm/memory.c index 8068893..ebef8f6 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1982,6 +1982,22 @@ static int do_page_mkwrite(struct vm_area_struct *vma, struct page *page, return ret; } +static int do_pfn_mkwrite(struct vm_area_struct *vma, unsigned long address) +{ + struct vm_fault vmf; + + if (!vma->vm_ops || !vma->vm_ops->pfn_mkwrite) + return 0; + + vmf.page = 0; + vmf.pgoff = (((address & PAGE_MASK) - vma->vm_start) >> PAGE_SHIFT) + + vma->vm_pgoff; + vmf.virtual_address = (void __user *)(address & PAGE_MASK); + vmf.flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE; + + return vma->vm_ops->pfn_mkwrite(vma, &vmf); +} + /* * This routine handles present pages, when users try to write * to a shared page. It is done by copying the page to a new address @@ -2025,8 +2041,17 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma, * accounting on raw pfn maps. */ if ((vma->vm_flags & (VM_WRITE|VM_SHARED)) == - (VM_WRITE|VM_SHARED)) + (VM_WRITE|VM_SHARED)) { + pte_unmap_unlock(page_table, ptl); + ret = do_pfn_mkwrite(vma, address); + if (ret & VM_FAULT_ERROR) + return ret; + page_table = pte_offset_map_lock(mm, pmd, address, + &ptl); + if (!pte_same(*page_table, orig_pte)) + goto unlock; goto reuse; + } goto gotten; }