A callback similar to page_mkwrite except it will be called before making ptes that don't point to normal pages writable.
Signed-off-by: Thomas Hellstrom <[email protected]> --- include/linux/mm.h | 9 +++++++++ mm/memory.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++++--- 2 files changed, 58 insertions(+), 3 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 8b6e55e..23d1791 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -212,6 +212,15 @@ struct vm_operations_struct { * writable, if an error is returned it will cause a SIGBUS */ int (*page_mkwrite)(struct vm_area_struct *vma, struct vm_fault *vmf); + /* + * Notification that a previously read-only pfn map is about to become + * writable, Returning VM_FAULT_NOPAGE will cause the fault to be + * retried, + * Returning a VM_FAULT_SIGBUS or VM_FAULT_OOM will propagate the + * error. Returning 0 will make the pfn map writable. + */ + 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 d176154..8ae9a6e 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2584,6 +2584,45 @@ static inline void cow_user_page(struct page *dst, struct page *src, unsigned lo copy_user_highpage(dst, src, va, vma); } +static int prepare_call_pfn_mkwrite(struct vm_area_struct *vma, + unsigned long address, + pte_t *pte, pmd_t *pmd, + spinlock_t *ptl, pte_t orig_pte) +{ + int ret = 0; + struct vm_fault vmf; + struct mm_struct *mm = vma->vm_mm; + + if (!vma->vm_ops || !vma->vm_ops->pfn_mkwrite) + return 0; + + /* + * In general, we can't say anything about the mapping offset + * here, so set it to 0. + */ + vmf.pgoff = 0; + vmf.virtual_address = (void __user *)(address & PAGE_MASK); + vmf.flags = FAULT_FLAG_WRITE | FAULT_FLAG_MKWRITE; + vmf.page = NULL; + pte_unmap_unlock(pte, ptl); + ret = vma->vm_ops->pfn_mkwrite(vma, &vmf); + if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE))) + return ret; + + pte = pte_offset_map_lock(mm, pmd, address, &ptl); + + /* + * Retry the fault if someone updated the pte while we + * dropped the lock. + */ + if (!pte_same(*pte, orig_pte)) { + pte_unmap_unlock(pte, ptl); + return VM_FAULT_NOPAGE; + } + + return 0; +} + /* * 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 @@ -2621,12 +2660,19 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma, * VM_MIXEDMAP !pfn_valid() case * * We should not cow pages in a shared writeable mapping. - * Just mark the pages writable as we can't do any dirty - * accounting on raw pfn maps. + * Optionally call pfn_mkwrite to notify the address + * space that the pte is about to become writeable. */ if ((vma->vm_flags & (VM_WRITE|VM_SHARED)) == - (VM_WRITE|VM_SHARED)) + (VM_WRITE|VM_SHARED)) { + ret = prepare_call_pfn_mkwrite(vma, address, + page_table, pmd, ptl, + orig_pte); + if (ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)) + return ret; + goto reuse; + } goto gotten; } -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
