Hi Oleg,
Thanks for your kind review!
> On Jun 5, 2019, at 3:02 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
>
> On 06/04, Song Liu wrote:
>>
>> Currently, uprobe swaps the target page with a anonymous page in both
>> install_breakpoint() and remove_breakpoint(). When all uprobes on a page
>> are removed, the given mm is still using an anonymous page (not the
>> original page).
>
> Agreed, it would be nice to avoid this,
>
>> @@ -461,9 +471,10 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
>> unsigned long vaddr, uprobe_opcode_t opcode)
>> {
>> struct uprobe *uprobe;
>> - struct page *old_page, *new_page;
>> + struct page *old_page, *new_page, *orig_page = NULL;
>> struct vm_area_struct *vma;
>> int ret, is_register, ref_ctr_updated = 0;
>> + pgoff_t index;
>>
>> is_register = is_swbp_insn(&opcode);
>> uprobe = container_of(auprobe, struct uprobe, arch);
>> @@ -501,6 +512,19 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
>> copy_highpage(new_page, old_page);
>> copy_to_page(new_page, vaddr, &opcode, UPROBE_SWBP_INSN_SIZE);
>>
>> + index = vaddr_to_offset(vma, vaddr & PAGE_MASK) >> PAGE_SHIFT;
>> + orig_page = find_get_page(vma->vm_file->f_inode->i_mapping, index);
>
> I think you should take is_register into account, if it is true we are going
> to install the breakpoint so we can avoid find_get_page/pages_identical.
Good idea! I will add this to v3.
>
>> + if (orig_page) {
>> + if (pages_identical(new_page, orig_page)) {
>> + /* if new_page matches orig_page, use orig_page */
>> + put_page(new_page);
>> + new_page = orig_page;
>
> Hmm. can't we simply unmap the page in this case?
I haven't found an easier way here. I tried with zap_vma_ptes() and
unmap_page_range(). But neither of them works well here.
Also, we need to deal with *_mm_counter, rmap, etc. So I guess reusing
__replace_page() (as current patch) is probably the easiest solution.
Did I miss anything?
Thanks again,
Song
