On Thu, Sep 18, 2025 at 12:45:38PM -0700, Chris Mason wrote: > On Wed, 10 Sep 2025 21:22:11 +0100 Lorenzo Stoakes > <[email protected]> wrote: > > > We can use the mmap insert pages functionality provided for use in > > mmap_prepare to insert the kcov pages as required. > > > > This does necessitate an allocation, but since it's in the mmap path this > > doesn't seem egregious. The allocation/freeing of the pages array is > > handled automatically by vma_desc_set_mixedmap_pages() and the mapping > > logic. > > > > Signed-off-by: Lorenzo Stoakes <[email protected]> > > --- > > kernel/kcov.c | 42 ++++++++++++++++++++++++++---------------- > > 1 file changed, 26 insertions(+), 16 deletions(-) > > > > diff --git a/kernel/kcov.c b/kernel/kcov.c > > index 1d85597057e1..2bcf403e5f6f 100644 > > --- a/kernel/kcov.c > > +++ b/kernel/kcov.c > > @@ -484,31 +484,41 @@ void kcov_task_exit(struct task_struct *t) > > kcov_put(kcov); > > } > > > > -static int kcov_mmap(struct file *filep, struct vm_area_struct *vma) > > +static int kcov_mmap_error(int err) > > +{ > > + pr_warn_once("kcov: vm_insert_page() failed\n"); > > + return err; > > +} > > + > > +static int kcov_mmap_prepare(struct vm_area_desc *desc) > > { > > int res = 0; > > - struct kcov *kcov = vma->vm_file->private_data; > > - unsigned long size, off; > > - struct page *page; > > + struct kcov *kcov = desc->file->private_data; > > + unsigned long size, nr_pages, i; > > + struct page **pages; > > unsigned long flags; > > > > spin_lock_irqsave(&kcov->lock, flags); > > size = kcov->size * sizeof(unsigned long); > > - if (kcov->area == NULL || vma->vm_pgoff != 0 || > > - vma->vm_end - vma->vm_start != size) { > > + if (kcov->area == NULL || desc->pgoff != 0 || > > + vma_desc_size(desc) != size) { > > res = -EINVAL; > > goto exit; > > } > > spin_unlock_irqrestore(&kcov->lock, flags); > > - vm_flags_set(vma, VM_DONTEXPAND); > > - for (off = 0; off < size; off += PAGE_SIZE) { > > - page = vmalloc_to_page(kcov->area + off); > > - res = vm_insert_page(vma, vma->vm_start + off, page); > > - if (res) { > > - pr_warn_once("kcov: vm_insert_page() failed\n"); > > - return res; > > - } > > - } > > + > > + desc->vm_flags |= VM_DONTEXPAND; > > + nr_pages = size >> PAGE_SHIFT; > > + > > + pages = mmap_action_mixedmap_pages(&desc->action, desc->start, > > + nr_pages); > > Hi Lorenzo, > > Not sure if it belongs here before the EINVAL tests, but it looks like > kcov->size doesn't have any page alignment. I think size could be > 4000 bytes other unaligned values, so nr_pages should round up.
Thanks, you may well be right, but but this series has been respun and I no longer touch kcov. :) Am at v4 now - https://lore.kernel.org/linux-mm/[email protected]/ - apologies for the quick turnaround but going to kernel recipes soon and then on vacation so wanted to get this wrapped up! > > -chris Cheers, Lorenzo
