On 08.05.24 04:34, Steven Rostedt wrote:
On Tue, 30 Apr 2024 12:13:51 +0100
Vincent Donnefort <vdonnefort@xxxxxxxxxx> wrote:
+#ifdef CONFIG_MMU
+static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer,
+ struct vm_area_struct *vma)
+{
+ unsigned long nr_subbufs, nr_pages, vma_pages, pgoff = vma->vm_pgoff;
+ unsigned int subbuf_pages, subbuf_order;
+ struct page **pages;
+ int p = 0, s = 0;
+ int err;
+
+ /* Refuse MP_PRIVATE or writable mappings */
+ if (vma->vm_flags & VM_WRITE || vma->vm_flags & VM_EXEC ||
+ !(vma->vm_flags & VM_MAYSHARE))
+ return -EPERM;
+
+ /*
+ * Make sure the mapping cannot become writable later. Also tell the VM
+ * to not touch these pages (VM_DONTCOPY | VM_DONTEXPAND). Finally,
+ * prevent migration, GUP and dump (VM_IO).
+ */
+ vm_flags_mod(vma, VM_DONTCOPY | VM_DONTEXPAND | VM_IO, VM_MAYWRITE);
Do we really need the VM_IO?
When testing this in gdb, I would get:
(gdb) p tmap->map->subbuf_size
Cannot access memory at address 0x7ffff7fc2008
It appears that you can't ptrace IO memory. When I removed that flag,
gdb has no problem reading that memory.
I think we should drop that flag.
Can you send a v23 with that removed, Shuah's update, and also the
change below:
+
+ lockdep_assert_held(&cpu_buffer->mapping_lock);
+
+ subbuf_order = cpu_buffer->buffer->subbuf_order;
+ subbuf_pages = 1 << subbuf_order;
+
+ nr_subbufs = cpu_buffer->nr_pages + 1; /* + reader-subbuf */
+ nr_pages = ((nr_subbufs) << subbuf_order) - pgoff + 1; /* + meta-page */
+
+ vma_pages = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
+ if (!vma_pages || vma_pages > nr_pages)
+ return -EINVAL;
+
+ nr_pages = vma_pages;
+
+ pages = kcalloc(nr_pages, sizeof(*pages), GFP_KERNEL);
+ if (!pages)
+ return -ENOMEM;
+
+ if (!pgoff) {
+ pages[p++] = virt_to_page(cpu_buffer->meta_page);
+
+ /*
+ * TODO: Align sub-buffers on their size, once
+ * vm_insert_pages() supports the zero-page.
+ */
+ } else {
+ /* Skip the meta-page */
+ pgoff--;
+
+ if (pgoff % subbuf_pages) {
+ err = -EINVAL;
+ goto out;
+ }
+
+ s += pgoff / subbuf_pages;
+ }
+
+ while (s < nr_subbufs && p < nr_pages) {
+ struct page *page = virt_to_page(cpu_buffer->subbuf_ids[s]);
+ int off = 0;
+
+ for (; off < (1 << (subbuf_order)); off++, page++) {
+ if (p >= nr_pages)
+ break;
+
+ pages[p++] = page;
+ }
+ s++;
+ }
The above can be made to:
while (p < nr_pages) {
struct page *page;
int off = 0;
if (WARN_ON_ONCE(s >= nr_subbufs))
break;
I'm not particularly happy about us calling vm_insert_pages with NULL
pointers stored in pages.
Should we instead do
if (WARN_ON_ONCE(s >= nr_subbufs)) {
err = -EINVAL;
goto out;
}
?
--
Cheers,
David / dhildenb
