On Wed, Nov 16, 2022 at 5:36 PM Luis Chamberlain <mcgrof@xxxxxxxxxx> wrote:
>
> On Wed, Nov 16, 2022 at 05:06:16PM -0800, Song Liu wrote:
> > +static void move_vmap_to_free_text_tree(void *addr)
> > +{
> > + struct vmap_area *va;
> > +
> > + /* remove from vmap_area_root */
> > + spin_lock(&vmap_area_lock);
> > + va = __find_vmap_area((unsigned long)addr, &vmap_area_root);
> > + if (WARN_ON_ONCE(!va)) {
> > + spin_unlock(&vmap_area_lock);
> > + return;
> > + }
> > + unlink_va(va, &vmap_area_root);
> > + spin_unlock(&vmap_area_lock);
> > +
> > + /* make the memory RO+X */
> > + memset(addr, 0, va->va_end - va->va_start);
> > + set_memory_ro(va->va_start, (va->va_end - va->va_start) >> PAGE_SHIFT);
> > + set_memory_x(va->va_start, (va->va_end - va->va_start) >> PAGE_SHIFT);
> > +
> > + /* add to all_text_vm */
> > + va->vm->next = all_text_vm;
> > + all_text_vm = va->vm;
> > +
> > + /* add to free_text_area_root */
> > + spin_lock(&free_text_area_lock);
> > + merge_or_add_vmap_area_augment(va, &free_text_area_root, &free_text_area_list);
> > + spin_unlock(&free_text_area_lock);
> > +}
>
> <-- snip -->
>
> > +void *execmem_alloc(unsigned long size, unsigned long align)
> > +{
> > + struct vmap_area *va, *tmp;
> > + unsigned long addr;
> > + enum fit_type type;
> > + int ret;
> > +
> > + va = kmem_cache_alloc_node(vmap_area_cachep, GFP_KERNEL, NUMA_NO_NODE);
> > + if (unlikely(!va))
> > + return NULL;
> > +
> > +again:
> > + preload_this_cpu_lock(&free_text_area_lock, GFP_KERNEL, NUMA_NO_NODE);
> > + tmp = find_vmap_lowest_match(&free_text_area_root, size, align, 1, false);
> > +
> > + if (!tmp) {
> > + unsigned long alloc_size;
> > + void *ptr;
> > +
> > + spin_unlock(&free_text_area_lock);
> > +
> > + /*
> > + * Not enough continuous space in free_text_area_root, try
> > + * allocate more memory. The memory is first added to
> > + * vmap_area_root, and then moved to free_text_area_root.
> > + */
> > + alloc_size = roundup(size, PMD_SIZE * num_online_nodes());
> > + ptr = __vmalloc_node_range(alloc_size, PMD_SIZE, EXEC_MEM_START,
> > + EXEC_MEM_END, GFP_KERNEL, PAGE_KERNEL,
> > + VM_ALLOW_HUGE_VMAP | VM_NO_GUARD,
> > + NUMA_NO_NODE, __builtin_return_address(0));
> > + if (unlikely(!ptr))
> > + goto err_out;
> > +
> > + move_vmap_to_free_text_tree(ptr);
>
> It's not perfectly clear to me how we know for sure nothing can take
> this underneath our noses.
This is because ptr points to vmap_area in vmap_area_* tree. It is only
used by the user (this thread). It is like we know vmalloc memory will
not go away until we call vfree on it.
Does this make sense?
Song
