Re: [PATCH v10 1/5] kasan: support backing vmalloc space with real shadow memory

Uladzislau Rezki
2019-10-30T14:30:04Z

Hello, Daniel

>
> @@ -1294,14 +1299,19 @@ static bool __purge_vmap_area_lazy(unsigned long start, unsigned long end)
> spin_lock(&free_vmap_area_lock);
> llist_for_each_entry_safe(va, n_va, valist, purge_list) {
> unsigned long nr = (va->va_end - va->va_start) >> PAGE_SHIFT;
> + unsigned long orig_start = va->va_start;
> + unsigned long orig_end = va->va_end;
>
> /*
> * Finally insert or merge lazily-freed area. It is
> * detached and there is no need to "unlink" it from
> * anything.
> */
> - merge_or_add_vmap_area(va,
> - &free_vmap_area_root, &free_vmap_area_list);
> + va = merge_or_add_vmap_area(va, &free_vmap_area_root,
> + &free_vmap_area_list);
> +
> + kasan_release_vmalloc(orig_start, orig_end,
> + va->va_start, va->va_end);
>
I have some questions here. I have not analyzed kasan_releace_vmalloc()
logic in detail, sorry for that if i miss something. __purge_vmap_area_lazy()
deals with big address space, so not only vmalloc addresses it frees here,
basically it can be any, starting from 1 until ULONG_MAX, whereas vmalloc
space spans from VMALLOC_START - VMALLOC_END:

1) Should it be checked that vmalloc only address is freed or you handle
it somewhere else?

if (is_vmalloc_addr(va->va_start))
kasan_release_vmalloc(...)

2) Have you run any bencmarking just to see how much overhead it adds?
I am asking, because probably it make sense to add those figures to the
backlog(commit message). For example you can run:

<snip>
sudo ./test_vmalloc.sh performance
and
sudo ./test_vmalloc.sh sequential_test_order=1
<snip>

Thanks!

--
Vlad Rezki