mm/swapfile: skip HugeTLB pages for unuse_vma

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: mm/swapfile: skip HugeTLB pages for unuse_vma I got a bad pud error and lost a 1GB HugeTLB when calling swapoff. The problem can be reproduced by the following steps: 1. Allocate an anonymous 1GB HugeTLB and some other anonymous memory. 2. Swapout the above anonymous memory. 3. run swapoff and we will get a bad pud error in kernel message: mm/pgtable-generic.c:42: bad pud 00000000743d215d(84000001400000e7) We can tell that pud_clear_bad is called by pud_none_or_clear_bad in unuse_pud_range() by ftrace. And therefore the HugeTLB pages will never be freed because we lost it from page table. We can skip HugeTLB pages for unuse_vma to fix it.

References

• https://git.kernel.org/stable/c/ba7f982cdb37ff5a7739dec85d7325ea66fc1496
• https://git.kernel.org/stable/c/417d5838ca73c6331ae2fe692fab6c25c00d9a0b
• https://git.kernel.org/stable/c/e41710f5a61aca9d6baaa8f53908a927dd9e7aa7
• https://git.kernel.org/stable/c/6ec0fe3756f941f42f8c57156b8bdf2877b2ebaf
• https://git.kernel.org/stable/c/bed2b9037806c62166a0ef9a559a1e7e3e1275b8
• https://git.kernel.org/stable/c/eb66a833cdd2f7302ee05d05e0fa12a2ca32eb87
• https://git.kernel.org/stable/c/7528c4fb1237512ee18049f852f014eba80bbe8d