On Wed, Jan 29, 2025 at 12:53:59PM +0100, David Hildenbrand wrote:
We only have two FOLL_SPLIT_PMD users. While uprobe refuses hugetlb early, make_device_exclusive_range() can end up getting called on hugetlb VMAs.
Right now, this means that with a PMD-sized hugetlb page, we can end up calling split_huge_pmd(), because pmd_trans_huge() also succeeds with hugetlb PMDs.
For example, using a modified hmm-test selftest one can trigger:
I haven't explicitly tested this with nouveau but I can't see anything that would prevent this being called on a hugetlb vma there either.
Reviewed-by: Alistair Popple apopple@nvidia.com
[ 207.017134][T14945] ------------[ cut here ]------------ [ 207.018614][T14945] kernel BUG at mm/page_table_check.c:87! [ 207.019716][T14945] Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN NOPTI [ 207.021072][T14945] CPU: 3 UID: 0 PID: ... [ 207.023036][T14945] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-2.fc40 04/01/2014 [ 207.024834][T14945] RIP: 0010:page_table_check_clear.part.0+0x488/0x510 [ 207.026128][T14945] Code: ... [ 207.029965][T14945] RSP: 0018:ffffc9000cb8f348 EFLAGS: 00010293 [ 207.031139][T14945] RAX: 0000000000000000 RBX: 00000000ffffffff RCX: ffffffff8249a0cd [ 207.032649][T14945] RDX: ffff88811e883c80 RSI: ffffffff8249a357 RDI: ffff88811e883c80 [ 207.034183][T14945] RBP: ffff888105c0a050 R08: 0000000000000005 R09: 0000000000000000 [ 207.035688][T14945] R10: 00000000ffffffff R11: 0000000000000003 R12: 0000000000000001 [ 207.037203][T14945] R13: 0000000000000200 R14: 0000000000000001 R15: dffffc0000000000 [ 207.038711][T14945] FS: 00007f2783275740(0000) GS:ffff8881f4980000(0000) knlGS:0000000000000000 [ 207.040407][T14945] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 207.041660][T14945] CR2: 00007f2782c00000 CR3: 0000000132356000 CR4: 0000000000750ef0 [ 207.043196][T14945] PKRU: 55555554 [ 207.043880][T14945] Call Trace: [ 207.044506][T14945] <TASK> [ 207.045086][T14945] ? __die+0x51/0x92 [ 207.045864][T14945] ? die+0x29/0x50 [ 207.046596][T14945] ? do_trap+0x250/0x320 [ 207.047430][T14945] ? do_error_trap+0xe7/0x220 [ 207.048346][T14945] ? page_table_check_clear.part.0+0x488/0x510 [ 207.049535][T14945] ? handle_invalid_op+0x34/0x40 [ 207.050494][T14945] ? page_table_check_clear.part.0+0x488/0x510 [ 207.051681][T14945] ? exc_invalid_op+0x2e/0x50 [ 207.052589][T14945] ? asm_exc_invalid_op+0x1a/0x20 [ 207.053596][T14945] ? page_table_check_clear.part.0+0x1fd/0x510 [ 207.054790][T14945] ? page_table_check_clear.part.0+0x487/0x510 [ 207.055993][T14945] ? page_table_check_clear.part.0+0x488/0x510 [ 207.057195][T14945] ? page_table_check_clear.part.0+0x487/0x510 [ 207.058384][T14945] __page_table_check_pmd_clear+0x34b/0x5a0 [ 207.059524][T14945] ? __pfx___page_table_check_pmd_clear+0x10/0x10 [ 207.060775][T14945] ? __pfx___mutex_unlock_slowpath+0x10/0x10 [ 207.061940][T14945] ? __pfx___lock_acquire+0x10/0x10 [ 207.062967][T14945] pmdp_huge_clear_flush+0x279/0x360 [ 207.064024][T14945] split_huge_pmd_locked+0x82b/0x3750 ...
Before commit 9cb28da54643 ("mm/gup: handle hugetlb in the generic follow_page_mask code"), we would have ignored the flag; instead, let's simply refuse the combination completely in check_vma_flags(): the caller is likely not prepared to handle any hugetlb folios.
We'll teach make_device_exclusive_range() separately to ignore any hugetlb folios as a future-proof safety net.
Fixes: 9cb28da54643 ("mm/gup: handle hugetlb in the generic follow_page_mask code") Cc: stable@vger.kernel.org Signed-off-by: David Hildenbrand david@redhat.com
mm/gup.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/mm/gup.c b/mm/gup.c index 3883b307780e..61e751baf862 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1283,6 +1283,9 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags) if ((gup_flags & FOLL_LONGTERM) && vma_is_fsdax(vma)) return -EOPNOTSUPP;
- if ((gup_flags & FOLL_SPLIT_PMD) && is_vm_hugetlb_page(vma))
return -EOPNOTSUPP;- if (vma_is_secretmem(vma)) return -EFAULT;
2.48.1