On Thu, 25 Jul 2024 10:03:45 +0100, Will Deacon wrote:
Lina reports random oopsen originating from the fast GUP code when 16K pages are used with 4-level page-tables, the fourth level being folded at runtime due to lack of LPA2.
In this configuration, the generic implementation of p4d_offset_lockless() will return a 'p4d_t *' corresponding to the 'pgd_t' allocated on the stack of the caller, gup_fast_pgd_range(). This is normally fine, but when the fourth level of page-table is folded at runtime, pud_offset_lockless() will offset from the address of the 'p4d_t' to calculate the address of the PUD in the same page-table page. This results in a stray stack read when the 'p4d_t' has been allocated on the stack and can send the walker into the weeds.
[...]
Applied to arm64 (for-next/core), thanks!
[1/1] arm64: mm: Fix lockless walks with static and dynamic page-table folding https://git.kernel.org/arm64/c/36639013b346
Cheers,