Re: [PATCH v2 bpf-next] arm64: mm: Complete the PTE store in ptep_try_set()
From: Catalin Marinas <catalin.marinas@arm.com>
Date: 2026-06-08 08:43:36
Also in:
bpf, linux-mm, lkml
On Sun, Jun 07, 2026 at 09:25:47PM -1000, Tejun Heo wrote:
ptep_try_set() installs a kernel PTE with try_cmpxchg() but, unlike __set_pte(), skips the barriers that arm64 requires after writing a valid kernel PTE. Without them a subsequent access can fault instead of seeing the new mapping. Issue them with emit_pte_barriers() rather than __set_pte_complete(). ptep_try_set() must finish the store before it returns, but __set_pte_complete() would defer the barriers when the calling context is in lazy MMU mode. v2: Emit the barriers directly instead of __set_pte_complete(). (Catalin)
Nit: I'd place this after the --- line.
quoted hunk ↗ jump to hunk
Fixes: 258df8fce42f ("mm: Add ptep_try_set() for lockless empty-slot installs") Suggested-by: Catalin Marinas <catalin.marinas@arm.com> Link: https://lore.kernel.org/all/aiRFcz78QTZdIHHB@arm.com/ (local) Signed-off-by: Tejun Heo <tj@kernel.org> --- arch/arm64/include/asm/pgtable.h | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index 3ce0f2a6cab6..3e579c26b383 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h@@ -1838,7 +1838,16 @@ static inline bool ptep_try_set(pte_t *ptep, pte_t new_pte) { pteval_t old = 0; - return try_cmpxchg(&pte_val(*ptep), &old, pte_val(new_pte)); + if (!try_cmpxchg(&pte_val(*ptep), &old, pte_val(new_pte))) + return false; + + /* + * The store must be complete by the time this returns, but the caller + * may be in lazy MMU mode, where __set_pte_complete() would defer the + * barriers. Issue them directly. + */ + emit_pte_barriers(); + return true; } #define ptep_try_set ptep_try_set
It looks fine now. Thanks! Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>