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bh=FjzT5RcBQdDdIEoaNoG32miDcUBIMi1hQyHWzkZszv4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Y3K2BCo0/UBNqU0k0thuEuhnek8OYAJF79Xh+dFBb16uvJzUHv0//2JXHjFGytIIY ZTcaOYXijTpBDiXvaHTdKouF7fWJCVNNJxmbHGVH4xqTlTynktxZc/o7XT6d1vqF9l 2bj0jXSxM/9AaXUe8OGPBioPd65MM7iMjNx4qrig= Date: Mon, 8 Jun 2026 09:43:29 +0100 From: Catalin Marinas To: Tejun Heo Cc: Will Deacon , Alexei Starovoitov , David Hildenbrand , Andrea Righi , Kumar Kartikeya Dwivedi , Andrew Morton , Mike Rapoport , Andrii Nakryiko , Daniel Borkmann , Martin KaFai Lau , Eduard Zingerman , Yonghong Song , Emil Tsalapatis , David Vernet , Changwoo Min , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 bpf-next] arm64: mm: Complete the PTE store in ptep_try_set() Message-ID: References: <088f52fd25860ca961449d53f91b214a@kernel.org> <5f68f44310d4878185fd5ebc52d66530b99f174c6d04ab1170dc53cefaa54568@mail.kernel.org> <1780862659.ccb18e27e916dc4b@kernel.org> <7f5f7c94601312c1a401fb18998291cc@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7f5f7c94601312c1a401fb18998291cc@kernel.org> X-Rspamd-Queue-Id: 9E1F61A0006 X-Rspam-User: X-Stat-Signature: 1pn8yzb8ukr57zsd3x9zdraxinifxh5u X-Rspamd-Server: rspam08 X-HE-Tag: 1780908216-307539 X-HE-Meta: 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 tJjsXACD JHoRhPvxU2WhWyxhQ0Kh06E9+ViNYM5L/xhHmSjglR11/Pc6Uu5+qgQZ/x8A3Zau5l5cJBALmFvjgoTXZ/0VJm1mpzCpZtkPaWtahVZ1UN51Uh551t2yPO112qDaQf2I2IEgP1RUmkVITmf5BeASiJ71yMIT8Quuu/UEq9CjOgLnfB+f7dTowmw//jHyEUcTgHu2eFEODE+cfr+DiUDc+pARf5CYTtE9lqEb4SXcuRyJWhual43C+PSoWCwbSkbRhSo++hHgTLy2+DUvCfvRDT/h1816GnDMTRHPtdjo+KPjH78jfG6KWt/x+/Kr1zkuTUFxA+JuWWIHpum34EtWOfarQzmQPxzES8jhH8oWg1qHtZC4= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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. > Fixes: 258df8fce42f ("mm: Add ptep_try_set() for lockless empty-slot installs") > Suggested-by: Catalin Marinas > Link: https://lore.kernel.org/all/aiRFcz78QTZdIHHB@arm.com/ > Signed-off-by: Tejun Heo > --- > 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