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h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=tUnZicFS6DDHwNp7DB2mtYFmNTdq4Tex2cDVTJRe/IxGJoy1g3goY3hNlCLRaWfIc zl3fvjq3Duh1oUMdlU3D1WJbGPFMB1sv7OryckcWhUBYTL22ot8PfWqXCKv+AbDVo4 CBpGXbIjmoScDJVn8NQnl0jwiy7Ex5RIv+iuWHO4= Date: Sun, 7 Jun 2026 21:31:16 +0100 From: Catalin Marinas To: Tejun Heo Cc: bot+bpf-ci@kernel.org, Will Deacon , Alexei Starovoitov , david@kernel.org, arighi@nvidia.com, memxor@gmail.com, akpm@linux-foundation.org, rppt@kernel.org, andrii@kernel.org, daniel@iogearbox.net, martin.lau@linux.dev, martin.lau@kernel.org, eddyz87@gmail.com, yonghong.song@linux.dev, emil@etsalapatis.com, void@manifault.com, changwoo@igalia.com, clm@meta.com, ihor.solodrai@linux.dev, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1780862659.ccb18e27e916dc4b@kernel.org> X-Rspamd-Queue-Id: 97A4E100003 X-Stat-Signature: x3ohbznj84fn3p5wdsow9oa4xex1dfix X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1780864284-627986 X-HE-Meta: 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 Ypv9vjKn LPCEvaiPaJUmeNZhSVCoohdkXcoziCRa7QLaTxzt8Y2A6zBhUJv4CaLCGYNs8wSFR8gvubYchEbVBRRZgnR7Y1SyWKFl9xRzRYuiLeGUQdprWXs+Od3QWbCTc+ukCsK6CE1ggZCrusaEwTZKM40tdl6YhF19jf3j1PoazXhVbszG9bYhE12y4wPnZcenJvGdMi/PyticUV/Wey8O9ih3tdfFTlC7jhKCmbrDTh11qYFCFA/MfwCzm3BSRu1N/eWSOULwZaSBq6Ee3yabzpMNTYpdXX8F19ym92DPuHlFsFoAwz7j5FZ9Xef0JZAqWUIs2+qcEGU8bukIJFMB4XMifpXX40fRhYnyXLWYItkf2XnNNJh2AyO0KFv2KOPgufClubPZRhljt7c8TWAE= 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 10:04:19AM -1000, Tejun Heo wrote: > > Can this path actually loop, or is the deferred barrier guaranteed to be > > flushed before the faulting instruction is retried? > > I don't know the arm64 paths well enough to say. What I can see is that > ptep_try_set() only runs as an apply_to_page_range() callback, and > apply_to_pte_range() brackets it with lazy_mmu_mode_enable()/disable(), with > the disable() flushing TIF_LAZY_MMU_PENDING before returning. The barriers > would land before the access is retried. It also looks like the same > queue_pte_barriers() path __set_pte() already uses. I'd defer to Catalin and > the arm64 folks on whether that actually closes the case. I don't fully understand the BPF parts but I think the bots have a point. If a BPF kprobe fires while we are in lazy mmu mode, __set_pte_complete() will defer issuing the barriers. I think better to just call emit_pte_barriers() directly. If ptep_try_set() is always called with valid kernel ptes, we can skip the if (pte_valid_not_user()) check as well (which was just an optimisation anyway). -- Catalin