From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 34A25303A1B; Wed, 26 Nov 2025 15:13:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764169986; cv=none; b=bIZ2Y3WCU+wA01URNIPpYuklflzwqbLj+p57ea6jv1AtnhzzRPsovHH+L3S9wv20Vbqk4x5pMoOrXREAKWVqbrS7iOLr54H4wSdWybQ8tenJ4NAPqEa97WLf8GGy4ducuKoKrjHz3n0YJWLHYvoaoEF2yldZHlD3re1CR10omaU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764169986; c=relaxed/simple; bh=0u1o2KJFgGMlu+9bXPvNMO4fZcJG4zl5WGYFbdjOE0Y=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ge2PLjDeBkTMz0uj6yU2CF1IFYsYSqjv5kJ/MuJPa8mztdau/cNbTGeCxsYpV19oAFA0HC47GX1cTVccO4uC98UyRj0YUf01yLre4EPr/xc/bUe1zycYCGVm8lY9aElfl/3jqz9YxrSIERUAy2N0OY6bbrzwF9LlqXvAdeDuPYY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=XvQkRN19; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="XvQkRN19" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7514BC4CEF8; Wed, 26 Nov 2025 15:13:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1764169986; bh=0u1o2KJFgGMlu+9bXPvNMO4fZcJG4zl5WGYFbdjOE0Y=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=XvQkRN19LTR69pvq2REcXFW4oZY2i6UXRWgCyQ+XMFsOHihwUBtRRoLFAqpzZh/7A QSmA9b7gJXSongNcKgQRd0Tl81WGpeWnFPHPCE5XLU20g83tc9/LiFpPnla6RobhWK 7WJlJ68CBeBqZnbfDcilHelOkUJ0XgBa6yhQJsUpyY/AdVSi5b3JtEZV6jjvvo9rro X6orAvcL9QSKPyIUJnbAqHNObN42cyYmzMr89w7Nu4SWB423xBfhJFOM6bKgasGFaD N7TmXBm8NiGtSi1DuX0uaQ4PdUWXN3llZdwJ/rL/iuND4nZeCj68zfriwWrVUeIyRT Yu5/d68RRECEg== Message-ID: Date: Wed, 26 Nov 2025 16:12:59 +0100 Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 06/22] mm: Always use page table accessor functions To: Lorenzo Stoakes Cc: Ryan Roberts , Wei Yang , Samuel Holland , Palmer Dabbelt , Paul Walmsley , linux-riscv@lists.infradead.org, Andrew Morton , linux-mm@kvack.org, devicetree@vger.kernel.org, Suren Baghdasaryan , linux-kernel@vger.kernel.org, Mike Rapoport , Michal Hocko , Conor Dooley , Krzysztof Kozlowski , Alexandre Ghiti , Emil Renner Berthing , Rob Herring , Vlastimil Babka , "Liam R . Howlett" , Julia Lawall , Nicolas Palix , Anshuman Khandual References: <6bdf2b89-7768-4b90-b5e7-ff174196ea7b@lucifer.local> <71123d7a-641b-41df-b959-88e6c2a3a441@kernel.org> <20251126134726.yrya5xxayfcde3kl@master> <6b966403-91e0-4f06-86a9-a4f7780b9557@kernel.org> <1ca9f99f-6266-47ca-8c94-1a9b9aaa717f@kernel.org> <37973e21-e8f4-4603-b93d-4e0b1b2499fa@lucifer.local> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: <37973e21-e8f4-4603-b93d-4e0b1b2499fa@lucifer.local> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11/26/25 16:08, Lorenzo Stoakes wrote: > On Wed, Nov 26, 2025 at 03:56:13PM +0100, David Hildenbrand (Red Hat) wrote: >> On 11/26/25 15:52, Lorenzo Stoakes wrote: >>> >>> Would the pmdp_get() never get invoked then? Or otherwise wouldn't that end up >>> requiring a READ_ONCE() further up the stack? >> >> See my other reply, I think the pmdp_get() is required because all pud_* >> functions are just simple stubs. > > OK, thought you were saying we should push further down the stack? Or up > depending on how you view these things :P as in READ_ONCE at leaf? I think at leaf because I think the previous ones should essentially be only used by stubs. But I haven't fully digested how this is all working. Or supposed to work. I'm trying to chew through the arch/arm/include/asm/pgtable-2level.h example to see if I can make sense of it, > > Anyway. I am now designating you the expert at this ;) Oh no. :) > >> >>> >>>> >>>> IOW, push the READ_ONCE() down to the lowest level so the previous ones >>>> (that will get essentially ignore?) will get folded into the last >>>> READ_ONCE()? >>>> >>>> But my head still hurts and I am focusing on something else concurrently :) >>> >>> Even if we could make this work, I don't love that there's some implicit >>> assumption there that could easily break later on. >>> >>> I'd rather we kept it as stupid/obvious as possible... >> >> Looking at include/asm-generic/pgtable-nopmd.h I am not sure we are talking >> about implicit assumptions here. It's kind-of the design that the pud_t >> values are dummies, so why shoul the pudp_get() give you any guarantees. >> >> At least that's my current understanding, which might be very flawed :) > > I mean I'm waving my hands around like I'm working on an aircraft carrier here > so if you're _sure_ it's _absolutely_ safe then fine :) Well, not yet ... :) -- Cheers David