From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 9A2413CDBC3; Wed, 8 Jul 2026 06:36:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783492610; cv=none; b=f3++WZjYaeaznCF/wAr7tik7PgDWOrpCSHzz6FtPygZIVmFzDv6VQPLYeO1qgVohb34ErM7GC5yL8uzfLu4M/AYJ9IkVd4DxVGm0+GXBnRY0jjNNNAv2D9xptKk8grsmh2KMoOVOKNzOPmqjIHuxNTbIcGRmM08JC4/QkyU3dLg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783492610; c=relaxed/simple; bh=0VAulgCnbgot4cpP8JKj1m59gLCXA5naUEjVGiur4yU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=bdq4t8ctTKvPPK8EDrrrPfXhu4vIcvFvEgwleYkwY4COhcOyZ6PbPF6OghrdvZIYI7qKxS1wIUV+o9nRcveLpO7UGlfjdirMtPzrDJxeg9ovvwm84UoqyvdlMb4LEP6C4twIQePf8zCp99V/PahJbIutvBMOgXjnVI9f+Z55n0M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=TxzNfxkA; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="TxzNfxkA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1EE831F000E9; Wed, 8 Jul 2026 06:36:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783492605; bh=s0HJkQVRyCuHBvyWHHR+93fIn2+uXye8kCTNUU3r60I=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=TxzNfxkAbGy4rqJIqCr89/xbSHEkX+rin+tyCSt7590zWJuMCw8dcQKrSCNVIiWoA ndOV/GgWovh0WUxdtvgi0EtOpL/TilvEb2DV/Haj7x+l+Y6wUpasj2HUpo6QNlgM2K FXdGWdWH5cn/DW+KWFvNGyKQiWhHS8hgb6rAvdnbskLQw7CGy/oixnnHzdKAsVfU8i Ckw1IGQsAI4HAECNOWyM3Pg5nt+m9bUKguiwdqud8b7wpl/lsMWQrtFW3E8+u/b4Vo qizUfCiYMop6IHGz5Ym885tLg6yCjh+X38Gv1RHOK0ly9wgNDvXOadV5LseTU5F1jP 7eax4QVB5vPgw== Date: Wed, 8 Jul 2026 09:36:25 +0300 From: Mike Rapoport To: Will Deacon Cc: Thierry Reding , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Jonathan Hunter , David Airlie , Simona Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Sowjanya Komatineni , Luca Ceresoli , Mikko Perttunen , Yury Norov , Rasmus Villemoes , Russell King , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Sven Schnelle , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Marek Szyprowski , Robin Murphy , Sumit Semwal , Benjamin Gaignard , Brian Starkey , John Stultz , "T.J. Mercier" , Christian =?iso-8859-1?Q?K=F6nig?= , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Catalin Marinas , Thierry Reding , devicetree@vger.kernel.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-s390@vger.kernel.org, linux-mm@kvack.org, iommu@lists.linux.dev, linaro-mm-sig@lists.linaro.org, linux-trace-kernel@vger.kernel.org, Thierry Reding , Chun Ng , Shyam Saini Subject: Reserving memory on ACPI systems (was: [PATCH v3 04/11] arm64/mm: Add set_memory_device() and set_memory_normal()) Message-ID: References: <20260701-tegra-vpr-v3-0-d80f7b871bb4@nvidia.com> <20260701-tegra-vpr-v3-4-d80f7b871bb4@nvidia.com> Precedence: bulk X-Mailing-List: linux-tegra@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri, Jul 03, 2026 at 06:13:31PM +0100, Will Deacon wrote: > On Thu, Jul 02, 2026 at 06:41:23PM +0200, Thierry Reding wrote: > > On Thu, Jul 02, 2026 at 03:46:44PM +0200, Thierry Reding wrote: > > > On Thu, Jul 02, 2026 at 10:18:47AM +0100, Will Deacon wrote: > > > > On Wed, Jul 01, 2026 at 06:08:15PM +0200, Thierry Reding wrote: > > > > > From: Chun Ng > > > > > > > > > > Add helpers to swap PROT_NORMAL and PROT_DEVICE_nGnRnE protection bits > > > > > on a kernel-linear-map range. > > > > > > > > That sounds like a really terrible idea. Why is this necessary and how > > > > does it interact with things like load_unaligned_zeropad()? > > > > > > This is necessary because once the memory controller has walled off the > > > new memory region the CPU must not access it under any circumstances or > > > it'll cause the CPU to lock up (I think technically it'll hit an SError > > > but in practice that just means it'll freeze, as far as I can tell). > > > > > > Probably doesn't interact well at all with load_unaligned_zeropad(). > > > > > > > I think you should unmap the memory from the linear map and memremap() > > > > it instead. > > > > > > Given that the memory can never be accessed by the CPU after the memory > > > controller locks it down, I don't think we'll even need memremap(). The > > > only thing we really need is the sg_table we hand out via the DMA BUFs > > > so that they can be used by device drivers to program their DMA engines > > > internally. > > > > > > Looking through some of the architecture code around this, shouldn't we > > > simply be using set_memory_encrypted() and set_memory_decrypted() for > > > this? While they might've been created for slightly other use-cases, > > > they seem to be doing exactly what we want (i.e. remove the page range > > > from the linear mapping and flushing it, or restoring the valid bit and > > > standard permissions, respectively). > > > > Ah... I guess we can't do it because we're not in a realm world and so > > the early checks in __set_memory_enc_dec() would return early and turn > > it into a no-op. > > > > How about if I extract a common helper and provide set_memory_p() and > > set_memory_np() in terms of those. Those are available on x86 and > > PowerPC as well, so fairly standard. I suppose at that point we're > > closer to set_memory_valid(). > > Why not just call set_direct_map_invalid_noflush() + > flush_tlb_kernel_range() for each page? We already have APIs for this. > > The big challenge I see with any linear map manipulation, however, is > that it will rely on can_set_direct_map() which likely means you need to > give up some performance and/or security to make this work. Does memory > become inaccesible dynamically at runtime? If not, the best bet would > be to describe it as a carveout in the DT and mark it as "no-map" so > we avoid mapping it in the first place. While I got your attention a bit off-topic but still related question. AFAIK a lot in arm64 drivers ecosystem relies on that ranges defined as "/reserved-memory" in DT are linked to devices that use that memory. EFI/ACPI does not have a similar concept. Given that more and more systems are using EFI/ACPI rather than DT as their boot protocol we probably need some way to define such memory carveouts in the ACPI world. > Will -- Sincerely yours, Mike.