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 315D93DA7C4; Thu, 1 Oct 2026 12:34:15 +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=1790858057; cv=none; b=XNq6vzEPvYx6VU6Ci+iHMrxyFRvDAdS07O64qOJ588lNiI2WFxlxwg/v8Gbx0LHsCn+apqyjzxbEzjt4QeyLqesOdtZHohN/wjihjEJdbqQp20i92ksuvbgnsVxpX2fmEFta+5H+Dks3kln/3MbshC7P36nIYi1t+pHZ/f3zHLU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790858057; c=relaxed/simple; bh=QVF2nURRP7xz9O0Kq+Vq/PtyCz1+E71O3hLTPrAnM60=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=VL25YSOu6ka2aZgbOvQFtnD0l9/Kj5eKgNouBC6VJMheaImyjwr79M1o14WdNLGca1PQSWWpE6F/RkYBESxGVURe045rEoKsbU7ftB8Rc4DJqTE9KwQkygaQJ5ClpUT2++WWnb2zIiuT50YhhEA3dGshG+7l4h5SYtw3u4j+V+Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=if4SvAJ1; 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="if4SvAJ1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 47FD81F00898; Thu, 1 Oct 2026 12:34:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790858055; bh=PzSvFLGXXhDhvscc/9MFlHIrUkWd1NO5NFV4BtnVy4A=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=if4SvAJ18eHheJNDIHcxsy7TV/obUhX+e28ofec1ugv6Qzf1xWPauEKNX2d5q4tTp lqIuMR+qdhIvYgLNPo+Xu71RRG2jvwkgCBw9d0spl9LBDZYsQtwcfML4ZVgiSM96eu NziDpTlnYQuD6PZdYxCPJL8kHi9knoo5gRcjO9s2i9wA9xfxVdbp6Yvnr/0AAd0qde D8UclBqsHY5y39KB5plqsT63o4jWH8xj6VEW4Hu89PvcGeID+lsA7y6rvKVYZ9Xbb6 3yejC5BjkVY3QrY5fE+q8ahCPjh/bI+RcEG2FarJLbEFB9YnZ35RB5mMH9dP/3yAwJ NiIHnfgpTOdfw== Date: Thu, 1 Oct 2026 18:04:06 +0530 From: Sumit Garg To: Will Deacon Cc: brendan.jackman@linux.dev, Vincent Donnefort , catalin.marinas@arm.com, rppt@kernel.org, akpm@linux-foundation.org, sudeep.holla@kernel.org, jenswi@kernel.org, robh@kernel.org, mark.rutland@arm.com, ardb@kernel.org, thierry.reding@kernel.org, david@kernel.org, danielmentz@google.com, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, op-tee@lists.trustedfirmware.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 0/8] arm64: Unmap FF-A lent memory from direct map Message-ID: Mail-Followup-To: Will Deacon , brendan.jackman@linux.dev, Vincent Donnefort , catalin.marinas@arm.com, rppt@kernel.org, akpm@linux-foundation.org, sudeep.holla@kernel.org, jenswi@kernel.org, robh@kernel.org, mark.rutland@arm.com, ardb@kernel.org, thierry.reding@kernel.org, david@kernel.org, danielmentz@google.com, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, op-tee@lists.trustedfirmware.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260921110050.3977591-1-vdonnefort@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: On Tue, 29 Sep 2026 at 12:33:07 +0100, Will Deacon wrote: >On Sat, Sep 26, 2026 at 05:43:08PM +0530, Sumit Garg wrote: >> Looks like you dropped me from your reply. > >Huh, that's weird. If I hit reply-all ('g') in mutt, it moves the entire >CC list to To: and drops you. I suspect the same thing happened to Thierry >when he replied here: > >https://lore.kernel.org/all/arJcN60nagFKXj2Q@orome/ > >I can't figure out why that's happening :/ >I manually tried to fix the To: and Cc: lines in this message. Thanks. > >> On Tue, 22 Sep 2026 at 15:55:59 +0100, Will Deacon wrote: >> > I spoke to Brendan at LPC (?) last year but this doesn't really work >> > for arm64 because it relies on being able to unmap arbitrary parts of >> > the linear map, which isn't generally possible unless you force pte-level >> > mappings for everything, which is prohibitive for perf/power. >> >> As per the cover letter it's about allocating pages that are not present >> in the direct map. This essentially fits the protected DMABufs use-case >> where we don't want any kernel mapping to exist at any time. Bufers >> allocated from protected DMABufs are only meant to be accessed by the >> TEE implementation or HW accelerators like in the secure media pipeline. > >That sounds like it should probably build on top of this series, then. The main problem I see with this series is it tries to move from the generic CMA allocator to a reserved FF-A CMA pool which again comes from the DT. We already support reserved pool allocations via "no-map" which are discovered dynamically from OP-TEE. If we can rather support a generic CMA like allocator for arm64 which can support unmapped allocations then I am all for it. These platform specific reserved pools isn't a scalable solution. >You could allocate the DMABufs from a CMA region that has no linear alias. Allocation from generic CMA pool is already the case here: tee_shm_alloc_dma_mem() -> dma_alloc_pages() Do you mean it's just fine to unmap buffers allocated from generic CMA region since it doesn't have any linear alias? > >> > Vincent's series tackles that by using a pool so that only that part of >> > memory requires the pte-level mappings in the linear map. That's the >> > whole point of it, so I don't think it makes sense to drop it in favour >> > of Brendan's approach (which doesn't work). >> > >> >> For protected DMABufs, we even don't require any pte-level mappings in >> linear map. The whole idea of mapping and unmapping is just a bottleneck >> for performance sensitive secure media pipeline use-cases. That's why if >> we can support __GFP_UNMAPPED with the memory allocator on arm64 would >> be the best fit for this use-case. > >The point is that you will require pte-level mappings for the linear map >if you want to unmap from it at runtime on arm64. If you don't, then you >can end up needing to split a block mapping (e.g. pmd-level) when you >decide to unmap only part of it and there isn't a safe way to do that on >arm64 without transiently unmapping the entire block, which can lead to >fatal translation faults during that window. I agree with you here, what I am rather trying to find if on arm64 there is any possibilty to have a generic allocator for unmapped pages. That's the use-case here as well as what Brendan't patch-set was trying to address. > >> Now the question is why arm64 can't support __GFP_UNMAPPED similar to >> how Brendan is doing it for x86? > >Because arm64 != x86? Presumably x86 doesn't have the strict >break-before-make requirements we have on arm64. > Sure, sounds like you are eluding to that the generic MM flag __GFP_UNMAPPED being proposed can't be supported on arm64, right? -Sumit