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Thu, 1 Oct 2026 12:34:16 +0000 (UTC) Authentication-Results: lists.trustedfirmware.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=if4SvAJ1; dkim-atps=neutral Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id E3DEA401C2; Thu, 1 Oct 2026 12:34:15 +0000 (UTC) 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 To: Will Deacon 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> MIME-Version: 1.0 Content-Type: text/plain; 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no-senders; approved; emergency; loop; banned-address; member-moderation; header-match-op-tee.lists.trustedfirmware.org-0; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header 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 X-Mailman-Version: 3.3.5 Precedence: list List-Id: Archived-At: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: From: Sumit Garg via OP-TEE Reply-To: Sumit Garg 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