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b=QmH38l1eV9DBt1+KQ53uym1LwwTyqmzwyRg5m0pDoIA+Xrz+rbRz0g8YFzsm4MF9N XbwOJQCf3U6kkC/HsagR/7Att8ry12jX99u5FxJnmKyyg2De3Tkck93okliih2fgwn dKfqhPMmplROMRTaYG1e0dC3PJcsdvVN9k9lNzvX9ISOhZhmTY+v8muLWGx+uiKw3v 8Fu6FPeoeWRFW3U0dU1ioLThmk/JDD84XAngLZKerCOHjEkki9HAtJ8MKRz7tbIHYL dB33D1+wT1lCYN3KK/vZLGZ+PXSESGjx3A6aSNlzctXGWmYxWqvkA7E7FhHnJVDzel vdHcVqx3qBODQ== Date: Mon, 12 Oct 2026 18:46:12 +0530 From: Sumit Garg To: Vincent Donnefort Cc: Will Deacon , brendan.jackman@linux.dev, 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, sumit.garg@kernel.org Subject: Re: [PATCH v2 0/8] arm64: Unmap FF-A lent memory from direct map Message-ID: References: <20260921110050.3977591-1-vdonnefort@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: E4F3A80007 X-Rspam-User: X-Stat-Signature: aycjb3mdd1dffrtw6yeqzecpce3wrcqd X-HE-Tag: 1791810982-907238 X-HE-Meta: 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 InPvdkXi 17W42CvYkmVQgpYYjSvtALVxHAkLRXZ7ihVqhwWZNEENAeUT210biZUFUXsGd3NIEYKfWHsB7Df3ZuaN1P/ZUxPrgRGaMBJVyxrtx4/vwMrsy+ImzUisxXct2LdsEEAqPD4v6DB972COMl0Dz5mSuKmXvqvDYLA0mTqKmu/bRgNpsOaWWg5KQSmrCYrHY9AN6aXX+q+pxH1ntAWMdqUFvQajPEeypprbW0e+EYgszBj0j4WjIZMcULrB1ts6kGSzaLeKYgY6GzqHeHwnosZNw+/gOKg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 05 Oct 2026 at 12:02:55 +0100, Vincent Donnefort wrote: >Sorry, not sure why Sumit's email was dropped... The problem was with my mutt config, it should be fixed now. > >On Mon, Oct 05, 2026 at 11:48:00AM +0100, Vincent Donnefort wrote: >> On Thu, Oct 01, 2026 at 06:04:06PM +0530, Sumit Garg wrote: >> > 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. >> >> I can't think of a way around a DT declaration. We need to know what region is >> PTE-level before the direct map is installed and of_reserved_mem is very handy >> for that purpose. And as this PTE-level mapping is costly we certainly only want >> to enable it for platforms that absolutely need it. >> I am rather thinking of a way to turn the default CMA allocator to be PTE-level mapped. Since the overall idea for this dynamic protected buffers was to reuse memory efficiently, otherwise the reserved buffer approach is already there to use as "no-map" via DT. If we can have "cma_unmap" cmdline option alongside "cma" then it can turn the existing default CMA allocator to support unmapping buffers. Not requiring a DT change at all, although we can have the DT property for the default pool too if platforms want to opt for. >> > >> > 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. >> >> What do you mean by generic CMA allocator here? An extension to >> shared-dma-pool? Or having the CMA automatically doing the unmap/map on >> cma_alloc() cma_release()? >> >> Right now I have created an API for the unmapping/remapping part. It adds a >> burden on the caller, but the alternative solution is introducing post-alloc >> pre-dealloc callbacks in the CMA, which looked a bit overkilled to me when >> the users of that "ffa-pool" are only optee and the nvidia video dma-buf heap. >> I am not too worried about where the actual implementation lives but looks like CMA driver to be the better place. I think use-cases like guest_memfd proposed as a user for __GFP_UNMAPPED on arm64 will also be looking for this feature. -Sumit >> >> > >> > > 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 > >-- >Vincent From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.trustedfirmware.org (lists.trustedfirmware.org [18.214.241.189]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2B6AFCA9EC5 for ; Mon, 12 Oct 2026 13:16:41 +0000 (UTC) Received: from lists.trustedfirmware.org (localhost [127.0.0.1]) by lists.trustedfirmware.org (Postfix) with ESMTP id 3D4014519E for ; Mon, 12 Oct 2026 13:16:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=lists.trustedfirmware.org; s=2024; t=1791811001; 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Mon, 12 Oct 2026 13:16:21 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 02B841F0089B; Mon, 12 Oct 2026 13:16:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791810981; bh=C6MtMH1ZS7/LqdONAPmFEgAIkbcber8e91yV+8NWqx4=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=QmH38l1eV9DBt1+KQ53uym1LwwTyqmzwyRg5m0pDoIA+Xrz+rbRz0g8YFzsm4MF9N XbwOJQCf3U6kkC/HsagR/7Att8ry12jX99u5FxJnmKyyg2De3Tkck93okliih2fgwn dKfqhPMmplROMRTaYG1e0dC3PJcsdvVN9k9lNzvX9ISOhZhmTY+v8muLWGx+uiKw3v 8Fu6FPeoeWRFW3U0dU1ioLThmk/JDD84XAngLZKerCOHjEkki9HAtJ8MKRz7tbIHYL dB33D1+wT1lCYN3KK/vZLGZ+PXSESGjx3A6aSNlzctXGWmYxWqvkA7E7FhHnJVDzel vdHcVqx3qBODQ== Date: Mon, 12 Oct 2026 18:46:12 +0530 To: Vincent Donnefort Subject: Re: [PATCH v2 0/8] arm64: Unmap FF-A lent memory from direct map Message-ID: References: <20260921110050.3977591-1-vdonnefort@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: X-Rspamd-Action: no action X-Spamd-Result: default: False [-8.50 / 15.00]; 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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: Will Deacon , brendan.jackman@linux.dev, 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, sumit.garg@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 Mon, 05 Oct 2026 at 12:02:55 +0100, Vincent Donnefort wrote: >Sorry, not sure why Sumit's email was dropped... The problem was with my mutt config, it should be fixed now. > >On Mon, Oct 05, 2026 at 11:48:00AM +0100, Vincent Donnefort wrote: >> On Thu, Oct 01, 2026 at 06:04:06PM +0530, Sumit Garg wrote: >> > 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. >> >> I can't think of a way around a DT declaration. We need to know what region is >> PTE-level before the direct map is installed and of_reserved_mem is very handy >> for that purpose. And as this PTE-level mapping is costly we certainly only want >> to enable it for platforms that absolutely need it. >> I am rather thinking of a way to turn the default CMA allocator to be PTE-level mapped. Since the overall idea for this dynamic protected buffers was to reuse memory efficiently, otherwise the reserved buffer approach is already there to use as "no-map" via DT. If we can have "cma_unmap" cmdline option alongside "cma" then it can turn the existing default CMA allocator to support unmapping buffers. Not requiring a DT change at all, although we can have the DT property for the default pool too if platforms want to opt for. >> > >> > 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. >> >> What do you mean by generic CMA allocator here? An extension to >> shared-dma-pool? Or having the CMA automatically doing the unmap/map on >> cma_alloc() cma_release()? >> >> Right now I have created an API for the unmapping/remapping part. It adds a >> burden on the caller, but the alternative solution is introducing post-alloc >> pre-dealloc callbacks in the CMA, which looked a bit overkilled to me when >> the users of that "ffa-pool" are only optee and the nvidia video dma-buf heap. >> I am not too worried about where the actual implementation lives but looks like CMA driver to be the better place. I think use-cases like guest_memfd proposed as a user for __GFP_UNMAPPED on arm64 will also be looking for this feature. -Sumit >> >> > >> > > 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 > >-- >Vincent