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 6425619DF4F; Mon, 15 Sep 2025 05:48:23 +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=1757915303; cv=none; b=NnQiUxY2wFuIognBsaawOoG2kQ1evvRAqaUwDAYR0xJbKI4ehdO0qwvNwPNkUD22XcyUxB2X0an7G86ttbOnMMSCitqoe+5YULxGJQQuyOaB+FpT2mAcFJTtz5jQ1ucsFx7u1eQRZC8B0aQCt2PT28b1QJO7Ui+pU55BZ8OiwuY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757915303; c=relaxed/simple; bh=QmA1uWtopyZKqYFa3aB5R38vcRhwp6UNA5QEhCCpxlY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=EmIRlyKdzm0hyWCwrNXqF55utMwmqArkWgLr0xxkZi0sRopwMt+PkX42NnEzgPFDoV5Davve/fS9s7/eHt61ICZh6poB2Ph4ckH/Xy8iKC7yLQ2o9sadbtWN41w+PTbNOyzjqaLoo/7XijgSHqmhRdpwsghXHU2tAesJEdv/CEo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LY4R44OP; 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="LY4R44OP" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E1FCDC4CEF1; Mon, 15 Sep 2025 05:48:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1757915302; bh=QmA1uWtopyZKqYFa3aB5R38vcRhwp6UNA5QEhCCpxlY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=LY4R44OPNzL3Qer2vVNQup9uUTcNx43gZqh5FwLU0Oh1PdFVX0Y/KMu9Uvifa32bq LKQg8b7U2pc5ik4+PxHv4Vxaw4OOg+vsmxh8TnpYqhx/pMCEM27S4kfw09R8Z3+SrS WOCH3NphTYB7cis3wXHahmF9XEuFQFnTdwnEgrsxicfvxKQHyvsgH5+RBeSZZNlt+1 jN5OeNDI/I13LeozFgh3Z/w6y7Zqmf8gbZ1coqUma25WZo+AQ3j6hF69NbTonbiUow a8r0c3Mzdr4L7umKhPtyml+GICc0Iz7CXrXjBFFY5PAmWMihDcJf2V0TWoeJPC1g6V RKkFNq598mfYQ== Date: Fri, 12 Sep 2025 12:03:27 +0300 From: Leon Romanovsky To: Marek Szyprowski Cc: Jason Gunthorpe , Abdiel Janulgue , Alexander Potapenko , Alex Gaynor , Andrew Morton , Christoph Hellwig , Danilo Krummrich , David Hildenbrand , iommu@lists.linux.dev, Jason Wang , Jens Axboe , Joerg Roedel , Jonathan Corbet , Juergen Gross , kasan-dev@googlegroups.com, Keith Busch , linux-block@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-nvme@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-trace-kernel@vger.kernel.org, Madhavan Srinivasan , Masami Hiramatsu , Michael Ellerman , "Michael S. Tsirkin" , Miguel Ojeda , Robin Murphy , rust-for-linux@vger.kernel.org, Sagi Grimberg , Stefano Stabellini , Steven Rostedt , virtualization@lists.linux.dev, Will Deacon , xen-devel@lists.xenproject.org Subject: Re: [PATCH v6 00/16] dma-mapping: migrate to physical address-based API Message-ID: <20250912090327.GU341237@unreal> References: <0db9bce5-40df-4cf5-85ab-f032c67d5c71@samsung.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@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: <0db9bce5-40df-4cf5-85ab-f032c67d5c71@samsung.com> On Fri, Sep 12, 2025 at 12:25:38AM +0200, Marek Szyprowski wrote: > On 09.09.2025 15:27, Leon Romanovsky wrote: > > From: Leon Romanovsky > > > > Changelog: > > v6: > > * Based on "dma-debug: don't enforce dma mapping check on noncoherent > > allocations" patch. > > * Removed some unused variables from kmsan conversion. > > * Fixed missed ! in dma check. > > v5: https://lore.kernel.org/all/cover.1756822782.git.leon@kernel.org > > * Added Jason's and Keith's Reviewed-by tags > > * Fixed DMA_ATTR_MMIO check in dma_direct_map_phys > > * Jason's cleanup suggestions > > v4: https://lore.kernel.org/all/cover.1755624249.git.leon@kernel.org/ > > * Fixed kbuild error with mismatch in kmsan function declaration due to > > rebase error. > > v3: https://lore.kernel.org/all/cover.1755193625.git.leon@kernel.org > > * Fixed typo in "cacheable" word > > * Simplified kmsan patch a lot to be simple argument refactoring > > v2: https://lore.kernel.org/all/cover.1755153054.git.leon@kernel.org > > * Used commit messages and cover letter from Jason > > * Moved setting IOMMU_MMIO flag to dma_info_to_prot function > > * Micro-optimized the code > > * Rebased code on v6.17-rc1 > > v1: https://lore.kernel.org/all/cover.1754292567.git.leon@kernel.org > > * Added new DMA_ATTR_MMIO attribute to indicate > > PCI_P2PDMA_MAP_THRU_HOST_BRIDGE path. > > * Rewrote dma_map_* functions to use thus new attribute > > v0: https://lore.kernel.org/all/cover.1750854543.git.leon@kernel.org/ > > ------------------------------------------------------------------------ > > > > This series refactors the DMA mapping to use physical addresses > > as the primary interface instead of page+offset parameters. This > > change aligns the DMA API with the underlying hardware reality where > > DMA operations work with physical addresses, not page structures. > > > > The series maintains export symbol backward compatibility by keeping > > the old page-based API as wrapper functions around the new physical > > address-based implementations. > > > > This series refactors the DMA mapping API to provide a phys_addr_t > > based, and struct-page free, external API that can handle all the > > mapping cases we want in modern systems: > > > > - struct page based cacheable DRAM > > - struct page MEMORY_DEVICE_PCI_P2PDMA PCI peer to peer non-cacheable > > MMIO > > - struct page-less PCI peer to peer non-cacheable MMIO > > - struct page-less "resource" MMIO > > > > Overall this gets much closer to Matthew's long term wish for > > struct-pageless IO to cacheable DRAM. The remaining primary work would > > be in the mm side to allow kmap_local_pfn()/phys_to_virt() to work on > > phys_addr_t without a struct page. > > > > The general design is to remove struct page usage entirely from the > > DMA API inner layers. For flows that need to have a KVA for the > > physical address they can use kmap_local_pfn() or phys_to_virt(). This > > isolates the struct page requirements to MM code only. Long term all > > removals of struct page usage are supporting Matthew's memdesc > > project which seeks to substantially transform how struct page works. > > > > Instead make the DMA API internals work on phys_addr_t. Internally > > there are still dedicated 'page' and 'resource' flows, except they are > > now distinguished by a new DMA_ATTR_MMIO instead of by callchain. Both > > flows use the same phys_addr_t. > > > > When DMA_ATTR_MMIO is specified things work similar to the existing > > 'resource' flow. kmap_local_pfn(), phys_to_virt(), phys_to_page(), > > pfn_valid(), etc are never called on the phys_addr_t. This requires > > rejecting any configuration that would need swiotlb. CPU cache > > flushing is not required, and avoided, as ATTR_MMIO also indicates the > > address have no cacheable mappings. This effectively removes any > > DMA API side requirement to have struct page when DMA_ATTR_MMIO is > > used. > > > > In the !DMA_ATTR_MMIO mode things work similarly to the 'page' flow, > > except on the common path of no cache flush, no swiotlb it never > > touches a struct page. When cache flushing or swiotlb copying > > kmap_local_pfn()/phys_to_virt() are used to get a KVA for CPU > > usage. This was already the case on the unmap side, now the map side > > is symmetric. > > > > Callers are adjusted to set DMA_ATTR_MMIO. Existing 'resource' users > > must set it. The existing struct page based MEMORY_DEVICE_PCI_P2PDMA > > path must also set it. This corrects some existing bugs where iommu > > mappings for P2P MMIO were improperly marked IOMMU_CACHE. > > > > Since ATTR_MMIO is made to work with all the existing DMA map entry > > points, particularly dma_iova_link(), this finally allows a way to use > > the new DMA API to map PCI P2P MMIO without creating struct page. The > > VFIO DMABUF series demonstrates how this works. This is intended to > > replace the incorrect driver use of dma_map_resource() on PCI BAR > > addresses. > > > > This series does the core code and modern flows. A followup series > > will give the same treatment to the legacy dma_ops implementation. > > Applied patches 1-13 into dma-mapping-for-next branch. Let's check if it > works fine in linux-next. Thanks a lot. > > Best regards > -- > Marek Szyprowski, PhD > Samsung R&D Institute Poland > >