From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f53.google.com (mail-wm1-f53.google.com [209.85.128.53]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CE9CB1C84D0 for ; Wed, 31 Dec 2025 14:02:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.53 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767189726; cv=none; b=rwxCa/OZlg1EM1ndsO64lw5s/Rfwy9rlWW/JWJ2bkRFQypl5mQdipwTkQq4RiZzqH/weiijVYixVTa9xaIPsGwfcq+RKpTQhb/Q5BKiLybycJ+tkdzX2SesGNnZzk4mMCV5wi9yHZORHb36krvcRwt0I1sG+PZbiGMrL6DmKNzE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767189726; c=relaxed/simple; bh=4Hf8qGAfIDnMbElA9BV7uSYKEWjXXxN6zt+BgVtPhAs=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=U0zBUtq0TfMSltIlcqCZTDDgCHXpERwD+/pNSMYcRM19CFKYMzPzOQcJc0QulXJGV0y8SO4rG1t8/YDQ0JtBiY7HJrwygQCv7+rMHEM5wq87QmaPnNmiSODXCgUXcNF18tz6DqW4vzCeTjeSXJC/iwTib6V954TQKJ48yfo6y0A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com; spf=pass smtp.mailfrom=suse.com; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b=f+D1ouYW; arc=none smtp.client-ip=209.85.128.53 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b="f+D1ouYW" Received: by mail-wm1-f53.google.com with SMTP id 5b1f17b1804b1-4779d8286d8so7478925e9.0 for ; Wed, 31 Dec 2025 06:02:03 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=google; t=1767189722; x=1767794522; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:from:to:cc:subject:date :message-id:reply-to; bh=kF3B5IdjLDGAw+kMK0g4LlwArvDLn5Kmbe4r9Q45hmQ=; b=f+D1ouYWMJ1UqzYlbVRrds9ZuhaEIzCognWhf5Hu9rZQP8kr2ApNEsiqTRT3GYMeoV sTa9PyUVAVWltZHod9NBZo07NQd+5X9JlqWSrj09UZkyQRmOcSZz7FHyCxDN1cHTuFnp yIsTYnwTIVGyyvBw7kvXeM4S9Nyho1/0zeDYA+gEBae7mjBOy/Dh1XEYjZoCh83ekN0m 1WgXXsYEkystG5HLfaWousHU2nAfPYVcQpyxiZPu8DYAEnVP802z6Uer+QJ1WyElaMky 7vjHK6ou3VoLPXT8CfAA9VJ6V/eJcyxhmOgh9Tf6u1z60ZC3+EaHXb49xMq5eeOIPt6f iDig== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1767189722; x=1767794522; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=kF3B5IdjLDGAw+kMK0g4LlwArvDLn5Kmbe4r9Q45hmQ=; b=u5SLnshjyb4GrE01mhz828e3TO1aL6Vwk3KZKaVET0Ok2SieJhrg/CXM549A6rMj8o Bnknuj/DzOvXU8dX/SbvJU3PWCG962bUTRlE/QdLhrCAaZWolkLqtVH/F/MiivN9iW1C dWAkJobAMNu9gDC4ClXED3d0FZtOBJl5rD+fKJeAvYbaiFYajlwaqywPcrrR15M4oExB ERxhAMmrNq1eBzquMdCZOdH6aGHcR2paaakPEx6InecpX45lUgmz5/k0pLjScyo2TPrB C+J5+apDGLaXZfmaUULX+VO/IpbSklwfoL28XWm9hK/+X7H08FSGb8fccVk6h/RjewtD pqOA== X-Forwarded-Encrypted: i=1; AJvYcCV+HiUSgzphYwk/KoWTFzYoQ53CCt7qFNG3BWX1Dgzz+9EUxpJi0ZB6TJjaenduv937S7A=@vger.kernel.org X-Gm-Message-State: AOJu0YyZxs7kBRav1S8PkG/H6JVXy1rS6hI9KzpVNscK5uxKDIZBbDqG IJKawRp8+tCTNAe8OvcoYqT1UHCO82jt5orW+IxEM360yPoUyEMn8ObTdiCdN0qJskM= X-Gm-Gg: AY/fxX6Sterg7TWtFhUdyEI+4NfqYHptTH2CEC4e4g8G68TXR3vWVAPOEjTePMDFNaN REa1YtnJsaagHWzQYsmCFOssOtDLPkXDL4BNJNQJZmfPTkW19Bwd8fuNmTji4ho8dXnFB8OWDNl +M8qzJgKMtBo/UEVDRPP3DyXMWw0YJnd22jClY7dCMrtJhvB/EhFdkAKRRu243BYoOWLiu5LV34 oC0XNF09opFewLDXEPtOBJrm1m6oYnR1Xcj/qKvgKmTGgNCrq3rdDQ4H+X6K4DlHPdF/wNbDU0X 3JfmDsgANYzX1SFljYz2QkB6Tc9lFzh5KImVdpemJBREjgLCQKoxq+uFvNrrko1irlkcnrPnq4L E5Z+bQy+J2youmBn5SG7S/i3QKKUhPIXOMw6Is5zXyEZ/IWRqx5nm+uhRPVFZKiyBHP2vsyemah +M3bSgF7mEZdY6ovDTU11xFGBCGYRg69mmIW9b6UKsuo09A64AuEa1FOH0WKlzMTCAiMQMgtZYC wmc X-Google-Smtp-Source: AGHT+IE0s0lyU5FbbMJZMjZzb/JdJphgG95YZRZrXFcSa/kp+KRPaXRAnUQjMNNmxS+JnzgO7HwnTw== X-Received: by 2002:a05:600c:4fc6:b0:47a:94fc:d063 with SMTP id 5b1f17b1804b1-47d19538e2cmr221697055e9.1.1767189721959; Wed, 31 Dec 2025 06:02:01 -0800 (PST) Received: from mordecai (dynamic-2a00-1028-83b8-1e7a-3010-3bd6-8521-caf1.ipv6.o2.cz. [2a00:1028:83b8:1e7a:3010:3bd6:8521:caf1]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4324eab2ebfsm73767887f8f.40.2025.12.31.06.02.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 31 Dec 2025 06:02:01 -0800 (PST) Date: Wed, 31 Dec 2025 15:01:59 +0100 From: Petr Tesarik To: "Michael S. Tsirkin" Cc: linux-kernel@vger.kernel.org, Cong Wang , Jonathan Corbet , Olivia Mackall , Herbert Xu , Jason Wang , Paolo Bonzini , Stefan Hajnoczi , Eugenio =?UTF-8?B?UMOpcmV6?= , "James E.J. Bottomley" , "Martin K. Petersen" , Gerd Hoffmann , Xuan Zhuo , Marek Szyprowski , Robin Murphy , Stefano Garzarella , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Leon Romanovsky , Jason Gunthorpe , linux-doc@vger.kernel.org, linux-crypto@vger.kernel.org, virtualization@lists.linux.dev, linux-scsi@vger.kernel.org, iommu@lists.linux.dev, kvm@vger.kernel.org, netdev@vger.kernel.org Subject: Re: [PATCH RFC 01/13] dma-mapping: add __dma_from_device_align_begin/end Message-ID: <20251231150159.1779b585@mordecai> In-Reply-To: References: X-Mailer: Claws Mail 4.3.1 (GTK 3.24.51; x86_64-suse-linux-gnu) Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 30 Dec 2025 05:15:46 -0500 "Michael S. Tsirkin" wrote: > When a structure contains a buffer that DMA writes to alongside fields > that the CPU writes to, cache line sharing between the DMA buffer and > CPU-written fields can cause data corruption on non-cache-coherent > platforms. > > Add __dma_from_device_aligned_begin/__dma_from_device_aligned_end > annotations to ensure proper alignment to prevent this: > > struct my_device { > spinlock_t lock1; > __dma_from_device_aligned_begin char dma_buffer1[16]; > char dma_buffer2[16]; > __dma_from_device_aligned_end spinlock_t lock2; > }; > > When the DMA buffer is the last field in the structure, just > __dma_from_device_aligned_begin is enough - the compiler's struct > padding protects the tail: > > struct my_device { > spinlock_t lock; > struct mutex mlock; > __dma_from_device_aligned_begin char dma_buffer1[16]; > char dma_buffer2[16]; > }; This works, but it's a bit hard to read. Can we reuse the __cacheline_group_{begin, end}() macros from ? Something like this: #define __dma_from_device_group_begin(GROUP) \ __cacheline_group_begin(GROUP) \ ____dma_from_device_aligned #define __dma_from_device_group_end(GROUP) \ __cacheline_group_end(GROUP) \ ____dma_from_device_aligned And used like this (the "rxbuf" group id was chosen arbitrarily): struct my_device { spinlock_t lock1; __dma_from_device_group_begin(rxbuf); char dma_buffer1[16]; char dma_buffer2[16]; __dma_from_device_group_end(rxbuf); spinlock_t lock2; }; Petr T > Signed-off-by: Michael S. Tsirkin > --- > include/linux/dma-mapping.h | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h > index aa36a0d1d9df..47b7de3786a1 100644 > --- a/include/linux/dma-mapping.h > +++ b/include/linux/dma-mapping.h > @@ -703,6 +703,16 @@ static inline int dma_get_cache_alignment(void) > } > #endif > > +#ifdef ARCH_HAS_DMA_MINALIGN > +#define ____dma_from_device_aligned __aligned(ARCH_DMA_MINALIGN) > +#else > +#define ____dma_from_device_aligned > +#endif > +/* Apply to the 1st field of the DMA buffer */ > +#define __dma_from_device_aligned_begin ____dma_from_device_aligned > +/* Apply to the 1st field beyond the DMA buffer */ > +#define __dma_from_device_aligned_end ____dma_from_device_aligned > + > static inline void *dmam_alloc_coherent(struct device *dev, size_t size, > dma_addr_t *dma_handle, gfp_t gfp) > {