From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 E528B189520; Wed, 2 Apr 2025 16:16:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743610594; cv=none; b=sfLPyCddEKaVb5SWDxuHx2p7609HIRIi9IWU6gzKUfAEd2YAqiZD82sr12VfUCJzvPoL2IrZVesgWLs6O3ggbxQEZ79EzaS2VhZ2oYNFIRAMlFGdTfadCo3J0lSAwvv/bqCGeyowgaMHj908CDm43FJJ/sBGq3G3S+IMdLVt0MM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743610594; c=relaxed/simple; bh=U2Hzpo8Um5S3zKUGuOmAn/wJu4MonmSJ2/IHPfGPko0=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=VorlXUGrcw3FSTADvYQeFmtDx7dX6epJAFZw+c/ce8A3j8M6WqaF4Fk86S6O5ktsmIxW4bqUMNuMmyh/XLe0r0i+dOz9A6jbRNzNscZMmHZrpgtK5sUYAUuI2Df1LX55zXBwOXrpJnzdJldHBUkAwBEA5fasjYPpBPnhmFbqkMI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=desiato.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=GYZaqSYA; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=desiato.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="GYZaqSYA" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=Mf3hTtZy2NTjqf//FKiq4P87bc7G1fmFjOKVHZrZIX0=; b=GYZaqSYAj5B/TxQKEqRl8awKsj Psf5RoZh/REQliwHuvdoXOpMXeQMwzOIK0fiQmvBjXTwuUjaOeXffnMwezFU+UZ3j0MrvclTBIyKt ecSxIePgFEbnKNG/FId2yepZ/bhflzPE4PD6hw0N8XpXNkw+10fp2aCmBI0bawtdsbeCrpidP3uCm Hw2l9tszYw2afTqmw4BNT92gJQNw5tpTyI9nJhqDM26HCyUj/cHTF550K1PTjdqo8flEOv8BWopS/ /rNYr7pzL+PPwAys4YUqur2dxfqk/Kzfbmdv5HpQPb2xN9nySQyhMLt4uoX4/T3m/R+vUFWa9JeNn h1lNTR8A==; Received: from [172.31.31.145] (helo=u09cd745991455d.ant.amazon.com) by desiato.infradead.org with esmtpsa (Exim 4.98.1 #2 (Red Hat Linux)) id 1u00lR-0000000741I-0PnI; Wed, 02 Apr 2025 16:16:29 +0000 Message-ID: <965ccf2f972c5d5f1f4edacb227f03171f20e887.camel@infradead.org> Subject: Re: [RFC PATCH 1/3] content: Add VIRTIO_F_SWIOTLB to negotiate use of SWIOTLB bounce buffers From: David Woodhouse To: "Michael S. Tsirkin" Cc: virtio-comment@lists.linux.dev, hch@infradead.org, Claire Chang , linux-devicetree , Rob Herring , =?ISO-8859-1?Q?J=F6rg?= Roedel , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, graf@amazon.de Date: Wed, 02 Apr 2025 17:16:28 +0100 In-Reply-To: <20250402114757-mutt-send-email-mst@kernel.org> References: <20250402112410.2086892-1-dwmw2@infradead.org> <20250402112410.2086892-2-dwmw2@infradead.org> <20250402105137-mutt-send-email-mst@kernel.org> <19ba662feeb93157bc8a03fb0b11cb5f2eca5e40.camel@infradead.org> <20250402111901-mutt-send-email-mst@kernel.org> <6b3b047f1650d91abe5e523dd7f862c6f7ee6611.camel@infradead.org> <20250402114757-mutt-send-email-mst@kernel.org> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-/Bk7qmrjsu2LiljWhG+f" User-Agent: Evolution 3.52.3-0ubuntu1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by desiato.infradead.org. See http://www.infradead.org/rpr.html --=-/Bk7qmrjsu2LiljWhG+f Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2025-04-02 at 11:51 -0400, Michael S. Tsirkin wrote: > On Wed, Apr 02, 2025 at 04:47:18PM +0100, David Woodhouse wrote: > > On Wed, 2025-04-02 at 11:20 -0400, Michael S. Tsirkin wrote: > > > On Wed, Apr 02, 2025 at 04:12:39PM +0100, David Woodhouse wrote: > > > > On Wed, 2025-04-02 at 10:54 -0400, Michael S. Tsirkin wrote: > > > > > > +=C2=A0 If a the device transport provides a software IOTLB bou= nce buffer, > > > > > > +=C2=A0 addresses within its range are not subject to the requi= rements of > > > > > > +=C2=A0 VIRTIO_F_ACCESS_PLATFORM as they are considered to be `= `on-device'' ... > The text you wrote makes it seem that even if the platform says use > an IOMMU, it should be bypassed. It was trying just to state the obvious, that addresses within the range of the *on-device* memory buffer are not handled by the IOMMU. > I would drop this text, and maybe add some clarification in the mmio tran= sport, > as needed. It would be PCI too. I guess we could move the "obvious" comment that 'addresses within the range of the SWIOTLB bounce buffer region are considered to be "on-device" and are thus not affected by the requirements of VIRTIO_F_ACCESS_PLATFORM' into *both* the MMIO and PCI transport docs? But then it's basically just saying the same thing in two different locations? I don't think we're debating what the actual implementations should *do* ... are we? To me it's obvious that what I'm trying to say here *should* always be true. 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