From nobody Mon Jun 8 16:30:47 2026 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 3AD551940B0; Thu, 28 May 2026 05:46:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.133 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779947186; cv=none; b=j+UxHBWKJKbv8QFSQ5L7OyE/aNsYW+r7aVqmtCubZ0E7jCQXbvpwVPqREOQuqSUs9WlOveEyxGKHHpDYkYvnQiafqwNBA0krVcP+E2jHxAMjVbvnUsl1TxDgvLRXjDBsTbjA6mGN4pDz9V2WmpVgkh39V3uSzKRPR+wiiuRypNc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779947186; c=relaxed/simple; bh=vRplcPPetVrP41t9VSybTHS8jAdvhvc/utVsjAH6HOo=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=rfppKuwa2tm3viw/k0wy1fdgAbFTjDPI8lJE5hp6NH89b5n8qDba/WW7c2K6IQA5dG9Vv3P9uPK7GkJCaIKMPNlSUzfNElpuoQeGjYYjJr/M1FZ2Pehtfl9vVIEMZAliAUcvc+uJLYDLvrDwiT2QuqdmFbTc1PmO8+KnKIhxHbM= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=xVlWgDX/; arc=none smtp.client-ip=198.137.202.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="xVlWgDX/" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=Content-Transfer-Encoding: MIME-Version:Message-ID:Date:Subject:Cc:To:From:Sender:Reply-To:Content-Type: Content-ID:Content-Description:In-Reply-To:References; bh=PjXuJQaHKPAZNAO+ZnE/uu4HDeWWeRJ7hBGHk01iNq0=; b=xVlWgDX/8ECEyuaGDngqYtcU02 AkQ11NX0Mo7KeR4uIjQglim7quo5/a1Ab3B8BQh1yj6pM3R0p9BmzezSZ+cU3YUjZFKCvpzeq+dAM 9BN5eQV92rsm7SYZ5baZXI8ODI9MDc+BfCZt2pkwYbfhltpvAP2oWnYEC6N0qvwBrXoF6B1Ll5I5L gpnkEK34ol/joGNBygbsgGsaXFp0WgU1Xo3wVZ735edkoP7C7eDnk6YdENi/G24Nv+cRmC1/eOKsY Y0TrSpqZyV4FvewmMmsJU6QC87BdiuyfrDLYQynLgi/gQmvW6AiMUNyunPWkMm1CaJKkxtpJ7Mxz2 k60FLnAA==; Received: from [50.53.43.113] (helo=bombadil.infradead.org) by bombadil.infradead.org with esmtpsa (Exim 4.99.1 #2 (Red Hat Linux)) id 1wSTZN-000000059ys-1IH7; Thu, 28 May 2026 05:46:13 +0000 From: Randy Dunlap To: linux-kernel@vger.kernel.org Cc: Randy Dunlap , Jonathan Corbet , Shuah Khan , linux-doc@vger.kernel.org, Joerg Roedel , Will Deacon , Robin Murphy , iommu@lists.linux.dev, Borislav Petkov Subject: [PATCH] iommu: Documentation: rearrange, update kernel-parameters Date: Wed, 27 May 2026 22:46:11 -0700 Message-ID: <20260528054611.1524937-1-rdunlap@infradead.org> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Add text for some undescribed iommu=3D parameters (merge, nomerge, biomerge, panic, nopanic, pt, nopt). Add "usedac" and its description. Add that iommu=3Dpt is equivalent to iommu.passthrough=3D1 and that iommu=3Dnopt is equivalent to iommu.passthrough=3D0. Move the PPC/POWERNV heading & its option "nobypass" to a separate area since the current "iommu=3D" applies only to X86 (according to its heading). Unindent the AMD GART IOMMU options heading to make it stand out. Also add its kconfig symbol name to be explicit about what these options apply to. Make sure that the IOMMU options that are listed under AMD Gart HW IOMMU-specific options are only for that product; i.e., add "force" there and move "merge", "nomerge", and "panic" to the general IOMMU options area. Signed-off-by: Randy Dunlap --- NB: Wording suggestions welcome. Cc: Jonathan Corbet Cc: Shuah Khan Cc: linux-doc@vger.kernel.org Cc: Joerg Roedel Cc: Will Deacon Cc: Robin Murphy Cc: iommu@lists.linux.dev Cc: Borislav Petkov Documentation/admin-guide/kernel-parameters.txt | 48 +++++++++----- 1 file changed, 32 insertions(+), 16 deletions(-) --- linux-next-20260527.orig/Documentation/admin-guide/kernel-parameters.txt +++ linux-next-20260527/Documentation/admin-guide/kernel-parameters.txt @@ -2548,23 +2548,41 @@ Kernel parameters Don't force hardware IOMMU usage when it is not needed. (default). =20 + merge + Do scatter-gather (SG) merging. Implies "force" + (experimental). + + nomerge + Don't do scatter-gather (SG) merging. + biomerge + Do scatter-gather (SG) merging. Implies "force" + (experimental). [same as "merge"] + panic + Always panic when IOMMU overflows. + nopanic - merge - nomerge + Don't panic on IOMMU overflows. + + pt + Use passththrough mode by default + (Equivalent to iommu.passthrough=3D1) + + nopt + Use translated mode for DMA by default + (Equivalent to iommu.passthrough=3D0) =20 soft Use software bounce buffering (SWIOTLB) (default for Intel machines). This can be used to prevent the usage of an available hardware IOMMU. =20 - pt - nopt - nobypass [PPC/POWERNV] - Disable IOMMU bypass, using IOMMU for PCI devices. + usedac + Use the DAC on VIA PCI bridge + (default: disable the VIA PCI bridge DAC) =20 - AMD Gart HW IOMMU-specific options: + AMD Gart HW IOMMU-specific options: (CONFIG_GART_IOMMU) =20 Set the size of the remapping area in bytes. @@ -2572,6 +2590,9 @@ Kernel parameters allowed Overwrite iommu off workarounds for specific chipsets =20 + force + Overwrite iommu off workarounds for specific chipsets + fullflush Flush IOMMU on each allocation (default). =20 @@ -2582,21 +2603,16 @@ Kernel parameters Allocate an own aperture over RAM with size 32MB<