From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id ACAAD606A326 for ; Thu, 5 Nov 2026 18:21:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=lists.infradead.org header.i=@lists.infradead.org header.a=rsa-sha256 header.s=bombadil.20210309 header.b=C5/bZ319; dkim=pass (2048-bit key, unprotected) header.d=ziepe.ca header.i=@ziepe.ca header.a=rsa-sha256 header.s=google header.b=WDDOju96 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Unsubscribe-Post:List-Owner; bh=jskhMrN6L8/ity8GI6Per+nZ8wI0zDQt0quVEnFZ+Iw=; b=C5/bZ319uiYEnh0sLbflPgZuMc wlFnlJ5kzD0c/DvkSTe6F8yxyyvC9Mmk6H8vrvak0PPx7YbcObIOEnU++0ujR34bAIcu4UuS8WKp/ uVEgbF0gGDsJ0qMcuupo34tWbrSaXp0lb4whwJapOO+6lCkFm/nwRasEg/CIDA6cWbeZO2jfFE6MG dmCYeDgHNfbLvdr96xP/izsT5LZthggigfcRbtFD6GlRYy5cFqBNPUmWAh2Ip6Vb7hbNTf/euQuEp SuGiNpk5WYg0o9/prnJzzOaAor4rI2PohGQTdIlyIur91NacMbM1CN5yD3WwmMDjOTAvCgWNdS+cM tPamab0w==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.100.1 #2 (Red Hat Linux)) id 1xP25X-0000000A7L1-0yeS; Thu, 05 Nov 2026 18:21:29 +0000 Received: from mail-vs1-xe2f.google.com ([2607:f8b0:4864:20::e2f]) by bombadil.infradead.org with esmtps (Exim 4.100.1 #2 (Red Hat Linux)) id 1xP25F-0000000A7Ji-0PAk for linux-arm-kernel@lists.infradead.org; Thu, 05 Nov 2026 18:21:21 +0000 Received: by mail-vs1-xe2f.google.com with SMTP id ada2fe7eead31-7c3b6e8225dso1406165137.2 for ; Thu, 05 Nov 2026 10:21:08 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ziepe.ca; s=google; t=1793902868; x=1794507668; darn=lists.infradead.org; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:from:to:cc:subject :date:message-id:reply-to:content-type; bh=jskhMrN6L8/ity8GI6Per+nZ8wI0zDQt0quVEnFZ+Iw=; b=WDDOju96nEJSgKGMk7X9i2tx851MW7q5K/SAR2LFL1/bRQznjkDXo+VJOx0BSLDM8u rRQwpyISfz5ZgacrRpt0Z3V14Cf7Y8bezXa05xnZZpS9hB4Sh0MixvEa4NsiawXF9B5l iFMi7nvmvEFlVxEZmixYrhc1zU7aZ2fcXwaYpB+04dcqE9YYR43pX7zkNNL/SnqEgX4v mjJQVo3Wc+tS/b3bo8UMaVDxNID7vukcaUGcXjAKOpErVDYuIEvMdn6Bd5rLndXmhAJW YkA2SGjWZ/07gGbbTJo5XA91lyzy0UdzaiXq1L+cjPUj7VTch0mIG8+uS7PouC+EHbYi 3tJg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1793902868; x=1794507668; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=jskhMrN6L8/ity8GI6Per+nZ8wI0zDQt0quVEnFZ+Iw=; b=jYHAOybVP2Ifyi4cZZHwfafrsyh44TAf9WmT0qzIONacx14TaK4CEcr9V32N0rL/ix vbO7mBln6aqg4dNOyJAgb4VHpgdH8TJbxP04Ny3paPKCzNu63mzp6Ee6yYv/zvR2T4AG cLpHkpkGCIb4ZJbPntHiwtJwjEAx9NKWzOOLHsTxH9+/jQ/d/oarjVwlvC5R8bzOR0w3 7qFklvLkvgmm8J0rZ1wQ0/pKonRmkszX+tdlNdMsaNWkju9c4wQ6ZjkIA1Tmz6QSfzGY H0HuF1OmAb7g0DRq9YOFzP8XB66+W04lILuyAoTofAPULUgl5svErYtfytOoGKxxao8J DbZA== X-Forwarded-Encrypted: i=1; AKwUvBxgtw3EX8c+5fzRPDx5WEKG8st+qqfQX6P7xktR+H6MTH1Jr5fpxgWQRPebj7bFqFZ5F1yMHKIpgve/O0S8cBcx@lists.infradead.org X-Gm-Message-State: APuU4Z/bPn88dwX4YywOoPQktZMDuKoirSaJpy7kwch2c0EPghjBqgrz tirvECIV54ZKQGMDGE27su9SXwL15z4j80L8nNyr4a0eoPbzamI6iAumgG9bQbZ4R8g= X-Gm-Gg: AYBFou2YbT9zxUS2aDIyaCrAATn5b+kKz7as7q0ax9vEnTa7pk1MKcrHZcn1V/HiikH nPTW19UAGeNtbBOHL2CxYLNnuS0I9BEIygglrCAOzRmgKR95Mm9vPf1biS5bOYLGkiOGjAX8hSf wul1yoNV5Nrex5WCZEBzlO9ieguxn9MXPi6tI25K0mkuhoKx16rVrnP5D/NKknPm2mtDw+rf4ER Fo1Xks63rsRSC5Y8JBY9Qcv0ELW3byViqbmZDQZmz9KRb/fRTcBf96eEwaxaBFaF7w1CH7ueU1p c8o70lDPRwgi0R67tz442BTYEcbX+d3lvritfwcX+ycIp0wtZo++1o5P0IcY494Q32lTEWeZFdF 2fn+choMMpXZ6BzkM6pEnvbCtlcRd6tN3ktktvYf4r2bxVmoo7F8laguBuvVFHcm5k3nNPOvwp8 YLNXA7yKjHwrgcrOFplYIgO/anWaCNJUKra4eZHVjb2RvYWeCoYutUrnhMyGjOynD44KfIGHWv1 giFubd/CzjT7ogB4Ccqbh+BPkAosLIEOdfS1hsbZd6+NHPZJTtYMkyAlruCtgrQ6DHdy8a+DXl+ vqLpAbhwOohimBBAB4rMkQbeL7b5uvPq5Y4SBpFvLe+m6VbLqa2sOWLbspK2I8RRUJ1xxXssI1h vecGJL1ZWDg== X-Received: by 2002:a05:6102:5706:b0:7cc:2712:caf2 with SMTP id ada2fe7eead31-7d2a1628b19mr348440137.23.1793902867469; Thu, 05 Nov 2026 10:21:07 -0800 (PST) Received: from ziepe.ca (hlfxns010zw-159-2-239-150.pppoe-dynamic.high-speed.ns.bellaliant.net. [159.2.239.150]) by smtp.gmail.com with ESMTPSA id a1e0cc1a2514c-998da178b59sm5242293241.12.2026.11.05.10.21.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 Nov 2026 10:21:06 -0800 (PST) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1xP25C-00000003LsF-0vAz; Thu, 05 Nov 2026 14:21:06 -0400 Date: Thu, 5 Nov 2026 14:21:06 -0400 From: Jason Gunthorpe To: Nicolin Chen Cc: "Aneesh Kumar K.V" , iommu@lists.linux.dev, Alex Williamson , Alexey Kardashevskiy , Bjorn Helgaas , Catalin Marinas , Jacob Pan , Joerg Roedel , Jonathan Cameron , Jonathan Hunter , Kevin Tian , Krishna Reddy , Lukas Wunner , Robin Murphy , Samuel Ortiz , Shameer Kolothum , Steven Price , Suravee Suthikulpanit , Suzuki K Poulose , Thierry Reding , Vasant Hegde , Will Deacon , Xu Yilun , kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linux-tegra@vger.kernel.org, Jonathan Corbet , Shuah Khan , Randy Dunlap Subject: Re: [PATCH v8 13/15] iommufd/viommu: Allow vIOMMUs without a parent HWPT Message-ID: <20261105182106.GD663069@ziepe.ca> References: <20261104161632.3547423-1-aneesh.kumar@kernel.org> <20261104161632.3547423-14-aneesh.kumar@kernel.org> <20261104193139.GB3889730@ziepe.ca> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20261105_102109_764245_21D17B99 X-CRM114-Status: GOOD ( 16.28 ) X-Spam-Score: -2.1 (--) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" X-Spam-Status: No, score=-5.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Thu, Nov 05, 2026 at 09:44:42AM -0800, Nicolin Chen wrote: > On Thu, Nov 05, 2026 at 10:58:06AM +0530, Aneesh Kumar K.V wrote: > > Jason Gunthorpe writes: > > > On Wed, Nov 04, 2026 at 11:03:41AM -0800, Nicolin Chen wrote: > > >> By dropping the nesting parent from VIOMMU, it just simplifies the > > >> attachment to an S1 paging hwpt, right? > > > > > > Yes. > > > > > > The VMM must always maintain a S1 paging attachment that is the > > > identity map of the VM on all devices, same action as when there is no > > > viommu. > > > > > > > I am currently creating an S2 paging attachment. This results in a > > configuration with S1 disabled and S2 enabled, which is used by all > > untrusted devices. > > For validation, that would work. Yet "no viommu" should would be S1 > paging, i.e. hwpt allocated without IOMMU_HWPT_ALLOC_NEST_PARENT. It doesn't matter, consistently using a single S2 for everything is probably better.. The VMM should try to minimize the number of hwpts involved, ideally just one per NUMA Jason