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 C9D7A606A31B for ; Fri, 23 Oct 2026 14:29:22 +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=pLPNkcfT; dkim=pass (2048-bit key, unprotected) header.d=ziepe.ca header.i=@ziepe.ca header.a=rsa-sha256 header.s=google header.b=hdE9z3GR 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=MtqXElKTNCKa651mdJkZvNuV+haZHv7iacPGuZotGd8=; b=pLPNkcfTICB4SY5JFuAjxW614A OoWQ3zDp54KQr0p1xRd83mqAsXtyE0zwelpyTMpZtgiAG0tSgbR7Gs8j3LtjoeVIfw8wvQYn73J/X rcq72lxlCAdhcY6o+IOt/wJMWCETcPwvYqGrHrIpaxmGcu036xYNMm4NYjvSGw3aBoexmQ8IF1Hro BoiFUtESFrvNpJtZtMEMX2lrjqjNxK0tGpl2UQuB25FKyzhdGByjkR8eoGSVZeXwFL8MT+Y1++uJR W5+JZMeVnzyecDKktFibsn/Nt82/l1L6Brs+I6IkTGXN1W8K8Ep+q7Nb+wwSGYKua5I4t4uXxsYXD cemdekiQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.100.1 #2 (Red Hat Linux)) id 1xKGGh-0000000GWGv-29iF; Fri, 23 Oct 2026 14:29:15 +0000 Received: from mail-qk1-x72f.google.com ([2607:f8b0:4864:20::72f]) by bombadil.infradead.org with esmtps (Exim 4.100.1 #2 (Red Hat Linux)) id 1xKGGe-0000000GWGX-1JXm for linux-arm-kernel@lists.infradead.org; Fri, 23 Oct 2026 14:29:14 +0000 Received: by mail-qk1-x72f.google.com with SMTP id af79cd13be357-93e7ad9f78dso106060985a.1 for ; Fri, 23 Oct 2026 07:29:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ziepe.ca; s=google; t=1792765751; x=1793370551; 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=MtqXElKTNCKa651mdJkZvNuV+haZHv7iacPGuZotGd8=; b=hdE9z3GRlTs97QuUO72lWSZ4b12nvuj5usLta9GtsXmH6pFn2cpFAz2tyHGmzQfc2/ xWNejNWwlqlLvSPoWOlzqcwNTCNPJQ34TfqUwcP5Ayd51q8ruRsUI2ClNOdKUU3/k6Ho AV3vANk+2nTpCkz5jqPth6hRbmE8Q409VC9nAFcEd5EEjisGHj3ZTvmEwfOmO0wJcoeJ 9t8ORvfh85mM0HZz4bgmzUHf0SXwn72RMVMnGChqN7KjhCVuDcHI8wJpbnvZnt4hdHYJ +IYKRcbWGSDWsP6hA4HK9WsdY/eNlmwstDz13mSX/dmYZnOwN3uO+JQpWUxQ9VDUwJZW DmsQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1792765751; x=1793370551; 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=MtqXElKTNCKa651mdJkZvNuV+haZHv7iacPGuZotGd8=; b=TsW+YnCrFMsBPHosvp30ncGukb/aYQxcCM2ggkaGGdZZvCCGjNMSU2HP/J6iwSA+t7 x4x3JHmuYhnrBiTQdvj9yoJ9aQSwIroZ3lxZ+4mjBF8EEOKBvjeQT2Ue/YWLF6ykWaRE 7AFq8nlUYCgYqZABXSUcg3Niaid8x5gL3kWJcBxjUxO++7IX01wUAjU6ykWQupbzp8fE /R8OiDp/XYwUDyXpI4sftjQhL86daDrbxb2+PVaFLoX2SuHN/7PekRCrvnaysYU1CaZX wZlc+gty7zNBWNfl9FNyvdKyKjwFbs1yiQbTVxG7j4s0/W96vwKxzV/LuBgJGHf8F5j8 aMdw== X-Forwarded-Encrypted: i=1; AKwUvBys/W6vh+Ok57Xzuyt1yCNdynW/xTca9sR6GjOvE54RnRMAS2H+pQjrAD+86v+Zr3mQUNaplk0L8zuLutUbfG4y@lists.infradead.org X-Gm-Message-State: AFq9FYKzopr3RE3Pgxt0Zps71qHulwEZqcE3LVMDhiKKX47H64NNtwDm Wz8zEKbR4dSAios/6mKbXehmSpuOwDse0DHsAPA73y6mDDwzyxo5r4eTeqjaMLzJUrw= X-Gm-Gg: AYBFou0793tgIvAsqbk4vOYCim8MFpuCRM8h7m/P2s7NRClz4CChbgrxCzYCm89dCCy qwJnldggaGDxuznwESW2qss8JRRnEQNmsSsa1IFGduPOk2JBcfKTgiprwjzZZh0bDmNsL4DtLs4 zDhEV0GbDCXMI5hW44/mADWKBezwnY+X97K7HaSznSRKHHr9laSBiP6l5PqoS5kusfTt7O86WzX bkpkZF8Vyk6WMFOeQjlJFhV3oLcxxd1x70lnpOCcUBdwmAVa2gMLVXPBz8etY5rC++mFa0C4z9n n4S3LVog2mSLj2Wb2d/KUZWi1mYqWMe9HeNNRD6X3VqA7OJfrDVrgo5fV0Vc6p6ytFhJNqs5X6w bda4oRWNZqSjLe1OVLx5+bZSl+oLVQZjyC0svNdJB7ryb4U1yrlfaKPSeo8ed7ZhyZoKSoDpNNW BLNeew50eNsgO3C0sgzcQ9vf/NZ8gKeWB08LiB6XyWOmxgjdV4lZD0Xc/X+eLSOIu51q9tZv2/2 korw+TRwa/U1wxS5UFizxS9UVkYsGqy23yeDmdmcxcq+KHnxN3fUfk4jByPP/EOTTuL/DQAgZK9 KpwSSVpnTE2SIxv9luw06SxrVvltpvOwfabdhw== X-Received: by 2002:a05:620a:7001:b0:939:b057:daf2 with SMTP id af79cd13be357-93f6f7fef1amr427452285a.45.1792765750875; Fri, 23 Oct 2026 07:29:10 -0700 (PDT) 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 af79cd13be357-9404722bccbsm30639685a.8.2026.10.23.07.29.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 23 Oct 2026 07:29:10 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1xKGGb-0000000GjTu-3HLf; Fri, 23 Oct 2026 11:29:09 -0300 Date: Fri, 23 Oct 2026 11:29:09 -0300 From: Jason Gunthorpe To: Robin Murphy Cc: Samiullah Khawaja , Joerg Roedel , Will Deacon , Kevin Tian , Alex Williamson , iommu@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Pasha Tatashin , David Matlack , Lu Baolu , Pranjal Shrivastava Subject: Re: [RFC PATCH 3/3] iommu/arm-smmu-v3: Add support for hitless replace of S1 domains Message-ID: <20261023142909.GG3977851@ziepe.ca> References: <20260925011308.3381953-1-skhawaja@google.com> <20260925011308.3381953-4-skhawaja@google.com> <3d1eb92f-3447-49f0-a210-fd4fa015304b@arm.com> <20261023134900.GB3977851@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-20261023_072913_318364_2B53A202 X-CRM114-Status: GOOD ( 17.89 ) 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=-11.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=ham 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 Fri, Oct 23, 2026 at 03:04:23PM +0100, Robin Murphy wrote: > On 23/10/2026 2:49 pm, Jason Gunthorpe wrote: > > On Fri, Oct 23, 2026 at 02:43:28PM +0100, Robin Murphy wrote: > > > > @@ -3664,8 +3726,8 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev, > > > > struct arm_smmu_cd target_cd; > > > > arm_smmu_make_s1_cd(&target_cd, master, smmu_domain); > > > > - arm_smmu_write_cd_entry(master, IOMMU_NO_PASID, cdptr, > > > > - &target_cd); > > > > + arm_smmu_replace_cd_entry(master, IOMMU_NO_PASID, cdptr, > > > > + &target_cd); > > > > > > No, we cannot blindly do this for arbitrary ->attach_dev calls - the > > > majority of S1->S1 transitions are going to be moving back and forth between > > > the default domain and user domains, where there is zero expectation, let > > > alone guarantee, that the translations would be equivalent and thus not > > > liable to lead to TLB conflict aborts or amalgamation hell. > > > > Heh, yeah this probably only works properly with BBML2 or something so > > the temporary ASID doesn't explode. > > This is fundamental VMSA behaviour - see R_FVQCK in the Arm ARM. BBML only > applies to the one specific case of identical VA->PA translations with > identical attributes _only_ differing in the leaf level at which they are > described. Sigh, I thought ARM got past that 'tlb conflicts catch fire'. So, yeah we need a flag that says "I pinky swear these are identical translations". And it has to be a kernel only flag since we can't let userspace trigger this. Jason