From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=217.140.110.172 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792764273; b=rz9RjxZOiLTRuwe4/EOSTWmiGiFLRMwvaBGJyNrABdOdcP9lHv731Il9FTtVRLsW5VzF iSdZHWFN8AsDOrZOEpjGkkJ40PjyK2UuLwgHCPhhGsrOXPoDE5JjqKiHx7+/DV+0ZN3/r m+Q+2RK3PdLx0qnOUIm7nT9JyCjg26wH25HQ5r0bw8/H7CHR6urfkcW73SlsvRiDiKqq8 Zump+0onJwMuq+502hyqHaANu5P8g+/QYH9IGYpfPLoxr4MQW/KferzK8tUBR4dKQp96K z6/VekN92tLb7k1wpYeucFPmHXJQPxCBn3e/E91auI0hsucarD1OqjhCMu0URxW0lfg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792764273; h=DMARC-Filter:Received:Received:DKIM-Signature:Message-ID:Date: MIME-Version:User-Agent:Subject:To:Cc:References:From: Content-Language:In-Reply-To:Content-Type:Content-Transfer-Encoding; bh=n36re4R3i8nXuM6/wGbiNDosDIqVkvFnDzUX2RMRlk0=; b=SXYdAT1EHgGpn7ZpVpj5HPn9dzFZRXz8A7TjTSslr2W9GyiKSD/BN6g03vyS0MIibbDO TSndW6fXlauzYjN9s6MZimA4RBetOC/tDHZBUTI6PnFDXI72A//0cvxK+LmPv5zSnQ5nz fCPUtV0d3L3zsl5f+6nfAy2x0vy0sLWM6JKcO66xwmzR3NilJvzacHub3IjMeWtzHUYnf w4wprzgQqJmjqnvGPgZhgk+VoC2mC/6iBelkuKy7v+PlaDMXkZd5sWleQbsIMhiXdLZxM ZpiDkvMQWrJgBQc8p6mNTJjwlkgZAO/wMFo95E89g/kE99bi0O0r+MwkAnZyOolLOwQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass header.d=arm.com header.i=@arm.com header.a=rsa-sha256 header.s=foss header.b=MNdayn29; arc=none smtp.remote-ip=217.140.110.172 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 3BB2C606A31D for ; Fri, 23 Oct 2026 14:04:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 3BB2C606A31D Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=arm.com header.i=@arm.com header.a=rsa-sha256 header.s=foss header.b=MNdayn29 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4BE731C00; Fri, 23 Oct 2026 07:04:28 -0700 (PDT) Received: from [10.2.212.23] (e121345-lin.cambridge.arm.com [10.2.212.23]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AAEFB3F673; Fri, 23 Oct 2026 07:04:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1792764271; bh=5LUMkx86sW2CCaNHvIGxIW+K+1BbJjEkbPwVzal5v8s=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=MNdayn29iT3ViLmPTZMzRluVsO7PfHn4zcOiCsLLTysTzD3Cs6MS/MP6pzsZOeyIa i8F1Y57RsdzBNTeLzkb4acyVsYrD+fVBCmNLNS+yasI6jOzTLjW3d0QIGG2glwXWi0 PECjFLAvvaYmEV+lv2hDunZXOn2GftZHeKRfHFBc= Message-ID: Date: Fri, 23 Oct 2026 15:04:23 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 3/3] iommu/arm-smmu-v3: Add support for hitless replace of S1 domains To: Jason Gunthorpe 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 References: <20260925011308.3381953-1-skhawaja@google.com> <20260925011308.3381953-4-skhawaja@google.com> <3d1eb92f-3447-49f0-a210-fd4fa015304b@arm.com> <20261023134900.GB3977851@ziepe.ca> From: Robin Murphy Content-Language: en-GB In-Reply-To: <20261023134900.GB3977851@ziepe.ca> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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. Thanks, Robin.