From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from fout3-smtp.messagingengine.com (fout3-smtp.messagingengine.com [103.168.172.146]) (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 D650B7A151 for ; Fri, 22 Mar 2024 19:52:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=103.168.172.146 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711137179; cv=none; b=YKzk5u7gk1XfiYS7vXzbqisa3nbkcrSneReQJ8fYowiaMncbz1dLildgaufjmuBhwdUQLGuGMxHtdMjGfNWBrutwIJ5kbj4jBcHJitkrt65UXfroxsyjWRLGEc2cioi3a20Fb8K0IbaLTVuCI4ycw4sMkQA3sdkCGlWLaxOePUc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711137179; c=relaxed/simple; bh=882W7BvtwuGGMvjQvWUlxevdudIOvEYZS9sbSSNidg0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Ulrt+3ZNldUlt0ShP58SpXcwnXsNqtlq3yv44sbN4FSwhwO6ZToHix3Y+IeXx80n7mLttAypX997nAfKrxQgOMz2GazyrkRI2OcFRB49XU4JTQUYYl5BwUmYFdUgqrac9hTErWLnsBMl89DSKgNtw5osA4qHExyMDlwRlK8yodQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=tyhicks.com; spf=pass smtp.mailfrom=tyhicks.com; dkim=pass (2048-bit key) header.d=tyhicks.com header.i=@tyhicks.com header.b=HvCYZyr5; dkim=pass (2048-bit key) header.d=messagingengine.com header.i=@messagingengine.com header.b=Rj6wfpM1; arc=none smtp.client-ip=103.168.172.146 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=tyhicks.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=tyhicks.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=tyhicks.com header.i=@tyhicks.com header.b="HvCYZyr5"; dkim=pass (2048-bit key) header.d=messagingengine.com header.i=@messagingengine.com header.b="Rj6wfpM1" Received: from compute2.internal (compute2.nyi.internal [10.202.2.46]) by mailfout.nyi.internal (Postfix) with ESMTP id 147B913800EE; Fri, 22 Mar 2024 15:52:57 -0400 (EDT) Received: from mailfrontend1 ([10.202.2.162]) by compute2.internal (MEProxy); Fri, 22 Mar 2024 15:52:57 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=tyhicks.com; h= cc:cc:content-type:content-type:date:date:from:from:in-reply-to :in-reply-to:message-id:mime-version:references:reply-to:subject :subject:to:to; s=fm1; t=1711137177; x=1711223577; bh=SDe9rNbXis 2QKNa9pGytu06HZGUqYjzBkgt7/9/1dz8=; b=HvCYZyr5O3L/UydCTC5xfpLLy3 KqBlUl4a1x1yS2iMt+r4mpd7R0OzkQMWuqUlCOm879HnJaGq65Trchp+6wc5fI92 U7oiN7k1K10otaVkFjDuFz8ul528JNpjl+ehVIEIAB6Oamp3J0uqGOaE5vtul276 MvwMKoi7TgeRmO3d0RLaq9h27YrlsfutW75c8FAF/Z/UOFUZB8PX36bCeyvZlc30 5ZQlOZqWXmQ4vmWTVREIb+AQdLPy6jB5jLTcVGKHZKWHo5UMrw7+B+HH48Yx3LXj bwlQ/+SLZAlyaCb+aXBvFw0cyz+SN/OeeKJDq4LwLb8GtlP0rv6CB7fpIc4g== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:cc:content-type:content-type:date:date :feedback-id:feedback-id:from:from:in-reply-to:in-reply-to :message-id:mime-version:references:reply-to:subject:subject:to :to:x-me-proxy:x-me-proxy:x-me-sender:x-me-sender:x-sasl-enc; s= fm2; t=1711137177; x=1711223577; bh=SDe9rNbXis2QKNa9pGytu06HZGUq YjzBkgt7/9/1dz8=; b=Rj6wfpM1eqRiPgpB3/qkn1p4txZDVo3Gcuix4+CvR0s0 LyMFGwXmfdGrD8hg5u8sB6gLeqOyvon3JJRQjiURCIeqkmOV880Qo8hkfN3zZvX6 7U6C0KlTwR+BNYRdXDSKmAFTH8l62k2cgmfDIy/G1qiwCigQFxtr5DFJLi+D0N6L K/bUC+LjfWJ5mE1jEAhu6SzeyOLY3UYM1igfZO5ObAt4NNwkBDIza1ILhm7F/1GT 7pOOVDQBXd5uG3vH4AhdCHHbPAOzK4dR82lVdByL7MVlP3gkA/n4wR2aqUqkFfCK +P/8t/uGREghrQYpvI6eAB2BbrdkqCxVRGlhJvufwQ== X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvledruddtvddgieeiucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne cujfgurhepfffhvfevuffkfhggtggujgesthdtredttddtvdenucfhrhhomhepvfihlhgv rhcujfhitghkshcuoegtohguvgesthihhhhitghkshdrtghomheqnecuggftrfgrthhtvg hrnhepvdehvddttdfhfefhtdfgleehfeeggfdujeeuveekudevkedvgeejtddtfefgleei necuvehluhhsthgvrhfuihiivgeptdenucfrrghrrghmpehmrghilhhfrhhomheptghoug gvsehthihhihgtkhhsrdgtohhm X-ME-Proxy: Feedback-ID: i78e14604:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Fri, 22 Mar 2024 15:52:55 -0400 (EDT) Date: Fri, 22 Mar 2024 14:52:52 -0500 From: Tyler Hicks To: Will Deacon Cc: Jason Gunthorpe , Robin Murphy , Jerry Snitselaar , linux-arm-kernel@lists.infradead.org, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, Dexuan Cui , Easwar Hariharan Subject: Re: Why is the ARM SMMU v1/v2 put into bypass mode on kexec? Message-ID: References: <120d0dec-450f-41f8-9e05-fd763e84f6dd@arm.com> <20240319154756.GB2901@willie-the-truck> <20240319175007.GC66976@ziepe.ca> <20240322155529.GE5634@willie-the-truck> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240322155529.GE5634@willie-the-truck> On 2024-03-22 15:55:29, Will Deacon wrote: > Hey Jason, > > On Tue, Mar 19, 2024 at 02:50:07PM -0300, Jason Gunthorpe wrote: > > On Tue, Mar 19, 2024 at 03:47:56PM +0000, Will Deacon wrote: > > > > > Right, it's hard to win if DMA-active devices weren't quiesced properly > > > by the outgoing kernel. Either the SMMU was left in abort (leading to the > > > problems you list above) or the SMMU is left in bypass (leading to possible > > > data corruption). Which is better? > > > > For whatever reason (and I really don't like this design) alot of work > > was done on x86 so that device continues to work as-was right up until > > the crash kernel does the first DMA operation. Including having the > > crash kernel non disruptively inherit and retain the IOMMU > > configuration. (eg see translation_pre_enabled() stuff in intel > > driver) > > Right, I'm also not thrilled about trying to implement that :) > What we have at the moment seems to be good enough to avoid folks > complaining about it. > > For the case Tyler is reporting, though, I _think_ it's just a standard > kexec() rather than a crashkernel. That's correct. Tyler