From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mga02.intel.com (mga02.intel.com [134.134.136.20]) (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 E8C22C2FD for ; Fri, 5 May 2023 20:27:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1683318469; x=1714854469; h=date:from:to:cc:subject:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=attubp1Y5SHGM2s6fxrjpGYDxEhvZVo+MggS/87KNmo=; b=FjfUhCedrxP784QCxeBwELgUqjkrkjiTXXIpmTxbPQxcRUxASnJzioAW AK2IxM9ZBKl0hL4hKlTS/Dmwe1sK6YT5ZvV7b4OajTU4AIPQTVOXKMG9E RNb5rHCwEGEsJMtUGP5+Rtodtns/aVJry9gEMIB4e6OC9XMRBBghQ8SiR NLDtCTsk+LmbwxfmMRtWET3AjGowDXExA9W3TLodzfvONpkUaJude1F/Z L0K1TE1v31uVxjugQggm74PIg1KohgPtWeli5VHOMjXhIoo1NExM8IYSB 6zVzhD6BQXwSCWh05IW4mVR2Wsp6qB6BsoAQJM2J1fDAvjg3PRWM7aYfX A==; X-IronPort-AV: E=McAfee;i="6600,9927,10701"; a="338495576" X-IronPort-AV: E=Sophos;i="5.99,253,1677571200"; d="scan'208";a="338495576" Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 May 2023 13:27:40 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10701"; a="767259577" X-IronPort-AV: E=Sophos;i="5.99,253,1677571200"; d="scan'208";a="767259577" Received: from jacob-builder.jf.intel.com (HELO jacob-builder) ([10.24.100.114]) by fmsmga004-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 May 2023 13:27:39 -0700 Date: Fri, 5 May 2023 13:32:02 -0700 From: Jacob Pan To: Baolu Lu Cc: LKML , iommu@lists.linux.dev, Robin Murphy , Jason Gunthorpe , Joerg Roedel , dmaengine@vger.kernel.org, vkoul@kernel.org, Will Deacon , David Woodhouse , Raj Ashok , "Tian, Kevin" , Yi Liu , "Yu, Fenghua" , Dave Jiang , Tony Luck , "Zanussi, Tom" , narayan.ranganathan@intel.com, jacob.jun.pan@linux.intel.com Subject: Re: [PATCH v5 6/7] iommu/vt-d: Implement set_dev_pasid domain op Message-ID: <20230505133202.094bf8be@jacob-builder> In-Reply-To: <35ceffc2-e306-6215-e90a-43548f6feca6@linux.intel.com> References: <20230427174937.471668-1-jacob.jun.pan@linux.intel.com> <20230427174937.471668-7-jacob.jun.pan@linux.intel.com> <76c98e62-1cac-2ab6-7721-08ec2c1fceb8@linux.intel.com> <20230504160334.496085db@jacob-builder> <35ceffc2-e306-6215-e90a-43548f6feca6@linux.intel.com> Organization: OTC X-Mailer: Claws Mail 3.17.5 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Hi Baolu, On Fri, 5 May 2023 10:58:38 +0800, Baolu Lu wrote: > On 5/5/23 7:03 AM, Jacob Pan wrote: > >>> +static int intel_iommu_attach_device_pasid(struct iommu_domain > >>> *domain, > >>> + struct device *dev, > >>> ioasid_t pasid) +{ > >>> + struct device_domain_info *info = dev_iommu_priv_get(dev); > >>> + struct dmar_domain *dmar_domain = to_dmar_domain(domain); > >>> + struct intel_iommu *iommu = info->iommu; > >>> + int ret; > >>> + > >>> + if (!pasid_supported(iommu)) > >>> + return -ENODEV; > >>> + > >>> + ret = prepare_domain_attach_device(domain, dev); > >>> + if (ret) > >>> + return ret; > >>> + > >>> + /* > >>> + * Most likely the device context has already been set up, > >>> will only > >>> + * take a domain ID reference. Otherwise, device context will > >>> be set > >>> + * up here. > >> The "otherwise" case is only default domain deferred attaching case, > >> right? > > it might be the only case so far, but my intention is to be general. > > i.e. no ordering requirements. I believe it is more future proof in case > > device_attach_pasid called before device_attach. > > Let's put aside deferred attach and talk about it later. > > The device's context entry is configured when the default domain is > being attached to the device. And, the default domain attaching is in > the iommu probe_device path. It always happens before set_device_pasid > which is designed to be called by the device driver. So the real > situation is that when the device driver calls set_device_pasid, the > context entry should already have been configured. > > Then let's pick up the deferred attach case. It is a workaround for > kdump (Documentation/admin-guide/kdump/kdump.rst). I don't think PASID > feature is functionally required by any kdump capture kernel as its > main purpose is to dump the memory of a panic kernel. > > In summary, it seems to be reasonable for the vt-d driver to return > -EBUSY when a device's context was copied. The idxd driver should > continue to work without kernel DMA with PASID support. > > if (context_copied(iommu, bus, devfn)) > return -EBUSY; > > Make things general is always good, but this doesn't mean that we need > to make the code complex to support cases that do not exist or are not > used. Thoughts? > Good point, it is better not put dead code in. Let me also document this behavior for future change that may affect the ordering requirement. Thanks, Jacob