From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lu Baolu Subject: Re: [RFC PATCH v2 08/10] vfio/type1: Add domain at(de)taching group helpers Date: Wed, 26 Sep 2018 10:11:03 +0800 Message-ID: <1b4c12c3-1dc2-d9ba-9ba4-5220db3e2302@linux.intel.com> References: <20180830040922.30426-1-baolu.lu@linux.intel.com> <20180830040922.30426-9-baolu.lu@linux.intel.com> <04f5dc9d-71b1-37ec-402b-fae5f9e08664@arm.com> <75517c87-6ffd-2023-a541-3c69ae52ef4b@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <75517c87-6ffd-2023-a541-3c69ae52ef4b@arm.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Jean-Philippe Brucker , "Tian, Kevin" , Joerg Roedel , David Woodhouse , Alex Williamson , Kirti Wankhede Cc: baolu.lu@linux.intel.com, "Raj, Ashok" , "Bie, Tiwei" , "Kumar, Sanjay K" , "iommu@lists.linux-foundation.org" , "linux-kernel@vger.kernel.org" , "Sun, Yi Y" , "Pan, Jacob jun" , "kvm@vger.kernel.org" List-Id: iommu@lists.linux-foundation.org Hi, On 09/26/2018 01:55 AM, Jean-Philippe Brucker wrote: > On 19/09/2018 00:26, Tian, Kevin wrote: >>> If the core actually calls it, we can implement detach_dev :) The >>> problem is that the core never calls detach_dev when default_domain is >>> present (affects any IOMMU driver that relies on default_domain, >>> including AMD), and even in case 4) the default_domain is present for >>> the parent device >> >> Then can we change that core logic so detach_dev is invoked in all >> cases? yes there will be some changes in vendor drivers, but I expect >> this change trivial (especially considering the gain in IOMMU API >> simplicity side as described below). > > Thinking more about this, there might be a way that doesn't require too > much rewriting of IOMMU drivers. When VFIO calls iommu_detach_group to > detach a vfio-pci device from its domain, it could do detach_dev(dev, > old_domain) followed by attach_dev(dev, default_domain) instead of only > attach_dev(dev, default_domain), so: > > __iommu_attach_group(grp, unmanaged_domain) > ops->attach_dev(dev, unmanaged_domain) > -> IOMMU driver detaches from default_domain only if the dev isn't > in auxiliary mode > > __iommu_detach_group(grp, unmanaged_domain) > if (ops->detach_dev) > ops->detach_dev(dev, unmanaged_domain) > ops->attach_dev(dev, default_domain) > -> IOMMU driver ignores this if still attached to default_domain > This looks good to me. Just a minor change to make it more readable. __iommu_detach_group(grp, unmanaged_domain) if (ops->detach_dev) ops->detach_dev(dev, unmanaged_domain) if (default_domain) ops->attach_dev(dev, default_domain) Best regards, Lu Baolu > It's not trivial: since half the IOMMU drivers seem to be using default > domain now, their detach_dev callback might have been dead code for a > while (I can't find a path where it still gets called), so re-enabling > it requires some attention. However, since most of them won't care about > aux domains, maybe we could just remove their detach_dev pointer. > > The resulting logic of attach/detach_dev in IOMMU drivers that do use > aux domains still seems unnecessarily convoluted. It could as well be > done with separate attach_aux/detach_aux functions. If you want to keep > it that way though, I think the above could work for us and I'll try to > write an RFC. > > Thanks, > Jean >