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Thu, 30 Jul 2020 21:17:04 +0000 (UTC) Received: from x1.home (ovpn-112-71.phx2.redhat.com [10.3.112.71]) by smtp.corp.redhat.com (Postfix) with ESMTP id C301519D7B; Thu, 30 Jul 2020 21:17:03 +0000 (UTC) Date: Thu, 30 Jul 2020 15:17:03 -0600 From: Alex Williamson To: Lu Baolu Cc: Joerg Roedel , Robin Murphy , Jean-Philippe Brucker , Cornelia Huck , Kevin Tian , Ashok Raj , Dave Jiang , Liu Yi L , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH v3 4/4] vfio/type1: Use iommu_aux_at(de)tach_group() APIs Message-ID: <20200730151703.5daf8ad4@x1.home> In-Reply-To: References: <20200714055703.5510-1-baolu.lu@linux.intel.com> <20200714055703.5510-5-baolu.lu@linux.intel.com> <20200729143258.22533170@x1.home> Organization: Red Hat MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, 30 Jul 2020 10:41:32 +0800 Lu Baolu wrote: > Hi Alex, > > On 7/30/20 4:32 AM, Alex Williamson wrote: > > On Tue, 14 Jul 2020 13:57:03 +0800 > > Lu Baolu wrote: > > > >> Replace iommu_aux_at(de)tach_device() with iommu_aux_at(de)tach_group(). > >> It also saves the IOMMU_DEV_FEAT_AUX-capable physcail device in the > >> vfio_group data structure so that it could be reused in other places. > >> > >> Signed-off-by: Lu Baolu > >> --- > >> drivers/vfio/vfio_iommu_type1.c | 44 ++++++--------------------------- > >> 1 file changed, 7 insertions(+), 37 deletions(-) > >> > >> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c > >> index 5e556ac9102a..f8812e68de77 100644 > >> --- a/drivers/vfio/vfio_iommu_type1.c > >> +++ b/drivers/vfio/vfio_iommu_type1.c > >> @@ -100,6 +100,7 @@ struct vfio_dma { > >> struct vfio_group { > >> struct iommu_group *iommu_group; > >> struct list_head next; > >> + struct device *iommu_device; > >> bool mdev_group; /* An mdev group */ > >> bool pinned_page_dirty_scope; > >> }; > >> @@ -1627,45 +1628,13 @@ static struct device *vfio_mdev_get_iommu_device(struct device *dev) > >> return NULL; > >> } > >> > >> -static int vfio_mdev_attach_domain(struct device *dev, void *data) > >> -{ > >> - struct iommu_domain *domain = data; > >> - struct device *iommu_device; > >> - > >> - iommu_device = vfio_mdev_get_iommu_device(dev); > >> - if (iommu_device) { > >> - if (iommu_dev_feature_enabled(iommu_device, IOMMU_DEV_FEAT_AUX)) > >> - return iommu_aux_attach_device(domain, iommu_device); > >> - else > >> - return iommu_attach_device(domain, iommu_device); > >> - } > >> - > >> - return -EINVAL; > >> -} > >> - > >> -static int vfio_mdev_detach_domain(struct device *dev, void *data) > >> -{ > >> - struct iommu_domain *domain = data; > >> - struct device *iommu_device; > >> - > >> - iommu_device = vfio_mdev_get_iommu_device(dev); > >> - if (iommu_device) { > >> - if (iommu_dev_feature_enabled(iommu_device, IOMMU_DEV_FEAT_AUX)) > >> - iommu_aux_detach_device(domain, iommu_device); > >> - else > >> - iommu_detach_device(domain, iommu_device); > >> - } > >> - > >> - return 0; > >> -} > >> - > >> static int vfio_iommu_attach_group(struct vfio_domain *domain, > >> struct vfio_group *group) > >> { > >> if (group->mdev_group) > >> - return iommu_group_for_each_dev(group->iommu_group, > >> - domain->domain, > >> - vfio_mdev_attach_domain); > >> + return iommu_aux_attach_group(domain->domain, > >> + group->iommu_group, > >> + group->iommu_device); > > > > No, we previously iterated all devices in the group and used the aux > > interface only when we have an iommu_device supporting aux. If we > > simply assume an mdev group only uses an aux domain we break existing > > users, ex. SR-IOV VF backed mdevs. Thanks, > > Oh, yes. Sorry! I didn't consider the physical device backed mdevs > cases. > > Looked into this part of code, it seems that there's a lock issue here. > The group->mutex is held in iommu_group_for_each_dev() and will be > acquired again in iommu_attach_device(). These are two different groups. We walk the devices in the mdev's group with iommu_group_for_each_dev(), holding the mdev's group lock, but we call iommu_attach_device() with iommu_device, which results in acquiring the lock for the iommu_device's group. > How about making it like: > > static int vfio_iommu_attach_group(struct vfio_domain *domain, > struct vfio_group *group) > { > if (group->mdev_group) { > struct device *iommu_device = group->iommu_device; > > if (WARN_ON(!iommu_device)) > return -EINVAL; > > if (iommu_dev_feature_enabled(iommu_device, > IOMMU_DEV_FEAT_AUX)) > return iommu_aux_attach_device(domain->domain, > iommu_device); > else > return iommu_attach_device(domain->domain, > iommu_device); > } else { > return iommu_attach_group(domain->domain, > group->iommu_group); > } > } > > The caller (vfio_iommu_type1_attach_group) has guaranteed that all mdevs > in an iommu group should be derived from a same physical device. Have we? iommu_attach_device() will fail if the group is not singleton, but that's just encouraging us to use the _attach_group() interface where the _attach_device() interface is relegated to special cases. Ideally we'd get out of those special cases and create an _attach_group() for aux that doesn't further promote these notions. > Any thoughts? See my reply to Kevin, I'm thinking we need to provide a callback that can enlighten the IOMMU layer to be able to do _attach_group() with aux or separate IOMMU backed devices. Thanks, Alex