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SubjectRe: [PATCH v5 4/8] iommu/vt-d: Aux-domain specific domain attach/detach
On Thu, 10 Jan 2019 11:00:23 +0800
Lu Baolu <baolu.lu@linux.intel.com> wrote:

> When multiple domains per device has been enabled by the
> device driver, the device will tag the default PASID for
> the domain to all DMA traffics out of the subset of this
> device; and the IOMMU should translate the DMA requests
> in PASID granularity.
>
> This adds the intel_iommu_aux_attach/detach_device() ops
> to support managing PASID granular translation structures
> when the device driver has enabled multiple domains per
> device.
>
> Cc: Ashok Raj <ashok.raj@intel.com>
> Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Cc: Kevin Tian <kevin.tian@intel.com>
> Signed-off-by: Sanjay Kumar <sanjay.k.kumar@intel.com>
> Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>

The following is probably a rather naive review given I don't know
the driver or hardware well at all. Still, it seems like things
are a lot less balanced than I'd expect and isn't totally obvious
to me why that is.

> ---
> drivers/iommu/intel-iommu.c | 152 ++++++++++++++++++++++++++++++++++++
> include/linux/intel-iommu.h | 10 +++
> 2 files changed, 162 insertions(+)
>
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index e9119d45a29d..b8fb6a4bd447 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -2482,6 +2482,7 @@ static struct dmar_domain *dmar_insert_one_dev_info(struct intel_iommu *iommu,
> info->iommu = iommu;
> info->pasid_table = NULL;
> info->auxd_enabled = 0;
> + INIT_LIST_HEAD(&info->auxiliary_domains);
>
> if (dev && dev_is_pci(dev)) {
> struct pci_dev *pdev = to_pci_dev(info->dev);
> @@ -5058,6 +5059,131 @@ static void intel_iommu_domain_free(struct iommu_domain *domain)
> domain_exit(to_dmar_domain(domain));
> }
>
> +/*
> + * Check whether a @domain could be attached to the @dev through the
> + * aux-domain attach/detach APIs.
> + */
> +static inline bool
> +is_aux_domain(struct device *dev, struct iommu_domain *domain)

I'm finding the distinction between an aux domain capability on
a given device and whether one is actually in use to be obscured
slightly in the function naming.

This one for example is actually checking if we have a domain
that is capable of being enabled for aux domain use, but not
yet actually in that mode?

Mind you I'm not sure I have a better answer for the naming.
can_aux_domain_be_enabled? is_unattached_aux_domain?



> +{
> + struct device_domain_info *info = dev->archdata.iommu;
> +
> + return info && info->auxd_enabled &&
> + domain->type == IOMMU_DOMAIN_UNMANAGED;
> +}
> +
> +static void auxiliary_link_device(struct dmar_domain *domain,
> + struct device *dev)
> +{
> + struct device_domain_info *info = dev->archdata.iommu;
> +
> + assert_spin_locked(&device_domain_lock);
> + if (WARN_ON(!info))
> + return;
> +
> + domain->auxd_refcnt++;
> + list_add(&domain->auxd, &info->auxiliary_domains);
> +}
> +
> +static void auxiliary_unlink_device(struct dmar_domain *domain,
> + struct device *dev)
> +{
> + struct device_domain_info *info = dev->archdata.iommu;
> +
> + assert_spin_locked(&device_domain_lock);
> + if (WARN_ON(!info))
> + return;
> +
> + list_del(&domain->auxd);
> + domain->auxd_refcnt--;
> +
> + if (!domain->auxd_refcnt && domain->default_pasid > 0)
> + intel_pasid_free_id(domain->default_pasid);

This seems unbalanced wrt to what is happening in auxiliary_link_device.
If this is necessary then it would be good to have comments saying why.
To my uniformed eye, looks like we could do this at the end of
aux_domain_remove_dev, except that we need to hold the lock.
As such perhaps it makes sense to do the pasid allocation under that
lock in the first place?

I'm not 100% sure, but is there a race if you get the final
remove running against a new add currently?

> +}
> +
> +static int aux_domain_add_dev(struct dmar_domain *domain,
> + struct device *dev)
> +{
> + int ret;
> + u8 bus, devfn;
> + unsigned long flags;
> + struct intel_iommu *iommu;
> +
> + iommu = device_to_iommu(dev, &bus, &devfn);
> + if (!iommu)
> + return -ENODEV;
> +
> + if (domain->default_pasid <= 0) {

device_domain_lock isn't held, so we might be in process of removing, see
the pasid as set, just as it becomes unset and hence leave here without
one set?

> + int pasid;
> +
> + pasid = intel_pasid_alloc_id(domain, PASID_MIN,
> + pci_max_pasids(to_pci_dev(dev)),
> + GFP_KERNEL);
> + if (pasid <= 0) {
> + pr_err("Can't allocate default pasid\n");
> + return -ENODEV;
> + }
> + domain->default_pasid = pasid;
> + }
> +
> + spin_lock_irqsave(&device_domain_lock, flags);
> + /*
> + * iommu->lock must be held to attach domain to iommu and setup the
> + * pasid entry for second level translation.
> + */
> + spin_lock(&iommu->lock);
> + ret = domain_attach_iommu(domain, iommu);
> + if (ret)
> + goto attach_failed;
> +
> + /* Setup the PASID entry for mediated devices: */
> + ret = intel_pasid_setup_second_level(iommu, domain, dev,
> + domain->default_pasid);
> + if (ret)
> + goto table_failed;
> + spin_unlock(&iommu->lock);
> +
> + auxiliary_link_device(domain, dev);
> +
> + spin_unlock_irqrestore(&device_domain_lock, flags);
> +
> + return 0;
> +
> +table_failed:
> + domain_detach_iommu(domain, iommu);
> +attach_failed:
> + spin_unlock(&iommu->lock);
> + spin_unlock_irqrestore(&device_domain_lock, flags);
> + if (!domain->auxd_refcnt && domain->default_pasid > 0)
> + intel_pasid_free_id(domain->default_pasid);

It would be odd for this to race against a remove, but in
theory it 'might' I think, potentially giving a double free.

> +
> + return ret;
> +}
> +
> +static void aux_domain_remove_dev(struct dmar_domain *domain,
> + struct device *dev)
> +{
> + struct device_domain_info *info;
> + struct intel_iommu *iommu;
> + unsigned long flags;
> +
> + if (!is_aux_domain(dev, &domain->domain))
> + return;
> +
> + spin_lock_irqsave(&device_domain_lock, flags);
> + info = dev->archdata.iommu;
> + iommu = info->iommu;
> +
> + auxiliary_unlink_device(domain, dev);
> +
> + spin_lock(&iommu->lock);
> + intel_pasid_tear_down_entry(iommu, dev, domain->default_pasid);
> + domain_detach_iommu(domain, iommu);
> + spin_unlock(&iommu->lock);
> +
> + spin_unlock_irqrestore(&device_domain_lock, flags);
> +}
> +
> static int prepare_domain_attach_device(struct iommu_domain *domain,
> struct device *dev)
> {
> @@ -5111,6 +5237,9 @@ static int intel_iommu_attach_device(struct iommu_domain *domain,
> return -EPERM;
> }
>
> + if (is_aux_domain(dev, domain))
> + return -EPERM;
> +
> /* normally dev is not mapped */
> if (unlikely(domain_context_mapped(dev))) {
> struct dmar_domain *old_domain;
> @@ -5134,12 +5263,33 @@ static int intel_iommu_attach_device(struct iommu_domain *domain,
> return domain_add_dev_info(to_dmar_domain(domain), dev);
> }
>
> +static int intel_iommu_aux_attach_device(struct iommu_domain *domain,
> + struct device *dev)
> +{
> + int ret;
> +
> + if (!is_aux_domain(dev, domain))
> + return -EPERM;
> +
> + ret = prepare_domain_attach_device(domain, dev);
> + if (ret)
> + return ret;
> +
> + return aux_domain_add_dev(to_dmar_domain(domain), dev);
> +}
> +
> static void intel_iommu_detach_device(struct iommu_domain *domain,
> struct device *dev)
> {
> dmar_remove_one_dev_info(to_dmar_domain(domain), dev);
> }
>
> +static void intel_iommu_aux_detach_device(struct iommu_domain *domain,
> + struct device *dev)
> +{
> + aux_domain_remove_dev(to_dmar_domain(domain), dev);
> +}
> +
> static int intel_iommu_map(struct iommu_domain *domain,
> unsigned long iova, phys_addr_t hpa,
> size_t size, int iommu_prot)
> @@ -5480,6 +5630,8 @@ const struct iommu_ops intel_iommu_ops = {
> .domain_free = intel_iommu_domain_free,
> .attach_dev = intel_iommu_attach_device,
> .detach_dev = intel_iommu_detach_device,
> + .aux_attach_dev = intel_iommu_aux_attach_device,
> + .aux_detach_dev = intel_iommu_aux_detach_device,
> .map = intel_iommu_map,
> .unmap = intel_iommu_unmap,
> .iova_to_phys = intel_iommu_iova_to_phys,
> diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
> index 7cf9f7f3724a..b563a61a6c39 100644
> --- a/include/linux/intel-iommu.h
> +++ b/include/linux/intel-iommu.h
> @@ -492,9 +492,11 @@ struct dmar_domain {
> /* Domain ids per IOMMU. Use u16 since
> * domain ids are 16 bit wide according
> * to VT-d spec, section 9.3 */
> + unsigned int auxd_refcnt; /* Refcount of auxiliary attaching */
>
> bool has_iotlb_device;
> struct list_head devices; /* all devices' list */
> + struct list_head auxd; /* link to device's auxiliary list */
> struct iova_domain iovad; /* iova's that belong to this domain */
>
> struct dma_pte *pgd; /* virtual address */
> @@ -513,6 +515,11 @@ struct dmar_domain {
> 2 == 1GiB, 3 == 512GiB, 4 == 1TiB */
> u64 max_addr; /* maximum mapped address */
>
> + int default_pasid; /*
> + * The default pasid used for non-SVM
> + * traffic on mediated devices.
> + */
> +
> struct iommu_domain domain; /* generic domain data structure for
> iommu core */
> };
> @@ -562,6 +569,9 @@ struct device_domain_info {
> struct list_head link; /* link to domain siblings */
> struct list_head global; /* link to global list */
> struct list_head table; /* link to pasid table */
> + struct list_head auxiliary_domains; /* auxiliary domains
> + * attached to this device
> + */
> u8 bus; /* PCI bus number */
> u8 devfn; /* PCI devfn number */
> u16 pfsid; /* SRIOV physical function source ID */


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