Re: [PATCH v5 4/8] iommu/vt-d: Aux-domain specific domain attach/detach

[Lu Baolu]

Hi,

On 1/14/19 8:26 PM, Jonathan Cameron wrote:
> On Thu, 10 Jan 2019 11:00:23 +0800
> Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx> 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@xxxxxxxxx>
> > Cc: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> > Cc: Kevin Tian <kevin.tian@xxxxxxxxx>
> > Signed-off-by: Sanjay Kumar <sanjay.k.kumar@xxxxxxxxx>
> > Signed-off-by: Liu Yi L <yi.l.liu@xxxxxxxxx>
> > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
>
> 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.

Thank you!

> > ---
> >   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?

device aux mode vs. normal mode
===============================

When we talk about the auxiliary mode (simply aux-mode), it means "the
device works in aux-mode or normal mode". "normal mode" means that the
device (and it's corresponding IOMMU) supports only RID (PCI Request ID)
based DMA translation; while, aux-mode means the the device (and it's
IOMMU) supports fine-grained DMA translation, like PASID based DMA
translation with Intel VT-d scalable mode.

We are adding below APIs to switch a device between these two modes:

int iommu_dev_enable/disable_feature(dev, IOMMU_DEV_FEAT_AUX)

And this API (still under discussion) to check which mode the device is
working in:

bool iommu_dev_has_feature(dev, IOMMU_DEV_FEAT_AUX)

aux-domain
==========

If a device is working in aux-mode and we are going to attach a domain
to this device, we say "this domain will be attached to the device in
aux mode", and simply "aux domain". So a domain is "normal" when it is
going to attach to a device in normal mode; and is "aux-domain" when it
is going to attach to a device in aux mode.

> > +{
> > +	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?

Yes. This is unbalanced.

I will move pasid free out here and it should be done with the lock
held to avoid race.

> > +}
> > +
> > +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?

Good catch, the lock should be held.

> > +		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.

Yes. Should be done with the lock held.

Best regards,
Lu Baolu

> > +
> > +	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 */