Re: [PATCH v5 6/7] iommu/vt-d: Implement set_dev_pasid domain op

[Jacob Pan <jacob.jun.pan@linux.intel.com>]

Hi Baolu,

On Wed, 3 May 2023 15:26:00 +0800, Baolu Lu <baolu.lu@linux.intel.com>
wrote:

> On 4/28/23 1:49 AM, Jacob Pan wrote:
> > Devices that use ENQCMDS to submit work on buffers mapped by DMA API
> > must attach a PASID to the default domain of the device. In preparation
> > for this use case, this patch implements set_dev_pasid() for the
> > default_domain_ops.
> > 
> > If the device context has not been set up prior to this call, this will
> > set up the device context in addition to PASID attachment.
> > 
> > Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> > ---
> >   drivers/iommu/intel/iommu.c | 92 ++++++++++++++++++++++++++++++-------
> >   1 file changed, 76 insertions(+), 16 deletions(-)
> > 
> > diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> > index 388453a7415e..f9d6c31cdc8e 100644
> > --- a/drivers/iommu/intel/iommu.c
> > +++ b/drivers/iommu/intel/iommu.c
> > @@ -278,6 +278,8 @@ static LIST_HEAD(dmar_satc_units);
> >   	list_for_each_entry(rmrr, &dmar_rmrr_units, list)
> >   
> >   static void device_block_translation(struct device *dev);
> > +static void intel_iommu_detach_device_pasid(struct iommu_domain
> > *domain,
> > +					    struct device *dev,
> > ioasid_t pasid); static void intel_iommu_domain_free(struct
> > iommu_domain *domain); 
> >   int dmar_disabled = !IS_ENABLED(CONFIG_INTEL_IOMMU_DEFAULT_ON);
> > @@ -4091,8 +4093,7 @@ static void device_block_translation(struct
> > device *dev) iommu_disable_pci_caps(info);
> >   	if (!dev_is_real_dma_subdevice(dev)) {
> >   		if (sm_supported(iommu))
> > -			intel_pasid_tear_down_entry(iommu, dev,
> > -
> > IOMMU_DEF_RID_PASID, false);
> > +
> > intel_iommu_detach_device_pasid(&info->domain->domain, dev,
> > IOMMU_DEF_RID_PASID);  
> 
> device_block_translation() is called when switch RID's domain or release
> the device. I assume that we don't need to touch this path when we add
> the attach_dev_pasid support.
> 
> Blocking DMA translation through RID/PASID should be done in
> remove_dev_pasid path.
> 
> Or, I overlooked anything?
> 
> [...]
> 
> >   
> > +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.

> When the device driver starts to call attach_dev_pasid api, it means
> that the bus and device DMA configuration have been done. We could do
> the deferred default domain attaching now. So, perhaps we should add
> below code in the core:
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index f1dcfa3f1a1b..633b5ca53606 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -3296,6 +3296,12 @@ int iommu_attach_device_pasid(struct iommu_domain 
> *domain,
>          if (!group)
>                  return -ENODEV;
> 
> +       ret = iommu_deferred_attach(dev, group->default_domain);
> +       if (ret) {
> +               iommu_group_put(group);
> +               return ret;
> +       }
it will cover the device_attach, but adding a special case.

>          mutex_lock(&group->mutex);
>          curr = xa_cmpxchg(&group->pasid_array, pasid, NULL, domain, 
> GFP_KERNEL);
>          if (curr) {
> 
> Perhaps need to call iommu_deferred_attach() inside the group->mutex
> critical region?
i agree, attach RID_PASID should also be on the group's pasid_array.

> > +	 * The upper layer APIs make no assumption about the ordering
> > between
> > +	 * device attachment and the PASID attachment.
> > +	 */
> > +	ret = dmar_domain_attach_device(to_dmar_domain(domain), dev);  
> 
> Calling attach_device on the attach_dev_pasid path is not right.
I think it comes down to the philosophical differences in terms of
who is responsible for ensuring device ctx is set up  prior to device pasid
attach:
1. vt-d driver
2. upper layer API

> > +	if (ret) {
> > +		dev_err(dev, "Attach device failed\n");
> > +		return ret;
> > +	}
> > +	return dmar_domain_attach_device_pasid(dmar_domain, iommu,
> > dev, pasid); +}
> > +
> > +
> > +
> >   const struct iommu_ops intel_iommu_ops = {
> >   	.capable		= intel_iommu_capable,
> >   	.domain_alloc		= intel_iommu_domain_alloc,
> > @@ -4802,6 +4861,7 @@ const struct iommu_ops intel_iommu_ops = {
> >   #endif
> >   	.default_domain_ops = &(const struct iommu_domain_ops) {
> >   		.attach_dev		=
> > intel_iommu_attach_device,
> > +		.set_dev_pasid          =
> > intel_iommu_attach_device_pasid, .map_pages		=
> > intel_iommu_map_pages, .unmap_pages		=
> > intel_iommu_unmap_pages, .iotlb_sync_map		=
> > intel_iommu_iotlb_sync_map,  
> 
> Best regards,
> baolu


Thanks,

Jacob