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

Jacob Pan
2023-05-04T22:59:17Z

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