Re: [PATCH v2 15/19] iommu/vt-d: Add bind guest PASID support

Auger Eric
2019-04-30T07:05:13Z

On 4/29/19 5:25 PM, Jacob Pan wrote:
> On Fri, 26 Apr 2019 18:15:27 +0200
> Auger Eric <eric.auger@redhat.com> wrote:
>
>> Hi Jacob,
>>
>> On 4/24/19 1:31 AM, Jacob Pan wrote:
>>> When supporting guest SVA with emulated IOMMU, the guest PASID
>>> table is shadowed in VMM. Updates to guest vIOMMU PASID table
>>> will result in PASID cache flush which will be passed down to
>>> the host as bind guest PASID calls.
>>>
>>> For the SL page tables, it will be harvested from device's
>>> default domain (request w/o PASID), or aux domain in case of
>>> mediated device.
>>>
>>> .-------------. .---------------------------.
>>> | vIOMMU | | Guest process CR3, FL only|
>>> | | '---------------------------'
>>> .----------------/
>>> | PASID Entry |--- PASID cache flush -
>>> '-------------' |
>>> | | V
>>> | | CR3 in GPA
>>> '-------------'
>>> Guest
>>> ------| Shadow |--------------------------|--------
>>> v v v
>>> Host
>>> .-------------. .----------------------.
>>> | pIOMMU | | Bind FL for GVA-GPA |
>>> | | '----------------------'
>>> .----------------/ |
>>> | PASID Entry | V (Nested xlate)
>>> '----------------\.------------------------------.
>>> | | |SL for GPA-HPA, default domain|
>>> | | '------------------------------'
>>> '-------------'
>>> Where:
>>> - FL = First level/stage one page tables
>>> - SL = Second level/stage two page tables
>>>
>>> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
>>> Signed-off-by: Liu, Yi L <yi.l.liu@linux.intel.com>
>>> ---
>>> drivers/iommu/intel-iommu.c | 4 +
>>> drivers/iommu/intel-svm.c | 174
>>> ++++++++++++++++++++++++++++++++++++++++++++
>>> include/linux/intel-iommu.h | 10 ++- include/linux/intel-svm.h
>>> | 7 ++ 4 files changed, 193 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/iommu/intel-iommu.c
>>> b/drivers/iommu/intel-iommu.c index 77bbe1b..89989b5 100644
>>> --- a/drivers/iommu/intel-iommu.c
>>> +++ b/drivers/iommu/intel-iommu.c
>>> @@ -5768,6 +5768,10 @@ const struct iommu_ops intel_iommu_ops = {
>>> .dev_enable_feat = intel_iommu_dev_enable_feat,
>>> .dev_disable_feat = intel_iommu_dev_disable_feat,
>>> .pgsize_bitmap = INTEL_IOMMU_PGSIZES,
>>> +#ifdef CONFIG_INTEL_IOMMU_SVM
>>> + .sva_bind_gpasid = intel_svm_bind_gpasid,
>>> + .sva_unbind_gpasid = intel_svm_unbind_gpasid,
>>> +#endif
>>> };
>>>
>>> static void quirk_iommu_g4x_gfx(struct pci_dev *dev)
>>> diff --git a/drivers/iommu/intel-svm.c b/drivers/iommu/intel-svm.c
>>> index 8fff212..0a973c2 100644
>>> --- a/drivers/iommu/intel-svm.c
>>> +++ b/drivers/iommu/intel-svm.c
>>> @@ -227,6 +227,180 @@ static const struct mmu_notifier_ops
>>> intel_mmuops = {
>>> static DEFINE_MUTEX(pasid_mutex);
>>> static LIST_HEAD(global_svm_list);
>>> +#define for_each_svm_dev() \
>>> + list_for_each_entry(sdev, &svm->devs, list) \
>>> + if (dev == sdev->dev) \
>>> +
>>> +int intel_svm_bind_gpasid(struct iommu_domain *domain,
>>> + struct device *dev,
>>> + struct gpasid_bind_data *data)
>>> +{
>>> + struct intel_iommu *iommu = intel_svm_device_to_iommu(dev);
>>> + struct intel_svm_dev *sdev;
>>> + struct intel_svm *svm = NULL;
>>> + struct dmar_domain *ddomain;
>>> + int pasid_max;
>>> + int ret = 0;
>>> +
>>> + if (WARN_ON(!iommu) || !data)
>>> + return -EINVAL;
>>> +
>>> + if (dev_is_pci(dev)) {
>>> + pasid_max = pci_max_pasids(to_pci_dev(dev));
>>> + if (pasid_max < 0)
>>> + return -EINVAL;
>>> + } else
>>> + pasid_max = 1 << 20;
>>> +
>>> + if (data->pasid <= 0 || data->pasid >= pasid_max)
>>> + return -EINVAL;
>>> +
>>> + ddomain = to_dmar_domain(domain);
>>> + /* REVISIT:
>>> + * Sanity check adddress width and paging mode support
>>> + * width matching in two dimensions:
>>> + * 1. paging mode CPU <= IOMMU
>>> + * 2. address width Guest <= Host.
>>> + */
>>> + mutex_lock(&pasid_mutex);
>>> + svm = ioasid_find(NULL, data->pasid, NULL);
>>> + if (IS_ERR(svm)) {
>>> + ret = PTR_ERR(svm);
>>> + goto out;
>>> + }
>>> + if (svm) {
>>> + if (list_empty(&svm->devs)) {
>>> + dev_err(dev, "GPASID %d has no devices
>>> bond but SVA is allocated\n",
>>> + data->pasid);
>>> + ret = -ENODEV; /*
>>> + * If we found svm for the
>>> PASID, there must be at
>>> + * least one device bond,
>>> otherwise svm should be freed.
>>> + */
>> comment should be put after list_empty I think. In which circumstances
>> can it happen, I mean, isn't it a BUG_ON case?
> Well, I think failing to bind guest PASID is not severe enough to the
> host to use BUG_ON. It has to be something more catastrophic to use
> BUG_ON right? I will relocate the comments.
When the error is due to a programming error at kernel error (not
induced by any userspace call) I guess it is acceptable to put a BUG_ON.
However the usage of BUG_ON() is generally frown upon so my question
rather was to understand if this can really happen and why?
>>> + goto out;
>>> + }
>>> + for_each_svm_dev() {
>>> + /* In case of multiple sub-devices of the
>>> same pdev assigned, we should
>>> + * allow multiple bind calls with the same
>>> PASID and pdev.
>>> + */
>>> + sdev->users++;
>>> + goto out;
>>> + }
>>> + } else {
>>> + /* We come here when PASID has never been bond to
>>> a device. */
>>> + svm = kzalloc(sizeof(*svm), GFP_KERNEL);
>>> + if (!svm) {
>>> + ret = -ENOMEM;
>>> + goto out;
>>> + }
>>> + /* REVISIT: upper layer/VFIO can track host
>>> process that bind the PASID.
>>> + * ioasid_set = mm might be sufficient for vfio to
>>> check pasid VMM
>>> + * ownership.
>>> + */
>>> + svm->mm = get_task_mm(current);
>>> + svm->pasid = data->pasid;
>>> + refcount_set(&svm->refs, 0);
>>> + ioasid_set_data(data->pasid, svm);
>>> + INIT_LIST_HEAD_RCU(&svm->devs);
>>> + INIT_LIST_HEAD(&svm->list);
>>> +
>>> + mmput(svm->mm);
>>> + }
>>> + svm->flags |= SVM_FLAG_GUEST_MODE;
>>> + sdev = kzalloc(sizeof(*sdev), GFP_KERNEL);
>>> + if (!sdev) {
>>> + ret = -ENOMEM;
>> in case of failure what is the state of svm (you added the
>> SVM_FLAG_GUEST_MODE bit typically, is it safe to leave it?)
> The SVM_FLAG_GUEST_MODE flag is used for fault reporting where faults
> such as PRQ need to be injected into the guest. If this kzalloc()
> fails, the nested translation would not be setup for this PASID. So
> there shouldn't be any user of the flag. But I think it is better to
> move svm->flags |= SVM_FLAG_GUEST_MODE; to the end when everything is
> setup for nesting.
ok
>
>>> + goto out;
>>> + }
>>> + sdev->dev = dev;
>>> + sdev->users = 1;
>>> +
>>> + /* Set up device context entry for PASID if not enabled
>>> already */
>>> + ret = intel_iommu_enable_pasid(iommu, sdev->dev);
>>> + if (ret) {
>>> + dev_err(dev, "Failed to enable PASID
>>> capability\n");
>>> + kfree(sdev);
>> same here
>>> + goto out;
>>> + }
>>> +
>>> + /*
>>> + * For guest bind, we need to set up PASID table entry as
>>> follows:
>>> + * - FLPM matches guest paging mode
>>> + * - turn on nested mode
>>> + * - SL guest address width matching
>>> + */
>>> + ret = intel_pasid_setup_nested(iommu,
>>> + dev,
>>> + (pgd_t *)data->gcr3,
>>> + data->pasid,
>>> + data->flags,
>>> + ddomain,
>>> + data->addr_width);
>>> + if (ret) {
>>> + dev_err(dev, "Failed to set up PASID %d in nested
>>> mode, Err %d\n",
>>> + data->pasid, ret);
>>> + kfree(sdev);
>>> + goto out;
>>> + }
>>> +
>>> + init_rcu_head(&sdev->rcu);
>>> + refcount_inc(&svm->refs);
>>> + list_add_rcu(&sdev->list, &svm->devs);
>>> + out:
>>> + mutex_unlock(&pasid_mutex);
>>> + return ret;
>>> +}
>>> +
>>> +int intel_svm_unbind_gpasid(struct device *dev, int pasid)
>>> +{
>>> + struct intel_svm_dev *sdev;
>>> + struct intel_iommu *iommu;
>>> + struct intel_svm *svm;
>>> + int ret = -EINVAL;
>>> +
>>> + mutex_lock(&pasid_mutex);
>>> + iommu = intel_svm_device_to_iommu(dev);
>>> + if (!iommu)
>>> + goto out;
>>> +
>>> + svm = ioasid_find(NULL, pasid, NULL);
>>> + if (IS_ERR(svm)) {
>>> + ret = PTR_ERR(svm);
>>> + goto out;
>>> + }
>>> +
>>> + if (!svm)
>>> + goto out;
>>> +
>>> + for_each_svm_dev() {
>>> + ret = 0;
>>> + sdev->users--;
>>> + if (!sdev->users) {
>>> + list_del_rcu(&sdev->list);
>>> + intel_pasid_tear_down_entry(iommu, dev,
>>> svm->pasid);
>>> + /* TODO: Drain in flight PRQ for the PASID
>>> since it
>>> + * may get reused soon, we don't want to
>>> + * confuse with its previous live.
>>> + * intel_svm_drain_prq(dev, pasid);
>>> + */
>>> + kfree_rcu(sdev, rcu);
>>> +
>>> + if (list_empty(&svm->devs)) {
>>> + list_del(&svm->list);
>>> + kfree(svm);
>>> + /*
>>> + * We do not free PASID here until
>>> explicit call
>>> + * from the guest to free.
>> can you be confident in the guest?
> No. But I have confident in the kernel VFIO code to manage guest life
> cycle :)
> I assume when a guest doesn't do unbind when it dies or unload a
> assigned device, I expect VFIO to free all the PASIDs. VFIO needs to
> police the PASID ownership anyway in order to make sure a PASID
> assigned to guest A cannot be used to bind from guest B.
> This is the flow I worked out with Yi, who is doing the VFIO part. Any
> particular concerns?
No I just wanted to make sure someone is going to take care of the final
tear down even if the userspace fails to do things as expected. Maybe
adding a comment to explain who has the ownership of the final tear down
would help here.

Thanks

Eric
>
>>> + */
>>> + ioasid_set_data(pasid, NULL);
>>> + }
>>> + }
>>> + break;
>>> + }
>>> + out:
>>> + mutex_unlock(&pasid_mutex);
>>> +
>>> + return ret;
>>> +}
>>>
>>> int intel_svm_bind_mm(struct device *dev, int *pasid, int flags,
>>> struct svm_dev_ops *ops) {
>>> diff --git a/include/linux/intel-iommu.h
>>> b/include/linux/intel-iommu.h index 48fa164..5d67d0d4 100644
>>> --- a/include/linux/intel-iommu.h
>>> +++ b/include/linux/intel-iommu.h
>>> @@ -677,7 +677,9 @@ int intel_iommu_enable_pasid(struct intel_iommu
>>> *iommu, struct device *dev); int intel_svm_init(struct intel_iommu
>>> *iommu); extern int intel_svm_enable_prq(struct intel_iommu *iommu);
>>> extern int intel_svm_finish_prq(struct intel_iommu *iommu);
>>> -
>>> +extern int intel_svm_bind_gpasid(struct iommu_domain *domain,
>>> + struct device *dev, struct gpasid_bind_data *data);
>>> +extern int intel_svm_unbind_gpasid(struct device *dev, int pasid);
>>> struct svm_dev_ops;
>>>
>>> struct intel_svm_dev {
>>> @@ -693,12 +695,16 @@ struct intel_svm_dev {
>>>
>>> struct intel_svm {
>>> struct mmu_notifier notifier;
>>> - struct mm_struct *mm;
>>> + union {
>>> + struct mm_struct *mm;
>>> + u64 gcr3;
>>> + };
>>> struct intel_iommu *iommu;
>>> int flags;
>>> int pasid;
>>> struct list_head devs;
>>> struct list_head list;
>>> + refcount_t refs; /* # of devs bond to the PASID */
>> number of devices sharing the same PASID?
> more clear wording, thanks.
>>> };
>>>
>>> extern struct intel_iommu *intel_svm_device_to_iommu(struct device
>>> *dev); diff --git a/include/linux/intel-svm.h
>>> b/include/linux/intel-svm.h index e3f7631..34b0a3b 100644
>>> --- a/include/linux/intel-svm.h
>>> +++ b/include/linux/intel-svm.h
>>> @@ -52,6 +52,13 @@ struct svm_dev_ops {
>>> * do such IOTLB flushes automatically.
>>> */
>>> #define SVM_FLAG_SUPERVISOR_MODE (1<<1)
>>> +/*
>>> + * The SVM_FLAG_GUEST_MODE flag is used when a guest process bind
>>> to a device.
>> binds
> will fix
>
>>> + * In this case the mm_struct is in the guest kernel or userspace,
>>> its life
>>> + * cycle is managed by VMM and VFIO layer. For IOMMU driver, this
>>> API provides
>>> + * means to bind/unbind guest CR3 with PASIDs allocated for a
>>> device.
>>> + */
>>> +#define SVM_FLAG_GUEST_MODE (1<<2)
>>>
>>> #ifdef CONFIG_INTEL_IOMMU_SVM
>>>
>>>
>>
>> Thanks
>>
>> Eric
>
> [Jacob Pan]
>