Re: [PATCH v2 3/4] iommu/vt-d: Report page request faults for guest SVA

Lu Baolu
2020-07-06T07:48:05Z

On 2020/7/6 9:36, Tian, Kevin wrote:
>> From: Tian, Kevin
>> Sent: Monday, July 6, 2020 9:30 AM
>>
>>> From: Lu Baolu <baolu.lu@linux.intel.com>
>>> Sent: Monday, July 6, 2020 8:26 AM
>>>
>>> A pasid might be bound to a page table from a VM guest via the iommu
>>> ops.sva_bind_gpasid. In this case, when a DMA page fault is detected
>>> on the physical IOMMU, we need to inject the page fault request into
>>> the guest. After the guest completes handling the page fault, a page
>>> response need to be sent back via the iommu ops.page_response().
>>>
>>> This adds support to report a page request fault. Any external module
>>> which is interested in handling this fault should regiester a notifier
>>> callback.
>>
>> be specific on which notifier to be registered...
>>
>>>
>>> Co-developed-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
>>> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
>>> Co-developed-by: Liu Yi L <yi.l.liu@intel.com>
>>> Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
>>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>>> ---
>>> drivers/iommu/intel/svm.c | 99 ++++++++++++++++++++++++++++++++-----
>> --
>>> 1 file changed, 81 insertions(+), 18 deletions(-)
>>>
>>> diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
>>> index c23167877b2b..08c58c2b1a06 100644
>>> --- a/drivers/iommu/intel/svm.c
>>> +++ b/drivers/iommu/intel/svm.c
>>> @@ -815,6 +815,57 @@ static void intel_svm_drain_prq(struct device *dev,
>>> int pasid)
>>> }
>>> }
>>>
>>> +static int prq_to_iommu_prot(struct page_req_dsc *req)
>>> +{
>>> + int prot = 0;
>>> +
>>> + if (req->rd_req)
>>> + prot |= IOMMU_FAULT_PERM_READ;
>>> + if (req->wr_req)
>>> + prot |= IOMMU_FAULT_PERM_WRITE;
>>> + if (req->exe_req)
>>> + prot |= IOMMU_FAULT_PERM_EXEC;
>>> + if (req->pm_req)
>>> + prot |= IOMMU_FAULT_PERM_PRIV;
>>> +
>>> + return prot;
>>> +}
>>> +
>>> +static int
>>> +intel_svm_prq_report(struct device *dev, struct page_req_dsc *desc)
>>> +{
>>> + struct iommu_fault_event event;
>>> + u8 bus, devfn;
>>> +
>>> + memset(&event, 0, sizeof(struct iommu_fault_event));
>>> + bus = PCI_BUS_NUM(desc->rid);
>>> + devfn = desc->rid & 0xff;
>>
>> not required.
>>
>>> +
>>> + /* Fill in event data for device specific processing */
>>> + event.fault.type = IOMMU_FAULT_PAGE_REQ;
>>> + event.fault.prm.addr = desc->addr;
>>> + event.fault.prm.pasid = desc->pasid;
>>> + event.fault.prm.grpid = desc->prg_index;
>>> + event.fault.prm.perm = prq_to_iommu_prot(desc);
>>> +
>>> + /*
>>> + * Set last page in group bit if private data is present,
>>> + * page response is required as it does for LPIG.
>>> + */
>>
>> move to priv_data_present check?
>>
>>> + if (desc->lpig)
>>> + event.fault.prm.flags |=
>>> IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE;
>>> + if (desc->pasid_present)
>>> + event.fault.prm.flags |=
>>> IOMMU_FAULT_PAGE_REQUEST_PASID_VALID;
>>> + if (desc->priv_data_present) {
>>> + event.fault.prm.flags |=
>>> IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE;
>
> btw earlier comment is more about the behavior of the fault
> handler (e.g. the guest), but not about why we need convert
> to last_page prm flag. Let's make it clear that doing so is
> because iommu_report_device_fault doesn't understand this
> vt-d specific requirement thus we set last_page as a workaround.

Yes. I will add this in the comment.

Best regards,
baolu

>
> Thanks
> Kevin
>
>>> + event.fault.prm.flags |=
>>> IOMMU_FAULT_PAGE_REQUEST_PRIV_DATA;
>>> + memcpy(event.fault.prm.private_data, desc->priv_data,
>>> + sizeof(desc->priv_data));
>>> + }
>>> +
>>> + return iommu_report_device_fault(dev, &event);
>>> +}
>>> +
>>> static irqreturn_t prq_event_thread(int irq, void *d)
>>> {
>>> struct intel_iommu *iommu = d;
>>> @@ -828,7 +879,7 @@ static irqreturn_t prq_event_thread(int irq, void *d)
>>> tail = dmar_readq(iommu->reg + DMAR_PQT_REG) &
>>> PRQ_RING_MASK;
>>> head = dmar_readq(iommu->reg + DMAR_PQH_REG) &
>>> PRQ_RING_MASK;
>>> while (head != tail) {
>>> - struct intel_svm_dev *sdev;
>>> + struct intel_svm_dev *sdev = NULL;
>>
>> move to outside of the loop, otherwise later check always hit "if (!sdev)"
>>
>>> struct vm_area_struct *vma;
>>> struct page_req_dsc *req;
>>> struct qi_desc resp;
>>> @@ -864,6 +915,20 @@ static irqreturn_t prq_event_thread(int irq, void
>> *d)
>>> }
>>> }
>>>
>>> + if (!sdev || sdev->sid != req->rid) {
>>> + struct intel_svm_dev *t;
>>> +
>>> + sdev = NULL;
>>> + rcu_read_lock();
>>> + list_for_each_entry_rcu(t, &svm->devs, list) {
>>> + if (t->sid == req->rid) {
>>> + sdev = t;
>>> + break;
>>> + }
>>> + }
>>> + rcu_read_unlock();
>>> + }
>>> +
>>> result = QI_RESP_INVALID;
>>> /* Since we're using init_mm.pgd directly, we should never
>>> take
>>> * any faults on kernel addresses. */
>>> @@ -874,6 +939,17 @@ static irqreturn_t prq_event_thread(int irq, void
>> *d)
>>> if (!is_canonical_address(address))
>>> goto bad_req;
>>>
>>> + /*
>>> + * If prq is to be handled outside iommu driver via receiver of
>>> + * the fault notifiers, we skip the page response here.
>>> + */
>>> + if (svm->flags & SVM_FLAG_GUEST_MODE) {
>>> + if (sdev && !intel_svm_prq_report(sdev->dev, req))
>>> + goto prq_advance;
>>> + else
>>> + goto bad_req;
>>> + }
>>> +
>>> /* If the mm is already defunct, don't handle faults. */
>>> if (!mmget_not_zero(svm->mm))
>>> goto bad_req;
>>> @@ -892,24 +968,10 @@ static irqreturn_t prq_event_thread(int irq, void
>> *d)
>>> goto invalid;
>>>
>>> result = QI_RESP_SUCCESS;
>>> - invalid:
>>> +invalid:
>>> mmap_read_unlock(svm->mm);
>>> mmput(svm->mm);
>>> - bad_req:
>>> - /* Accounting for major/minor faults? */
>>> - rcu_read_lock();
>>> - list_for_each_entry_rcu(sdev, &svm->devs, list) {
>>> - if (sdev->sid == req->rid)
>>> - break;
>>> - }
>>> - /* Other devices can go away, but the drivers are not
>>> permitted
>>> - * to unbind while any page faults might be in flight. So it's
>>> - * OK to drop the 'lock' here now we have it. */
>>
>> should we keep and move this comment to earlier sdev lookup? and
>> regarding to guest unbind, ae we preventing the fault owner (outside
>> of iommu driver) to unbind against in-flight fault request?
>>
>>> - rcu_read_unlock();
>>> -
>>> - if (WARN_ON(&sdev->list == &svm->devs))
>>> - sdev = NULL;
>>
>> similarly should we keep the WARN_ON check here?
>>
>>> -
>>> +bad_req:
>>> if (sdev && sdev->ops && sdev->ops->fault_cb) {
>>> int rwxp = (req->rd_req << 3) | (req->wr_req << 2) |
>>> (req->exe_req << 1) | (req->pm_req);
>>> @@ -920,7 +982,7 @@ static irqreturn_t prq_event_thread(int irq, void *d)
>>> and these can be NULL. Do not use them below this point!
>>> */
>>> sdev = NULL;
>>> svm = NULL;
>>> - no_pasid:
>>> +no_pasid:
>>> if (req->lpig || req->priv_data_present) {
>>> /*
>>> * Per VT-d spec. v3.0 ch7.7, system software must
>>> @@ -945,6 +1007,7 @@ static irqreturn_t prq_event_thread(int irq, void
>> *d)
>>> resp.qw3 = 0;
>>> qi_submit_sync(iommu, &resp, 1, 0);
>>> }
>>> +prq_advance:
>>> head = (head + sizeof(*req)) & PRQ_RING_MASK;
>>> }
>>>
>>> --
>>> 2.17.1
>>
>> Thanks
>> Kevin