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

Lu Baolu
2020-07-06T07:37:57Z

Hi Kevin,

On 2020/7/6 9:29, Tian, Kevin wrote:
>> 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...

Sure.

>
>>
>> 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.

Yes. Will remove them.

>
>> +
>> + /* 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?

Yes.

>
>> + 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;
>> + 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)"

Yes, good catch!

>
>> 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

I thought this comment explained why rcu_read_unlock() before the next
checking. In the new lookup code, we don't need to check, hence I
removed the comments.

> regarding to guest unbind, ae we preventing the fault owner (outside
> of iommu driver) to unbind against in-flight fault request?

Yes. We always wait until all prq with the same pasid completes in
gpasid_unbind().

>
>> - rcu_read_unlock();
>> -
>> - if (WARN_ON(&sdev->list == &svm->devs))
>> - sdev = NULL;
>
> similarly should we keep the WARN_ON check here?

Yes, agreed. We can keep a WARN_ON() 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
>

Best regards,
baolu