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

From: Lu Baolu
Date: Mon Jul 06 2020 - 03:48:03 EST

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@xxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxx>
Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
Co-developed-by: Liu Yi L <yi.l.liu@xxxxxxxxx>
Signed-off-by: Liu Yi L <yi.l.liu@xxxxxxxxx>
Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
---
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