Re: [PATCH v12 5/5] iommu/vt-d: improve ITE fault handling if target device isn't present

Baolu Lu
2024-02-15T07:43:33Z

On 2/2/24 3:34 AM, Jason Gunthorpe wrote:
> On Wed, Jan 31, 2024 at 02:21:20PM +0800, Baolu Lu wrote:
>> An rbtree for IOMMU device data for the VT-d driver would be beneficial.
>> It also benefits other paths of fault handling, such as the I/O page
>> fault handling path, where it currently still relies on the PCI
>> subsystem to convert a RID value into a pci_device structure.
>>
>> Given that such an rbtree would be helpful for multiple individual
>> drivers that handle PCI devices, it seems valuable to implement it in
>> the core?
> rbtree is already supposed to be a re-usable library.
>
> There is already good helper support in rbtree to make things easy to
> implement. I see arm hasn't used them yet, it should look something
> like this:

I have posted a similar implementation for the vt-d driver here:

https://lore.kernel.org/linux-iommu/20240215072249.4465-1-baolu.lu@linux.intel.com/

Based on this implementation, only patches 1 and 2 are required. The
last patch could be like below (code compiled but not tested, comments
not changed yet):

diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c
index f9b63c2875f7..30a659a4d3ed 100644
--- a/drivers/iommu/intel/dmar.c
+++ b/drivers/iommu/intel/dmar.c
@@ -1272,6 +1272,7 @@ static int qi_check_fault(struct intel_iommu
*iommu, int index, int wait_index)
{
u32 fault;
int head, tail;
+ u64 iqe_err, ite_sid;
struct q_inval *qi = iommu->qi;
int shift = qi_shift(iommu);

@@ -1316,6 +1317,13 @@ static int qi_check_fault(struct intel_iommu
*iommu, int index, int wait_index)
tail = readl(iommu->reg + DMAR_IQT_REG);
tail = ((tail >> shift) - 1 + QI_LENGTH) % QI_LENGTH;

+ /*
+ * SID field is valid only when the ITE field is Set in
FSTS_REG
+ * see Intel VT-d spec r4.1, section 11.4.9.9
+ */
+ iqe_err = dmar_readq(iommu->reg + DMAR_IQER_REG);
+ ite_sid = DMAR_IQER_REG_ITESID(iqe_err);
+
writel(DMA_FSTS_ITE, iommu->reg + DMAR_FSTS_REG);
pr_info("Invalidation Time-out Error (ITE) cleared\n");

@@ -1325,6 +1333,19 @@ static int qi_check_fault(struct intel_iommu
*iommu, int index, int wait_index)
head = (head - 2 + QI_LENGTH) % QI_LENGTH;
} while (head != tail);

+ /*
+ * If got ITE, we need to check if the sid of ITE is the
same as
+ * current ATS invalidation target device, if yes, don't
try this
+ * request anymore if the target device isn't present.
+ * 0 value of ite_sid means old VT-d device, no ite_sid
value.
+ */
+ if (ite_sid) {
+ struct device *dev = device_rbtree_find(iommu,
ite_sid);
+
+ if (!dev || !pci_device_is_present(to_pci_dev(dev)))
+ return -ETIMEDOUT;
+ }
+
if (qi->desc_status[wait_index] == QI_ABORT)
return -EAGAIN;
}

Best regards,
baolu