Re: [PATCH v13 3/3] iommu/vt-d: improve ITE fault handling if target device isn't valid

Dan Carpenter
2024-02-22T11:24:17Z

I'm sorry, I'm coming into this late and this is the first time I have
reviewed this patch. I see that we are at v13, and I hate to come in
with picky comments when a patch has already gone through 13
revisions...

On Thu, Feb 22, 2024 at 04:02:51AM -0500, Ethan Zhao wrote:
> Because surprise removal could happen anytime, e.g. user could request safe
> removal to EP(endpoint device) via sysfs and brings its link down to do
> surprise removal cocurrently. such aggressive cases would cause ATS
> invalidation request issued to non-existence target device, then deadly
> loop to retry that request after ITE fault triggered in interrupt context.
> this patch aims to optimize the ITE handling by checking the target device
> presence state to avoid retrying the timeout request blindly, thus avoid
> hard lockup or system hang.
>
> Devices are valid ATS invalidation request target only when they reside

"valid invalidation" is awkward wording. Can we instead say:

Devices should only be invalidated when they are in the
iommu->device_rbtree (probed, not released) and present.

> in the iommu->device_rbtre (probed, not released) and present.
^
Missing e in _rbtree.

>
> Signed-off-by: Ethan Zhao <haifeng.zhao@linux.intel.com>

This patch should have a Fixes tags and be backported to stable kernels.
I think it goes back all the way...

Fixes: 704126ad81b8 ("VT-d: handle Invalidation Queue Error to avoid system hang")

> ---
> drivers/iommu/intel/dmar.c | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
>
> diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c
> index d14797aabb7a..d01d68205557 100644
> --- a/drivers/iommu/intel/dmar.c
> +++ b/drivers/iommu/intel/dmar.c
> @@ -1273,6 +1273,9 @@ 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 device *dev = NULL;
> + struct pci_dev *pdev = NULL;
> struct q_inval *qi = iommu->qi;
> int shift = qi_shift(iommu);
>
> @@ -1317,6 +1320,13 @@ 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");
>
> @@ -1326,6 +1336,21 @@ 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 one of the
> + * current valid ATS invalidation target devices, if no, or the
> + * target device isn't presnet, don't try this request anymore.
> + * 0 value of ite_sid means old VT-d device, no ite_sid value.
> + */

This comment is kind of confusing.

/*
* If we have an ITE, then we need to check whether the sid of the ITE
* is in the rbtree (meaning it is probed and not released), and that
* the PCI device is present.
*/

My comment is slightly shorter but I think it has the necessary
information.

> + if (ite_sid) {
> + dev = device_rbtree_find(iommu, ite_sid);
> + if (!dev || !dev_is_pci(dev))
> + return -ETIMEDOUT;

-ETIMEDOUT is weird. The callers don't care which error code we return.
Change this to -ENODEV or something

> + pdev = to_pci_dev(dev);
> + if (!pci_device_is_present(pdev) &&
> + ite_sid == pci_dev_id(pci_physfn(pdev)))

The && confused me, but then I realized that probably "ite_sid ==
pci_dev_id(pci_physfn(pdev))" is always true. Can we delete that part?

pdev = to_pci_dev(dev);
if (!pci_device_is_present(pdev))
return -ENODEV;

> + return -ETIMEDOUT;

-ENODEV.

> + }
> if (qi->desc_status[wait_index] == QI_ABORT)
> return -EAGAIN;
> }

Sorry, again for nit picking a v13 patch. I'm not a domain expert but
this patchset seems reasonable to me.

regards,
dan carpenter