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

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Message-ID: <c655cd15-c883-483b-b698-b1b7ae360388@moroto.mountain>
Date: Thu, 22 Feb 2024 14:24:11 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Ethan Zhao <haifeng.zhao@...ux.intel.com>
Cc: baolu.lu@...ux.intel.com, bhelgaas@...gle.com, robin.murphy@....com,
	jgg@...pe.ca, kevin.tian@...el.com, dwmw2@...radead.org,
	will@...nel.org, lukas@...ner.de, yi.l.liu@...el.com,
	iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH v13 3/3] iommu/vt-d: improve ITE fault handling if target
 device isn't valid

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@...ux.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