linux-kernel - Re: [PATCH] iommu/vt-d: avoid sending explicit ATS invalidation request to released device

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Date: Fri, 1 Mar 2024 09:50:36 +0800
From: Ethan Zhao <haifeng.zhao@...ux.intel.com>
To: Bjorn Helgaas <helgaas@...nel.org>
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, dan.carpenter@...aro.org,
 iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/vt-d: avoid sending explicit ATS invalidation
 request to released device


On 3/1/2024 5:06 AM, Bjorn Helgaas wrote:
> On Wed, Feb 28, 2024 at 10:31:38PM -0500, Ethan Zhao wrote:
>> The introduction of per iommu device rbtree also defines the lifetime of
>> interoperation between iommu and devices, if the device has been released
>> from device rbtree, no need to send ATS invalidation request to it anymore,
>> thus avoid the possibility of later ITE fault to be triggered.
>>
>> This is part of the followup of prior proposed patchset
>>
>> https://do-db2.lkml.org/lkml/2024/2/22/350
> Please use https://lore.kernel.org/ URLs instead.  This one looks like
> https://lore.kernel.org/r/20240222090251.2849702-1-haifeng.zhao@linux.intel.com/
>
>> To make sure all the devTLB entries to be invalidated in the device release
>> path, do implict invalidation by fapping the E bit of ATS control register.
>> see PCIe spec v6.2, sec 10.3.7 implicit invalidation events.
> s/implict/implicit/
>
> s/fapping/?/  (no idea :)  "flipping"?  Oh, probably "flapping" per the
> comment below.  But I think "flapping" is ambiguous; "setting" would be
> better)

Yup, like the memory bit flipping, no idea what is the right word,
setting one bit to 0, then 1, then back to 0. perhaps details the
setting action 0-->1-->0 ?

> s/v6.2/r6.2/ (also below in comment)

got it.

>
>> Fixes: 6f7db75e1c46 ("iommu/vt-d: Add second level page table interface")
>> Signed-off-by: Ethan Zhao <haifeng.zhao@...ux.intel.com>
>> ---
>>   drivers/iommu/intel/iommu.c | 6 ++++++
>>   drivers/iommu/intel/pasid.c | 7 +++++++
>>   2 files changed, 13 insertions(+)
>>
>> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
>> index 6743fe6c7a36..b85d88ccb4b0 100644
>> --- a/drivers/iommu/intel/iommu.c
>> +++ b/drivers/iommu/intel/iommu.c
>> @@ -1368,6 +1368,12 @@ static void iommu_disable_pci_caps(struct device_domain_info *info)
>>   	pdev = to_pci_dev(info->dev);
>>   
>>   	if (info->ats_enabled) {
>> +		pci_disable_ats(pdev);
>> +		/*
>> +		 * flap the E bit of ATS control register to do implicit
>> +		 * ATS invlidation, see PCIe spec v6.2, sec 10.3.7
> s/invlidation/invalidation/
>
> I would put the comment above the pci_disable_ats(), so it looks like
> this:
>
>    /* comment ... */
>    pci_disable_ats(pdev);
>    pci_enable_ats(pdev, VTD_PAGE_SHIFT);
>
>    pci_disable_ats(pdev);
>
> because the spec says the E field must change from Clear to Set to
> cause invalidation of all ATC entries, so it's important to see that
> we clear E first, then set it.

Great, will correct.

Thanks,
Ethan

>
>> +		 */
>> +		pci_enable_ats(pdev, VTD_PAGE_SHIFT);
>>   		pci_disable_ats(pdev);
>>   		info->ats_enabled = 0;
>>   		domain_update_iotlb(info->domain);
>> diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
>> index 108158e2b907..5f13e017a12c 100644
>> --- a/drivers/iommu/intel/pasid.c
>> +++ b/drivers/iommu/intel/pasid.c
>> @@ -215,6 +215,13 @@ devtlb_invalidation_with_pasid(struct intel_iommu *iommu,
>>   		return;
>>   
>>   	sid = info->bus << 8 | info->devfn;
>> +	/*
>> +	 * If device has been released from rbtree, no need to send ATS
>> +	 * Invalidation	request anymore, that could cause ITE fault.
>> +	 */
>> +	if (!device_rbtree_find(iommu, sid))
>> +		return;
>> +
>>   	qdep = info->ats_qdep;
>>   	pfsid = info->pfsid;
>>   
>> -- 
>> 2.31.1
>>