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

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Message-ID: <20240229210640.GA362869@bhelgaas>
Date: Thu, 29 Feb 2024 15:06:40 -0600
From: Bjorn Helgaas <helgaas@...nel.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,
	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 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)

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

> 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.

> +		 */
> +		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
>