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

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Message-ID: <20240301215630.GA409512@bhelgaas>
Date: Fri, 1 Mar 2024 15:56:30 -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 Fri, Mar 01, 2024 at 09:50:36AM +0800, Ethan Zhao wrote:
> 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 ?

In PCIe spec-speak, "Set" means "assign 1 to this", and "Clear" means
"assign 0 to this".

Maybe you could copy the spec language like this:

  Invalidate all ATC entries by changing the E field in the ATS
  Capability from Clear to Set, which causes an implicit invalidation
  event.

Bjorn