linux-kernel - Re: [PATCH 4/6] iommu: Combine device strictness requests with the global default

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Message-ID: <CAD=FV=XpYkUqGNcumJ0NvoXqbSkBaV5ZadUnpsKTMPx7tSjGig@mail.gmail.com>
Date:   Tue, 22 Jun 2021 09:53:59 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Clark <robdclark@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Saravana Kannan <saravanak@...gle.com>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux MMC List <linux-mmc@...r.kernel.org>,
        quic_c_gdjako@...cinc.com,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        linux-pci@...r.kernel.org, Joel Fernandes <joel@...lfernandes.org>,
        Rajat Jain <rajatja@...gle.com>,
        Sonny Rao <sonnyrao@...omium.org>,
        Veerabhadrarao Badiganti <vbadigan@...eaurora.org>
Subject: Re: [PATCH 4/6] iommu: Combine device strictness requests with the
 global default

Hi,

On Mon, Jun 21, 2021 at 7:05 PM Lu Baolu <baolu.lu@...ux.intel.com> wrote:
>
> On 6/22/21 7:52 AM, Douglas Anderson wrote:
> > @@ -1519,7 +1542,8 @@ static int iommu_get_def_domain_type(struct device *dev)
> >
> >   static int iommu_group_alloc_default_domain(struct bus_type *bus,
> >                                           struct iommu_group *group,
> > -                                         unsigned int type)
> > +                                         unsigned int type,
> > +                                         struct device *dev)
> >   {
> >       struct iommu_domain *dom;
> >
> > @@ -1534,6 +1558,12 @@ static int iommu_group_alloc_default_domain(struct bus_type *bus,
> >       if (!dom)
> >               return -ENOMEM;
> >
> > +     /* Save the strictness requests from the device */
> > +     if (dev && type == IOMMU_DOMAIN_DMA) {
> > +             dom->request_non_strict = dev->request_non_strict_iommu;
> > +             dom->force_strict = dev->force_strict_iommu;
> > +     }
> > +
>
> An iommu default domain might be used by multiple devices which might
> have different "strict" attributions. Then who could override who?

My gut instinct would be that if multiple devices were part of a given
domain that it would be combined like this:

1. Any device that requests strict makes the domain strict force strict.

2. To request non-strict all of the devices in the domain would have
to request non-strict.

To do that I'd have to change my patchset obviously, but I don't think
it should be hard. We can just keep a count of devices and a count of
the strict vs. non-strict requests? If there are no other blockers
I'll try to do that in my v2.

-Doug