linux-kernel - Re: [PATCH v2 3/7] PCI/ACS: Enable PCI_ACS_TB for untrusted/external-facing devices

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Date:   Mon, 6 Jul 2020 16:12:31 -0700
From:   Rajat Jain <rajatja@...gle.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        "open list:AMD IOMMU (AMD-VI)" <iommu@...ts.linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Raj Ashok <ashok.raj@...el.com>,
        "Krishnakumar, Lalithambika" <lalithambika.krishnakumar@...el.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Prashant Malani <pmalani@...gle.com>,
        Benson Leung <bleung@...gle.com>,
        Todd Broch <tbroch@...gle.com>,
        Alex Levin <levinale@...gle.com>,
        Mattias Nissler <mnissler@...gle.com>,
        Rajat Jain <rajatxjain@...il.com>,
        Bernie Keany <bernie.keany@...el.com>,
        Aaron Durbin <adurbin@...gle.com>,
        Diego Rivas <diegorivas@...gle.com>,
        Duncan Laurie <dlaurie@...gle.com>,
        Furquan Shaikh <furquan@...gle.com>,
        Jesse Barnes <jsbarnes@...gle.com>,
        Christian Kellner <christian@...lner.me>,
        Alex Williamson <alex.williamson@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Oliver O'Halloran" <oohall@...il.com>,
        Saravana Kannan <saravanak@...gle.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Subject: Re: [PATCH v2 3/7] PCI/ACS: Enable PCI_ACS_TB for untrusted/external-facing
 devices

On Mon, Jul 6, 2020 at 9:45 AM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Mon, Jun 29, 2020 at 09:49:39PM -0700, Rajat Jain wrote:
> > When enabling ACS, enable translation blocking for external facing ports
> > and untrusted devices.
> >
> > Signed-off-by: Rajat Jain <rajatja@...gle.com>
> > ---
> > v2: Commit log change
> >
> >  drivers/pci/pci.c    |  4 ++++
> >  drivers/pci/quirks.c | 11 +++++++++++
> >  2 files changed, 15 insertions(+)
> >
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index d2ff987585855..79853b52658a2 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -3330,6 +3330,10 @@ static void pci_std_enable_acs(struct pci_dev *dev)
> >       /* Upstream Forwarding */
> >       ctrl |= (cap & PCI_ACS_UF);
> >
> > +     if (dev->external_facing || dev->untrusted)
> > +             /* Translation Blocking */
> > +             ctrl |= (cap & PCI_ACS_TB);
> > +
> >       pci_write_config_word(dev, pos + PCI_ACS_CTRL, ctrl);
> >  }
> >
> > diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> > index b341628e47527..6294adeac4049 100644
> > --- a/drivers/pci/quirks.c
> > +++ b/drivers/pci/quirks.c
> > @@ -4934,6 +4934,13 @@ static void pci_quirk_enable_intel_rp_mpc_acs(struct pci_dev *dev)
> >       }
> >  }
> >
> > +/*
> > + * Currently this quirk does the equivalent of
> > + * PCI_ACS_RR | PCI_ACS_CR | PCI_ACS_UF | PCI_ACS_SV
> > + *
> > + * Currently missing, it also needs to do equivalent of PCI_ACS_TB,
> > + * if dev->external_facing || dev->untrusted
>
> I don't understand this comment.  Is this a "TODO"?  Is there
> something more that needs to be done here?

Yes. I'll mark it as a TODO to make it more clear.

>
> After a patch is applied, a comment should describe the code as it is.
>
> > + */
> >  static int pci_quirk_enable_intel_pch_acs(struct pci_dev *dev)
> >  {
> >       if (!pci_quirk_intel_pch_acs_match(dev))
> > @@ -4973,6 +4980,10 @@ static int pci_quirk_enable_intel_spt_pch_acs(struct pci_dev *dev)
> >       ctrl |= (cap & PCI_ACS_CR);
> >       ctrl |= (cap & PCI_ACS_UF);
> >
> > +     if (dev->external_facing || dev->untrusted)
> > +             /* Translation Blocking */
> > +             ctrl |= (cap & PCI_ACS_TB);
> > +
> >       pci_write_config_dword(dev, pos + INTEL_SPT_ACS_CTRL, ctrl);
> >
> >       pci_info(dev, "Intel SPT PCH root port ACS workaround enabled\n");
> > --
> > 2.27.0.212.ge8ba1cc988-goog
> >