Re: [PATCH v5] PCI/ACS: Enable PCI_ACS_TB and disable only when needed for ATS

[Rajat Jain <rajatxjain@gmail.com>]

Hello Bjorn,


On Sat, Aug 1, 2020 at 5:30 PM Rajat Jain <rajatja@google.com> wrote:
>
> Hi Bjorn,
>
>
> On Tue, Jul 14, 2020 at 1:24 PM Rajat Jain <rajatxjain@gmail.com> wrote:
> >
> > On Tue, Jul 14, 2020 at 1:15 PM Rajat Jain <rajatja@google.com> wrote:
> > >
> > > The ACS "Translation Blocking" bit blocks the translated addresses from
> > > the devices. We don't expect such traffic from devices unless ATS is
> > > enabled on them. A device sending such traffic without ATS enabled,
> > > indicates malicious intent, and thus should be blocked.
> > >
> > > Enable PCI_ACS_TB by default for all devices, and it stays enabled until
> > > atleast one of the devices downstream wants to enable ATS. It gets
> > > disabled to enable ATS on a device downstream it, and then gets enabled
> > > back on once all the downstream devices don't need ATS.
> > >
> > > Signed-off-by: Rajat Jain <rajatja@google.com>
>
> Just checking to see if you got a chance to look at this V5 patch.

Any feedback on this patch?

Thanks & Best Regards,

Rajat

>
> Thanks & Best Regards,
>
> Rajat
>
> > > ---
> > > Note that I'm ignoring the devices that require quirks to enable or
> > > disable ACS, instead of using the standard way for ACS configuration.
> > > The reason is that it would require adding yet another quirk table or
> > > quirk function pointer, that I don't know how to implement for those
> > > devices, and will neither have the devices to test that code.
> > >
> > > v5: Enable TB and disable ATS for all devices on boot. Disable TB later
> > >     only if needed to enable ATS on downstream devices.
> > > v4: Add braces to avoid warning from kernel robot
> > >     print warning for only external-facing devices.
> > > v3: print warning if ACS_TB not supported on external-facing/untrusted ports.
> > >     Minor code comments fixes.
> > > v2: Commit log change
> > >
> > >  drivers/pci/ats.c   |  5 ++++
> > >  drivers/pci/pci.c   | 57 +++++++++++++++++++++++++++++++++++++++++++++
> > >  drivers/pci/pci.h   |  2 ++
> > >  drivers/pci/probe.c |  2 +-
> > >  include/linux/pci.h |  2 ++
> > >  5 files changed, 67 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
> > > index b761c1f72f67..e2ea9083f30f 100644
> > > --- a/drivers/pci/ats.c
> > > +++ b/drivers/pci/ats.c
> > > @@ -28,6 +28,9 @@ void pci_ats_init(struct pci_dev *dev)
> > >                 return;
> > >
> > >         dev->ats_cap = pos;
> > > +
> > > +       dev->ats_enabled = 1; /* To avoid WARN_ON from pci_disable_ats() */
> > > +       pci_disable_ats(dev);
> > >  }
> > >
> > >  /**
> > > @@ -82,6 +85,7 @@ int pci_enable_ats(struct pci_dev *dev, int ps)
> > >         }
> > >         pci_write_config_word(dev, dev->ats_cap + PCI_ATS_CTRL, ctrl);
> > >
> > > +       pci_disable_acs_trans_blocking(dev);
> > >         dev->ats_enabled = 1;
> > >         return 0;
> > >  }
> > > @@ -102,6 +106,7 @@ void pci_disable_ats(struct pci_dev *dev)
> > >         ctrl &= ~PCI_ATS_CTRL_ENABLE;
> > >         pci_write_config_word(dev, dev->ats_cap + PCI_ATS_CTRL, ctrl);
> > >
> > > +       pci_enable_acs_trans_blocking(dev);
> > >         dev->ats_enabled = 0;
> > >  }
> > >  EXPORT_SYMBOL_GPL(pci_disable_ats);
> > > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > > index 73a862782214..614e3c1e8c56 100644
> > > --- a/drivers/pci/pci.c
> > > +++ b/drivers/pci/pci.c
> > > @@ -876,6 +876,9 @@ static void pci_std_enable_acs(struct pci_dev *dev)
> > >         /* Upstream Forwarding */
> > >         ctrl |= (cap & PCI_ACS_UF);
> > >
> > > +       /* Translation Blocking */
> > > +       ctrl |= (cap & PCI_ACS_TB);
> > > +
> > >         pci_write_config_word(dev, pos + PCI_ACS_CTRL, ctrl);
> > >  }
> > >
> > > @@ -904,6 +907,60 @@ static void pci_enable_acs(struct pci_dev *dev)
> > >         pci_disable_acs_redir(dev);
> > >  }
> > >
> > > +void pci_disable_acs_trans_blocking(struct pci_dev *pdev)
> > > +{
> > > +       u16 cap, ctrl, pos;
> > > +       struct pci_dev *dev;
> > > +
> > > +       if (!pci_acs_enable)
> > > +               return;
> > > +
> > > +       for (dev = pdev; dev; dev = pci_upstream_bridge(pdev)) {
> > > +
> > > +               pos = dev->acs_cap;
> > > +               if (!pos)
> > > +                       continue;
> > > +
> > > +               /*
> > > +                * Disable translation blocking when first downstream
> > > +                * device that needs it (for ATS) wants to enable ATS
> > > +                */
> > > +               if (++dev->ats_dependencies == 1) {
> >
> > I am a little worried about a potential race condition here. I know
> > that 2 PCI devices cannot be enumerating at the same time. Do we know
> > if multiple pci_enable_ats() and pci_disable_ats() function calls can
> > be simultaneously executing (even for different devices)? If so, we
> > may need an atomic_t variable for ats_dependencies.
> >
> > Thanks,
> >
> > Rajat
> >
> >
> > > +                       pci_read_config_word(dev, pos + PCI_ACS_CAP, &cap);
> > > +                       pci_read_config_word(dev, pos + PCI_ACS_CTRL, &ctrl);
> > > +                       ctrl &= ~(cap & PCI_ACS_TB);
> > > +                       pci_write_config_word(dev, pos + PCI_ACS_CTRL, ctrl);
> > > +               }
> > > +       }
> > > +}
> > > +
> > > +void pci_enable_acs_trans_blocking(struct pci_dev *pdev)
> > > +{
> > > +       u16 cap, ctrl, pos;
> > > +       struct pci_dev *dev;
> > > +
> > > +       if (!pci_acs_enable)
> > > +               return;
> > > +
> > > +       for (dev = pdev; dev; dev = pci_upstream_bridge(pdev)) {
> > > +
> > > +               pos = dev->acs_cap;
> > > +               if (!pos)
> > > +                       continue;
> > > +
> > > +               /*
> > > +                * Enable translation blocking when last downstream device
> > > +                * that depends on it (for ATS), doesn't need ATS anymore
> > > +                */
> > > +               if (--dev->ats_dependencies == 0) {
> > > +                       pci_read_config_word(dev, pos + PCI_ACS_CAP, &cap);
> > > +                       pci_read_config_word(dev, pos + PCI_ACS_CTRL, &ctrl);
> > > +                       ctrl |= (cap & PCI_ACS_TB);
> > > +                       pci_write_config_word(dev, pos + PCI_ACS_CTRL, ctrl);
> > > +               }
> > > +       }
> > > +}
> > > +
> > >  /**
> > >   * pci_restore_bars - restore a device's BAR values (e.g. after wake-up)
> > >   * @dev: PCI device to have its BARs restored
> > > diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> > > index 12fb79fbe29d..f5d8ecb6ba96 100644
> > > --- a/drivers/pci/pci.h
> > > +++ b/drivers/pci/pci.h
> > > @@ -552,6 +552,8 @@ static inline int pci_dev_specific_disable_acs_redir(struct pci_dev *dev)
> > >         return -ENOTTY;
> > >  }
> > >  #endif
> > > +void pci_disable_acs_trans_blocking(struct pci_dev *dev);
> > > +void pci_enable_acs_trans_blocking(struct pci_dev *dev);
> > >
> > >  /* PCI error reporting and recovery */
> > >  pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
> > > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> > > index 8c40c00413e7..e2ff3a94e621 100644
> > > --- a/drivers/pci/probe.c
> > > +++ b/drivers/pci/probe.c
> > > @@ -2387,10 +2387,10 @@ static void pci_init_capabilities(struct pci_dev *dev)
> > >         pci_vpd_init(dev);              /* Vital Product Data */
> > >         pci_configure_ari(dev);         /* Alternative Routing-ID Forwarding */
> > >         pci_iov_init(dev);              /* Single Root I/O Virtualization */
> > > +       pci_acs_init(dev);              /* Access Control Services */
> > >         pci_ats_init(dev);              /* Address Translation Services */
> > >         pci_pri_init(dev);              /* Page Request Interface */
> > >         pci_pasid_init(dev);            /* Process Address Space ID */
> > > -       pci_acs_init(dev);              /* Access Control Services */
> > >         pci_ptm_init(dev);              /* Precision Time Measurement */
> > >         pci_aer_init(dev);              /* Advanced Error Reporting */
> > >         pci_dpc_init(dev);              /* Downstream Port Containment */
> > > diff --git a/include/linux/pci.h b/include/linux/pci.h
> > > index 7a40cd5caed0..31da4355f0fd 100644
> > > --- a/include/linux/pci.h
> > > +++ b/include/linux/pci.h
> > > @@ -480,6 +480,8 @@ struct pci_dev {
> > >         u16             ats_cap;        /* ATS Capability offset */
> > >         u8              ats_stu;        /* ATS Smallest Translation Unit */
> > >  #endif
> > > +       /* Total number of downstream devices below a bridge that need ATS */
> > > +       u8              ats_dependencies;
> > >  #ifdef CONFIG_PCI_PRI
> > >         u16             pri_cap;        /* PRI Capability offset */
> > >         u32             pri_reqs_alloc; /* Number of PRI requests allocated */
> > > --
> > > 2.27.0.389.gc38d7665816-goog
> > >