From: Bjorn Helgaas <helgaas@kernel.org>
To: Rajat Jain <rajatja@google.com>
Cc: Todd Broch <tbroch@google.com>,
linux-pci <linux-pci@vger.kernel.org>,
"Krishnakumar,
Lalithambika" <lalithambika.krishnakumar@intel.com>,
Heikki Krogerus <heikki.krogerus@linux.intel.com>,
Diego Rivas <diegorivas@google.com>,
Jean-Philippe Brucker <jean-philippe@linaro.org>,
Furquan Shaikh <furquan@google.com>,
"Raj, Ashok" <ashok.raj@intel.com>,
Saravana Kannan <saravanak@google.com>,
ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
Christian Kellner <christian@kellner.me>,
Mattias Nissler <mnissler@google.com>,
Jesse Barnes <jsbarnes@google.com>, Len Brown <lenb@kernel.org>,
Rajat Jain <rajatxjain@gmail.com>,
Prashant Malani <pmalani@google.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Aaron Durbin <adurbin@google.com>,
Alex Williamson <alex.williamson@redhat.com>,
Bjorn Helgaas <bhelgaas@google.com>,
Mika Westerberg <mika.westerberg@linux.intel.com>,
Bernie Keany <bernie.keany@intel.com>,
Duncan Laurie <dlaurie@google.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"open list:AMD IOMMU \(AMD-VI\)"
<iommu@lists.linux-foundation.org>, Arnd Bergmann <arnd@arndb.de>,
Oliver O'Halloran <oohall@gmail.com>,
Benson Leung <bleung@google.com>,
David Woodhouse <dwmw2@infradead.org>,
Alex Levin <levinale@google.com>
Subject: Re: [PATCH v4 4/4] PCI/ACS: Enable PCI_ACS_TB for untrusted/external-facing devices
Date: Sat, 11 Jul 2020 14:53:46 -0500 [thread overview]
Message-ID: <20200711195346.GA132330@bjorn-Precision-5520> (raw)
In-Reply-To: <CACK8Z6F-8OZNJU8wqWuZq=moCaOi+3W=CzBeppfO31VZnkqBrg@mail.gmail.com>
On Fri, Jul 10, 2020 at 03:53:59PM -0700, Rajat Jain wrote:
> On Fri, Jul 10, 2020 at 2:29 PM Raj, Ashok <ashok.raj@intel.com> wrote:
> > On Fri, Jul 10, 2020 at 03:29:22PM -0500, Bjorn Helgaas wrote:
> > > On Tue, Jul 07, 2020 at 03:46:04PM -0700, Rajat Jain wrote:
> > > > When enabling ACS, enable translation blocking for external facing ports
> > > > and untrusted devices.
> > > >
> > > > Signed-off-by: Rajat Jain <rajatja@google.com>
> > > > ---
> > > > 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/pci.c | 8 ++++++++
> > > > drivers/pci/quirks.c | 15 +++++++++++++++
> > > > 2 files changed, 23 insertions(+)
> > > >
> > > > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > > > index 73a8627822140..a5a6bea7af7ce 100644
> > > > --- a/drivers/pci/pci.c
> > > > +++ b/drivers/pci/pci.c
> > > > @@ -876,6 +876,14 @@ static void pci_std_enable_acs(struct pci_dev *dev)
> > > > /* Upstream Forwarding */
> > > > ctrl |= (cap & PCI_ACS_UF);
> > > >
> > > > + /* Enable Translation Blocking for external devices */
> > > > + if (dev->external_facing || dev->untrusted) {
> > > > + if (cap & PCI_ACS_TB)
> > > > + ctrl |= PCI_ACS_TB;
> > > > + else if (dev->external_facing)
> > > > + pci_warn(dev, "ACS: No Translation Blocking on external-facing dev\n");
> > > > + }
> > >
> > > IIUC, this means that external devices can *never* use ATS and
> > > can never cache translations.
>
> Yes, but it already exists today (and this patch doesn't change that):
> 521376741b2c2 "PCI/ATS: Only enable ATS for trusted devices"
>
> IMHO any external device trying to send ATS traffic despite having ATS
> disabled should count as a bad intent. And this patch is trying to
> plug that loophole, by blocking the AT traffic from devices that we do
> not expect to see AT from anyway.
Thinking about this some more, I wonder if Linux should:
- Explicitly disable ATS for every device at enumeration-time, e.g.,
in pci_init_capabilities(),
- Enable PCI_ACS_TB for every device (not just external-facing or
untrusted ones),
- Disable PCI_ACS_TB for the relevant devices along the path only
when enabling ATS.
One nice thing about doing that is that the "untrusted" test would be
only in pci_enable_ats(), and we wouldn't need one in
pci_std_enable_acs().
It's possible BIOS gives us devices with ATS enabled, and this might
break them, but that seems like something we'd want to find out about.
Bjorn
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next prev parent reply other threads:[~2020-07-11 19:53 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-07 22:46 [PATCH v4 1/4] PCI: Move pci_enable_acs() and its dependencies up in pci.c Rajat Jain via iommu
2020-07-07 22:46 ` [PATCH v4 2/4] PCI: Keep the ACS capability offset in device Rajat Jain via iommu
2020-07-07 22:46 ` [PATCH v4 3/4] PCI: Treat "external-facing" devices as internal Rajat Jain via iommu
2020-07-07 22:46 ` [PATCH v4 4/4] PCI/ACS: Enable PCI_ACS_TB for untrusted/external-facing devices Rajat Jain via iommu
2020-07-10 20:29 ` Bjorn Helgaas
2020-07-10 21:28 ` Raj, Ashok
2020-07-10 22:53 ` Rajat Jain via iommu
2020-07-10 23:32 ` Bjorn Helgaas
2020-07-11 19:53 ` Bjorn Helgaas [this message]
2020-07-12 0:08 ` Rajat Jain
2020-07-12 2:58 ` Bjorn Helgaas
2020-07-13 8:01 ` Joerg Roedel
2020-07-14 20:19 ` Rajat Jain via iommu
2020-09-15 23:01 ` Rajat Jain via iommu
2020-09-16 21:46 ` Bjorn Helgaas
2020-07-10 20:39 ` [PATCH v4 1/4] PCI: Move pci_enable_acs() and its dependencies up in pci.c Bjorn Helgaas
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