Re: Kernel 5.9 IOMMU groups regression/change

[Rajat Jain <rajatja@google.com>]

On Wed, Oct 28, 2020 at 2:52 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> [+cc Rajat, LKML]
>

Thanks for copying me. (I don't look at mailing lists actively - so
missed this). Taking a look at this now.

Thanks,

Rajat


> On Tue, Oct 27, 2020 at 08:31:09PM +0100, Boris V. wrote:
> > On 25/10/2020 20:45, Boris V. wrote:
> > > With upgrade to kernel 5.9 my VMs stopped working, because some devices
> > > can't be passed through.
> > > This is caused by different IOMMU groups and devices being in the same
> > > group.
> > >
> > > For ex. with kernel 5.8 this are IOMMU groups:
> > > IOMMU Group 40:
> > >         08:01.0 PCI bridge [0604]: ASMedia Technology Inc. Device
> > > [1b21:118f]
> > >         09:00.0 Ethernet controller [0200]: Intel Corporation I211
> > > Gigabit Network Connection [8086:1539] (rev 03)
> > > IOMMU Group 43:
> > >         0c:00.0 SATA controller [0106]: ASMedia Technology Inc. ASM1062
> > > Serial ATA Controller [1b21:0612] (rev 02)
> > > IOMMU Group 44:
> > >         0d:00.0 USB controller [0c03]: ASMedia Technology Inc. ASM1042A
> > > USB 3.0 Host Controller [1b21:1142]
> > >
> > > Ethernet, SATA and USB controller in its own group.
> > >
> > > And with 5.9, everything is in one group:
> > > IOMMU Group 29:
> > >         00:1c.0 PCI bridge [0604]: Intel Corporation C610/X99 series
> > > chipset PCI Express Root Port #1 [8086:8d10] (rev d5)
> > >         00:1c.3 PCI bridge [0604]: Intel Corporation C610/X99 series
> > > chipset PCI Express Root Port #4 [8086:8d16] (rev d5)
> > >         00:1c.4 PCI bridge [0604]: Intel Corporation C610/X99 series
> > > chipset PCI Express Root Port #5 [8086:8d18] (rev d5)
> > >         00:1c.6 PCI bridge [0604]: Intel Corporation C610/X99 series
> > > chipset PCI Express Root Port #7 [8086:8d1c] (rev d5)
> > >         07:00.0 PCI bridge [0604]: ASMedia Technology Inc. Device
> > > [1b21:118f]
> > >         08:01.0 PCI bridge [0604]: ASMedia Technology Inc. Device
> > > [1b21:118f]
> > >         08:03.0 PCI bridge [0604]: ASMedia Technology Inc. Device
> > > [1b21:118f]
> > >         08:04.0 PCI bridge [0604]: ASMedia Technology Inc. Device
> > > [1b21:118f]
> > >         09:00.0 Ethernet controller [0200]: Intel Corporation I211
> > > Gigabit Network Connection [8086:1539] (rev 03)
> > >         0c:00.0 SATA controller [0106]: ASMedia Technology Inc. ASM1062
> > > Serial ATA Controller [1b21:0612] (rev 02)
> > >         0d:00.0 USB controller [0c03]: ASMedia Technology Inc. ASM1042A
> > > USB 3.0 Host Controller [1b21:1142]
> > >
> > >
> > > This seems to be caused by commit
> > > 52fbf5bdeeef415b28b8e6cdade1e48927927f60.
> > > commit 52fbf5bdeeef415b28b8e6cdade1e48927927f60
> > > Author: Rajat Jain <rajatja@google.com>
> > > Date:   Tue Jul 7 15:46:02 2020 -0700
> > >
> > >     PCI: Cache ACS capability offset in device
> > >
> > >     Currently the ACS capability is being looked up at a number of
> > > places. Read
> > >     and store it once at enumeration so that it can be used by all
> > > later.  No
> > >     functional change intended.
> > >
> > >     Link:
> > > https://lore.kernel.org/r/20200707224604.3737893-2-rajatja@google.com
> > >     Signed-off-by: Rajat Jain <rajatja@google.com>
> > >     Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> > >
> > >  drivers/pci/p2pdma.c |  2 +-
> > >  drivers/pci/pci.c    | 20 ++++++++++++++++----
> > >  drivers/pci/pci.h    |  2 +-
> > >  drivers/pci/probe.c  |  2 +-
> > >  drivers/pci/quirks.c |  8 ++++----
> > >  include/linux/pci.h  |  1 +
> > >  6 files changed, 24 insertions(+), 11 deletions(-)
> > >
> > >
> > > If I revert this commit, I get back old groups.
> > >
> > > In commit log there is message 'No functional change intended'. But
> > > there is functional change.
> > >
> > > This is Intel Core i7-5930K CPU and X99 chipset. But I see the same
> > > thing on other Intel systems (didn't test on AMD).
> >
> > Some more info.
> > Problem seems to be that pci_dev_specific_enable_acs() is not called
> > anymore.
> > Before, pci_enable_acs() was called from pci_init_capabilities() and in
> > pci_enable_acs(), pci_dev_specific_enable_acs() was called.
> > I don't know anything about PCI and this stuff, but I'm guessing that this
> > function enable ACS for some Intel devices.
> > But after this commit, pci_acs_init() is called from pci_init_capabilities()
> > and if pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ACS) returns 0,
> > pci_enable_acs() and pci_dev_specific_enable_acs() is not called anymore.
> > If I apply for ex. this patch bellow, groups are right again and everything
> > works as before.
>
> Thanks very much for the report and the debugging.  Maybe we can get
> this sorted and fixed for v5.10-rc2 or -rc3.
>
> > diff -ur linux-5.9.1.orig/drivers/pci/pci.c linux-5.9.1/drivers/pci/pci.c
> > --- linux-5.9.1.orig/drivers/pci/pci.c  2020-10-17 08:31:22.000000000 +0200
> > +++ linux-5.9.1/drivers/pci/pci.c       2020-10-27 19:01:32.650010803 +0100
> > @@ -3502,9 +3502,7 @@
> >  void pci_acs_init(struct pci_dev *dev)
> >  {
> >         dev->acs_cap = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ACS);
> > -
> > -       if (dev->acs_cap)
> > -               pci_enable_acs(dev);
> > +       pci_enable_acs(dev);
> >  }
> >
> >  /**
> >
> >