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Date:   Wed, 28 Oct 2020 16:52:46 -0500
From:   Bjorn Helgaas <helgaas@kernel.org>
To:     "Boris V." <borisvk@bstnet.org>
Cc:     linux-pci@vger.kernel.org, Rajat Jain <rajatja@google.com>,
        linux-kernel@vger.kernel.org
Subject: Re: Kernel 5.9 IOMMU groups regression/change
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[+cc Rajat, LKML]

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);
> ?}
> 
> ?/**
> 
>