[pve-devel] [PATCH pve-kernel/master 2/2] revert Ubuntu patch disabling IOMMU functionality for Skylake iGPU

[Stoiko Ivanov]

This change breaks passthrough of the iGPU on older Intel Plattforms
(Skylake)
https://forum.proxmox.com/threads/.157266

The patch was orignally applied by Ubuntu upstream for an issue
unrelated to passthrough - flickering of the display with these chips,
where some comments suggest that setting intel_iommu=igfx_off does not
fix the issue, while the patch explicitly says it does the same as
setting intel_iommu=igfx_off - my quick glance at the code agrees with
the patch author, with the downside that with the patch you cannot
enable it again via kernel_cmdline.
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2062951

As this is a regression, and our user-base does not seem to have
encountered the issue with flickering displays simply revert the
change for now. A proper fix seems to be in the makings in linux
upstream (according to the launchpad issue)

I tested this on an old machine we had lying around - reverting the
patch suppressed the message:
pci 0000:00:02.0: DMAR: Disabling IOMMU for graphics on this chipset
(also did not notice any flickering in a short graphic session
(wayland+kde)).

I'd suggest pulling this also into our 6.8 kernel (but this can also happen
after we get some feedback that it indeed fixes the issue of the
reporters in the forum)

Signed-off-by: Stoiko Ivanov <s.ivanov at proxmox.com>
---
 ...UCE-iommu-intel-disable-DMAR-for-SKL.patch | 53 +++++++++++++++++++
 1 file changed, 53 insertions(+)
 create mode 100644 patches/kernel/0017-Revert-UBUNTU-SAUCE-iommu-intel-disable-DMAR-for-SKL.patch

diff --git a/patches/kernel/0017-Revert-UBUNTU-SAUCE-iommu-intel-disable-DMAR-for-SKL.patch b/patches/kernel/0017-Revert-UBUNTU-SAUCE-iommu-intel-disable-DMAR-for-SKL.patch
new file mode 100644
index 000000000000..2c1a265d0d59
--- /dev/null
+++ b/patches/kernel/0017-Revert-UBUNTU-SAUCE-iommu-intel-disable-DMAR-for-SKL.patch
@@ -0,0 +1,53 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Stoiko Ivanov <s.ivanov at proxmox.com>
+Date: Mon, 25 Nov 2024 11:10:35 +0100
+Subject: [PATCH] Revert "UBUNTU: SAUCE: iommu/intel: disable DMAR for SKL
+ integrated gfx"
+
+Some of our users use the iGPU for PCI-passthrough on those
+plattforms, which seems broken with this commit added.
+https://forum.proxmox.com/threads/.157266
+
+This reverts commit b310f5f58c83756fc164f7d391d76f0df9cc65c3.
+---
+ drivers/iommu/intel/iommu.c | 27 ---------------------------
+ 1 file changed, 27 deletions(-)
+
+diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
+index 34c8b02ca7878..a27cbc22148fa 100644
+--- a/drivers/iommu/intel/iommu.c
++++ b/drivers/iommu/intel/iommu.c
+@@ -4766,33 +4766,6 @@ DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x1632, quirk_iommu_igfx);
+ DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x163A, quirk_iommu_igfx);
+ DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x163D, quirk_iommu_igfx);
+ 
+-/* SKL */
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x1906, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x1913, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x190E, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x1915, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x1902, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x190A, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x190B, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x1917, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x1916, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x1921, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x191E, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x1912, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x191A, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x191B, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x191D, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x1923, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x1926, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x1927, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x192A, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x192B, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x192D, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x1932, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x193A, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x193B, quirk_iommu_igfx);
+-DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x193D, quirk_iommu_igfx);
+-
+ /* disable IPU dmar support */
+ DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, PCI_ANY_ID, quirk_iommu_ipu);
+ 
-- 
2.39.5