linux-kernel - [REGRESSION][BISECTED] PCI Passthrough / SR-IOV Failure on Stable Kernel ≥ v6.12.35

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Message-ID: <721D44AF820A4FEB+722679cb-2226-4287-8835-9251ad69a1ac@bbaa.fun>
Date: Mon, 21 Jul 2025 17:59:24 +0800
From: Ban ZuoXiang <bbaa@...a.fun>
To: baolu.lu@...ux.intel.com
Cc: iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
 stable@...r.kernel.org, bbaa@...a.moe
Subject: [REGRESSION][BISECTED] PCI Passthrough / SR-IOV Failure on Stable Kernel ≥ v6.12.35

Hi all,

We've identified a regression affecting PCI passthrough / SR-IOV virtualization starting from Linux v6.12.35.

A user reported that [1], beginning with this version, SR-IOV virtual functions fail to initialize properly inside the guest. The issue appears to some MMIO operations not completing correctly in the guest.

> [    2.152320] i915 0000:07:00.0: [drm] *ERROR* GT0: GUC: mmio request 0x4509: failure 306/0  
> [    2.152327] i915 0000:07:00.0: [drm] *ERROR* GuC initialization failed (-ENXIO)  
> [    2.152330] i915 0000:07:00.0: [drm] *ERROR* GT0: Failed to initialize GPU, declaring it wedged!  

Here is the |git bisect| log:

> # bad: [fbad404f04d758c52bae79ca20d0e7fe5fef91d3] Linux 6.12.37
> # good: [e03ced99c437f4a7992b8fa3d97d598f55453fd0] Linux 6.12.33
> git bisect start 'HEAD' 'v6.12.33'
> # bad: [b01a29a80cca28f0c7d0864e2d62fb9616051bfc] ACPI: bus: Bail out if acpi_kobj registration fails
> git bisect bad b01a29a80cca28f0c7d0864e2d62fb9616051bfc
> # bad: [b01a29a80cca28f0c7d0864e2d62fb9616051bfc] ACPI: bus: Bail out if acpi_kobj registration fails
> git bisect bad b01a29a80cca28f0c7d0864e2d62fb9616051bfc
> # good: [35f116a4658f787bea7e82fdd23e2e9789254f5e] drm/xe: Make xe_gt_freq part of the Documentation
> git bisect good 35f116a4658f787bea7e82fdd23e2e9789254f5e
> # good: [261f2a655b709e59a8d759ce9fa478778d9e84f4] crypto: qat - add shutdown handler to qat_c3xxx
> git bisect good 261f2a655b709e59a8d759ce9fa478778d9e84f4
> # good: [4d0686b53cc9342be3f8ce06336fd5ab0d206355] ata: ahci: Disallow LPM for Asus B550-F motherboard
> git bisect good 4d0686b53cc9342be3f8ce06336fd5ab0d206355
> # bad: [ce4ef0274cb66a4750000f33f2d316c0dbaf4515] KVM: s390: rename PROT_NONE to PROT_TYPE_DUMMY
> git bisect bad ce4ef0274cb66a4750000f33f2d316c0dbaf4515
> # bad: [8d0645b59b19d97a3b7c5a3fb8dae0c89e98cde9] parisc/unaligned: Fix hex output to show 8 hex chars
> git bisect bad 8d0645b59b19d97a3b7c5a3fb8dae0c89e98cde9
> # good: [fed611bd8c7b76b070aa407d0c7558e20d9e1f68] f2fs: fix to do sanity check on ino and xnid
> git bisect good fed611bd8c7b76b070aa407d0c7558e20d9e1f68
> # good: [8a008c89e5e5c5332e4c0a33d707db9ddd529f8a] net/sched: fix use-after-free in taprio_dev_notifier
> git bisect good 8a008c89e5e5c5332e4c0a33d707db9ddd529f8a
> # bad: [3f2098f4fba7718eb2501207ca6e99d22427f25a] fbdev: Fix do_register_framebuffer to prevent null-ptr-deref in fb_videomode_to_var
> git bisect bad 3f2098f4fba7718eb2501207ca6e99d22427f25a
> # bad: [fb5873b779dd5858123c19bbd6959566771e2e83] iommu/vt-d: Restore context entry setup order for aliased devices
> git bisect bad fb5873b779dd5858123c19bbd6959566771e2e83
> # good: [81c64c2f84ab581d1c45dbbbca941c13128faee6] net: ftgmac100: select FIXED_PHY
> git bisect good 81c64c2f84ab581d1c45dbbbca941c13128faee6
> # first bad commit: [fb5873b779dd5858123c19bbd6959566771e2e83] iommu/vt-d: Restore context entry setup order for aliased devices
>
> commit fb5873b779dd5858123c19bbd6959566771e2e83
> Author: Lu Baolu <baolu.lu@...ux.intel.com>
> Date:   Tue May 20 15:58:49 2025 +0800
>
>     iommu/vt-d: Restore context entry setup order for aliased devices
>     
>     commit 320302baed05c6456164652541f23d2a96522c06 upstream.
This commit was introduced in [2], and the issue only affects stable kernels prior to v6.15. Besides, the Ubuntu v6.14-series kernel used by Proxmox also appears to be affected [3].


Best regards,

Ban ZuoXiang

[1]: https://github.com/strongtz/i915-sriov-dkms/issues/320

[2]: https://lore.kernel.org/r/20250514060523.2862195-1-baolu.lu@linux.intel.com

[3]: https://github.com/strongtz/i915-sriov-dkms/issues/312