Re: [RFC PATCH RESEND] iommu: intel: apply quirk_iommu_igfx for 8086:0044 (QM57/QS57)

[Baolu Lu <baolu.lu@linux.intel.com>]

On 4/18/25 11:07, Baolu Lu wrote:
> On 1/20/25 17:35, Mingcong Bai wrote:
>> (I'm not very confident about the approach of this patch but I failed to
>> find a better way to address the issue I have on hand, so please consider
>> this patch as an RFC...)
>>
>> On the Lenovo ThinkPad X201, when Intel VT-d is enabled in the BIOS, the
>> kernel boots with errors related to DMAR, the graphical interface 
>> appeared
>> quite choppy, and the system resets erratically within a minute after it
>> booted:
>>
>> DMAR: DRHD: handling fault status reg 3
>> DMAR: [DMA Write NO_PASID] Request device [00:02.0] fault addr 0xb97ff000
>> [fault reason 0x05] PTE Write access is not set
>>
>> Upon comparing boot logs with VT-d on/off, I found that the Intel 
>> Calpella
>> quirk (`quirk_calpella_no_shadow_gtt()') correctly applied the igfx IOMMU
>> disable/quirk correctly:
>>
>> pci 0000:00:00.0: DMAR: BIOS has allocated no shadow GTT; disabling IOMMU
>> for graphics
>>
>> Whereas with VT-d on, it went into the "else" branch, which then
>> triggered the DMAR handling fault above:
>>
>> ... else if (!disable_igfx_iommu) {
>>     /* we have to ensure the gfx device is idle before we flush */
>>     pci_info(dev, "Disabling batched IOTLB flush on Ironlake\n");
>>     iommu_set_dma_strict();
>> }
>>
>> Now, this is not exactly scientific, but moving 0x0044 to 
>> quirk_iommu_igfx
>> seems to have fixed the aforementioned issue. Running a few `git blame'
>> runs on the function, I have found that the quirk was originally
>> introduced as a fix specific to ThinkPad X201:
>>
>> commit 9eecabcb9a92 ("intel-iommu: Abort IOMMU setup for igfx if BIOS 
>> gave
>> no shadow GTT space")
>>
>> Which was later revised twice to the "else" branch we saw above:
>>
>> - 2011: commit 6fbcfb3e467a ("intel-iommu: Workaround IOTLB hang on
>>    Ironlake GPU")
>> - 2024: commit ba00196ca41c ("iommu/vt-d: Decouple igfx_off from graphic
>>    identity mapping")
>>
>> I'm uncertain whether further testings on this particular laptops were
>> done in 2011 and (honestly I'm not sure) 2024, but I would be happy to do
>> some distro-specific testing if that's what would be required to verify
>> this patch.
>>
>> P.S., I also see IDs 0x0040, 0x0062, and 0x006a listed under the same
>> `quirk_calpella_no_shadow_gtt()' quirk, but I'm not sure how similar 
>> these
>> chipsets are (if they share the same issue with VT-d or even, indeed, if
>> this issue is specific to a bug in the Lenovo BIOS). With regards to
>> 0x0062, it seems to be a Centrino wireless card, but not a chipset?
>>
>> I have also listed a couple (distro and kernel) bug reports below as
>> references (some of them are from 7-8 years ago!), as they seem to be
>> similar issue found on different Westmere/Ironlake, Haswell, and 
>> Broadwell
>> hardware setups.
>>
>> Link:https://bugzilla.kernel.org/show_bug.cgi?id=197029
>> Link:https://groups.google.com/g/qubes-users/c/4NP4goUds2c?pli=1
>> Link:https://bugs.archlinux.org/task/65362
>> Link:https://bbs.archlinux.org/viewtopic.php?id=230323
>> Reported-by: Wenhao Sun<weiguangtwk@outlook.com>
>> Signed-off-by: Mingcong Bai<jeffbai@aosc.io>
>> ---
>>   drivers/iommu/intel/iommu.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> Queued for v6.15-rc. Thank you!

Please ignore this. I picked the latest one instead.

https://lore.kernel.org/r/20250415133330.12528-1-jeffbai@aosc.io

Sorry for the inconvenience.