Re: REGRESSION on linux-next (next-20251106)

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

On 11/18/2025 9:29 AM, Jason Gunthorpe wrote:
> On Mon, Nov 10, 2025 at 12:06:30PM +0530, Borah, Chaitanya Kumar wrote:
>> Hello Jason,
>>
>> Hope you are doing well. I am Chaitanya from the linux graphics team in
>> Intel.
>>
>> This mail is regarding a regression we are seeing in our CI runs[1] on
>> linux-next repository.
>>
>> Since the version next-20251106 [2], we are seeing our tests timing out
>> presumably caused by a GPU Hang.
>>
>> `````````````````````````````````````````````````````````````````````````````````
>> <6> [490.872058] i915 0000:00:02.0: [drm] Got hung context on vcs0 with
>> active request 939:2 [0x1004] not yet started
>> <6> [490.875244] i915 0000:00:02.0: [drm] GPU HANG: ecode 12:4:baffffff
>> <7> [496.424189] i915 0000:00:02.0: [drm:intel_guc_context_reset_process_msg
>> [i915]] GT1: GUC: Got context reset notification: 0x1004 on vcs0, exiting =
>> no, banned = no
>> <6> [496.921551] i915 0000:00:02.0: [drm] Got hung context on vcs0 with
>> active request 939:2 [0x1004] not yet started
>> <6> [496.924799] i915 0000:00:02.0: [drm] GPU HANG: ecode 12:4:baffffff
>> <4> [499.946641] [IGT] Per-test timeout exceeded. Killing the current test
>> with SIGQUIT.
>> `````````````````````````````````````````````````````````````````````````````````
>> Details log can be found in [3].
> Chaitanya, can you check these two debugging patches:
> 
> https://github.com/jgunthorpe/linux/commits/for-borah
> 
> 10635ad3ff26a0 DEBUGGING: Force flush the whole cpu cache for the page table on every map operation
> 2789602b882499 DEBUGGING: Force flush the whole iotlb on every map operation
> 
> Please run a test with each of them applied*individually* and report
> back what changes in the test. The "cpu cache" one may oops or
> something, we are just looking to see if it gets past the error Kevin
> pointed to:
> 
> <7>[   67.231149] [IGT] gem_exec_gttfill: starting subtest basic
> [..]
> <5>[   68.824598] i915 0000:00:02.0: Using 46-bit DMA addresses
> <3>[   68.825482] i915 0000:00:02.0: [drm]*ERROR* GT0: GUC: CT: Failed to process request 6000 (-EOPNOTSUPP)
> 
> I could not test these patches so they may not work at all..

I applied and tested both debugging patches separately, but the failures
persist. And I also tried to flush all TLB caches by adding
flush_tlb_all() in the iommu mapping path. It doesn't help either.

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 2d2f64ce2bc6..59a00235032b 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -3484,6 +3484,8 @@ static int intel_iommu_iotlb_sync_map(struct 
iommu_domain *domain,
  {
         struct dmar_domain *dmar_domain = to_dmar_domain(domain);

+       flush_tlb_all();
+
         if (dmar_domain->iotlb_sync_map)
                 cache_tag_flush_range_np(dmar_domain, iova, iova + size 
- 1);

Thanks,
baolu