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

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

On 11/19/2025 12:13 AM, Jason Gunthorpe wrote:
>> Also, the tests fail consistently and are not sporadic.
>  From these logs I see the below fragment, noting this:
> 
>   gem_exec_gttfil-1010    [004] .N...    50.126420: map: IOMMU: iova=0x00003fffffc00000 - 0x0000400000000000 paddr=0x00000001b9400000 size=4194304
>                                                                      ^^^^^^^^^^^^^^^^^^^
> Which is the high IOVA.. It has bit 45 set. I fed this mapping into
> the kunit and it does map successfully.
> 
> It is not high enough to get into anything special about sign extend,
> the driver sets:
> 
> 	if (cap_fl5lp_support(iommu->cap))
> 		cfg.common.hw_max_vasz_lg2 = 57;
> 	else
> 		cfg.common.hw_max_vasz_lg2 = 48;
> 
> Maybe this code is wrong? Baolu what did you get for this log:
> 
>   [   50.126166] i915 0000:00:02.0: Using 46-bit DMA addresses
> 
> In your force second stage test? Is it 46? Second stage uses different
> code to compute vasz_lg2 and is sensitive to magw:
> 
> 	if (mgaw >= 48 && (sagaw & BIT(3)))
> 		return min(57, mgaw);
> 	else if (mgaw >= 39 && (sagaw & BIT(2)))
> 		return min(48, mgaw);
> 	else if (mgaw >= 30 && (sagaw & BIT(1)))
> 		return min(39, mgaw);
> 
> Maybe this is the issue?

When first stage translation is used,

	cfg.common.hw_max_vasz_lg2 = 48

When second stage translation is used,

	cfg.common.hw_max_vasz_lg2 = 42

Interesting thing is if I hardcode

	cfg.common.hw_max_vasz_lg2 = 42

for the first stage translation, it works.

The only change that I have made to achieve this likes below:

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 2d2f64ce2bc6..a505bba8dcc7 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -2813,10 +2813,13 @@ intel_iommu_domain_alloc_first_stage(struct 
device *dev,
         if (IS_ERR(dmar_domain))
                 return ERR_CAST(dmar_domain);

+#if 0
         if (cap_fl5lp_support(iommu->cap))
                 cfg.common.hw_max_vasz_lg2 = 57;
         else
                 cfg.common.hw_max_vasz_lg2 = 48;
+#endif
+       cfg.common.hw_max_vasz_lg2 = 42;
         cfg.common.hw_max_oasz_lg2 = 52;
         cfg.common.features = BIT(PT_FEAT_SIGN_EXTEND) |
                               BIT(PT_FEAT_FLUSH_RANGE);

Thanks,
baolu