Re: [PATCH] drm/xe: Use kvmalloc for the VMA ops page-table update array

[karim.sabar@utexas.edu]

Hey Matthew!

Sounds good to me, the fallback of trying to bind the vma one at a time sounds good to me. And it is actually a bit broader than my patch since it covers the -ENOBUFS case as well. It should also be easy to get through drm-xe-fixes and then backported the normal way.

I can write it as a v2 & test it on my Panther Lake device, I have a small repro that does about 20,000 mappings and fails after suspend (every time without the fix). If you'd prefer to write it, I can test your patch as well.

Thanks,
Karim

On Wed, 21 Oct 2026 11:57:48 -0700, Matthew Brost wrote:
> On Tue, Oct 20, 2026 at 07:08:27PM -0500, karim.sabar@utexas.edu wrote:
>> From: Karim Sabar <karim.sabar@utexas.edu>
>> 
>
> Thanks for the patch. I do see the problem in the old code.
> Unfortunately, we will not be able to pull this into drm-xe-next or
> drm-xe-fixes, as 7.3 is already out and 0e33330f1238 is included in our
> 7.4 PR. As a result, this would need to go directly to stable.
>
> There is also a risk that predates the series containing 0e33330f1238.
> If the bind has to run on the GPU, you can still get -ENOBUFS later in
> the bind pipeline if the bind is too large to fit into the
> migration-layer BB. If that occurs, the proper fix may actually be in
> xe_vm_validate_rebind(). If xe_vm_rebind() fails with -ENOBUFS or
> -ENOMEM, we could call a new function, such as xe_vm_rebind_iterative(),
> which would run each VMA requiring a rebind in its own job. This is
> effectively what Mesa does in userspace when a bind operation returns
> -ENOBUFS.
>
> We could probably still pull that approach into drm-xe-fixes + have
> naturally backport to stable, and it may ultimately be the better
> solution.
>
> Let me know what you think. I can give this an RB, but I'd like to hold
> off until we've settled on the solution we want to pursue here.
>
> Matt
>
>> Big games die after every s2idle resume on flat-CCS iGPUs. The exec
>> ioctl keeps returning -ENOMEM even with 11-16 GB of RAM free.
>> 
>> On suspend xe_bo_evict_all_user() evicts every user BO in XE_PL_TT on
>> these parts. On resume the first exec rebinds every VMA in one go and
>> xe_vma_ops_alloc() kmallocs one 384-byte op per VMA as a single array.
>> Final Fantasy VII Rebirth has about 33,500 VMAs which means a 12.9 MB
>> array. It's over the 4 MB KMALLOC_MAX_SIZE and can never succeed.
>> __GFP_NOWARN keeps it out of dmesg.
>> 
>> Data from a Panther Lake handheld (SteamOS kernel 7.2.7), kretprobes
>> after resume:
>>   xe_vma_ops_alloc  -ENOMEM on 63 of 63 attempts
>>   xe_vm_rebind      -ENOMEM on 63 of 63 attempts
>>   BO validate, TTM populate, PT prepare  never failed
>> 
>> The array is only used by the CPU and doesn't need to be contiguous.
>> This switches it to kvmalloc and kvfree.
>> 
>> With the same change applied as a module on that kernel, the game
>> survives every sleep I tried with zero ENOMEM. The biggest array was
>> 30,753 ops (11.8 MB).
>> 
>> drm-xe-next already does this through commit 0e33330f1238 ("drm/xe: Add
>> struct xe_pt_job_ops"), but that's part of a big series that won't go
>> to stable.
>> 
>> I tracked this down and tested it on my own device. I used an AI
>> assistant to help with the debugging, i.e the kprobe tracing and
>> reading through the xe code. I ran every test, picked the fix and
>> reviewed the change myself.
>> 
>> What I couldn't do: this is build-tested on drm-xe-fixes but only
>> run-tested on the SteamOS 7.2.7 kernel through an equivalent module,
>> not on a mainline kernel.
>> 
>> Fixes: 2e524668c440 ("drm/xe: Add xe_vm_pgtable_update_op to xe_vma_ops")
>> Cc: stable@vger.kernel.org # v6.11+
>> Assisted-by: Claude:claude-opus-5-5
>> Signed-off-by: Karim Sabar <karim.sabar@utexas.edu>
>> ---
>> Downstream SteamOS report with the same data: https://github.com/ValveSoftware/SteamOS/issues/2962
>> ---
>>  drivers/gpu/drm/xe/xe_vm.c | 8 ++++----
>>  1 file changed, 4 insertions(+), 4 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
>> index 99e42bd29..5caef443b 100644
>> --- a/drivers/gpu/drm/xe/xe_vm.c
>> +++ b/drivers/gpu/drm/xe/xe_vm.c
>> @@ -703,9 +703,9 @@ static int xe_vma_ops_alloc(struct xe_vma_ops *vops, bool array_of_binds)
>>  			continue;
>>  
>>  		vops->pt_update_ops[i].ops =
>> -			kmalloc_objs(*vops->pt_update_ops[i].ops,
>> -				     vops->pt_update_ops[i].num_ops,
>> -				     GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_NOWARN);
>> +			kvmalloc_objs(*vops->pt_update_ops[i].ops,
>> +				      vops->pt_update_ops[i].num_ops,
>> +				      GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_NOWARN);
>>  		if (!vops->pt_update_ops[i].ops)
>>  			return array_of_binds ? -ENOBUFS : -ENOMEM;
>>  	}
>> @@ -742,7 +742,7 @@ static void xe_vma_ops_fini(struct xe_vma_ops *vops)
>>  	xe_vma_svm_prefetch_ops_fini(vops);
>>  
>>  	for (i = 0; i < XE_MAX_TILES_PER_DEVICE; ++i)
>> -		kfree(vops->pt_update_ops[i].ops);
>> +		kvfree(vops->pt_update_ops[i].ops);
>>  }
>>  
>>  static void xe_vma_ops_incr_pt_update_ops(struct xe_vma_ops *vops, u8 tile_mask, int inc_val)
>> 
>> ---
>> base-commit: d2ce8fcd778ee6d92748c92d23a56d4416c29d86
>> change-id: 20261020-xe-kvmalloc-vma-ops-2637ebf81cfd
>> 
>> Best regards,
>> --  
>> Karim Sabar <karim.sabar@utexas.edu>
>>