Re: [PATCH] drm/xe: Don't wedge shared engine on stale faults from torn-down VMs

[Matthew Brost <matthew.brost@intel.com>]

On Sat, Sep 12, 2026 at 12:53:01AM +0530, Sanjay Yadav wrote:
> A recoverable page fault generated by a process's completed migrate/BCS
> work can arrive after that process's VM has been closed and its ASID
> removed (abnormal exit while GPU work was in flight).
> xe_pagefault_service() returned an error for such faults, which is
> reported to the GuC/HW as an unsuccessful response. Repeated
> unsuccessful responses eventually escalate to an engine memory CAT
> error. Because the migrate/BCS engine is shared, that CAT error
> wedges it for unrelated processes, which then hang on their own
> copies.

Yikes. Do you have a reproducer for this? I wouldn't expect this
behavior from the hardware, as it appears to violate the expected
process isolation contract.

> 
> Detect stale faults whose owning VM is closed or whose ASID no longer
> maps to a fault-capable VM, and drain them instead of replying
> unsuccessful.
> 
> Cc: Matthew Brost <matthew.brost@intel.com>
> Cc: Stuart Summers <stuart.summers@intel.com>

Fixes, CC stable if this is an issue.

> Assisted-by: GitHub Copilot:claude-opus-4.8
> Signed-off-by: Sanjay Yadav <sanjay.kumar.yadav@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_pagefault.c | 22 +++++++++++++++++++---
>  1 file changed, 19 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_pagefault.c b/drivers/gpu/drm/xe/xe_pagefault.c
> index c82b8bc8bc70..2827652ab8a3 100644
> --- a/drivers/gpu/drm/xe/xe_pagefault.c
> +++ b/drivers/gpu/drm/xe/xe_pagefault.c
> @@ -238,8 +238,10 @@ static struct xe_vm *xe_pagefault_asid_to_vm(struct xe_device *xe, u32 asid)
>  	vm = xa_load(&xe->usm.asid_to_vm, asid);
>  	if (vm && xe_vm_in_fault_mode(vm))
>  		xe_vm_get(vm);
> -	else
> +	else if (vm)
>  		vm = ERR_PTR(-EINVAL);
> +	else
> +		vm = ERR_PTR(-ENOENT);
>  	up_read(&xe->usm.lock);
>  
>  	return vm;
> @@ -260,13 +262,27 @@ static int xe_pagefault_service(struct xe_pagefault *pf)
>  		return -EFAULT;
>  
>  	vm = xe_pagefault_asid_to_vm(xe, asid);
> -	if (IS_ERR(vm))
> +	if (IS_ERR(vm)) {
> +		if (PTR_ERR(vm) == -ENOENT) {
> +			drm_info(&xe->drm,
> +				 "xe_pf_debug: drain stale fault (no VM) asid=%u addr=0x%llx\n",
> +				 asid, pf->consumer.page_addr);
> +			xe_pagefault_set_start_addr(pf, pf->consumer.page_addr);
> +			xe_pagefault_set_end_addr(pf, pf->consumer.page_addr);
> +			return 0;

Won't the page walker hotspin on faults until the executing queue is
descheduled from the hardware if we successfully acknowledge them? That
doesn't seem ideal.

Matt

> +		}
>  		return PTR_ERR(vm);
> +	}
>  
>  	down_read(&vm->lock);
>  
>  	if (xe_vm_is_closed(vm)) {
> -		err = -ENOENT;
> +		drm_info(&xe->drm,
> +			 "xe_pf_debug: drain stale fault (closed VM) asid=%u addr=0x%llx\n",
> +			 asid, pf->consumer.page_addr);
> +		xe_pagefault_set_start_addr(pf, pf->consumer.page_addr);
> +		xe_pagefault_set_end_addr(pf, pf->consumer.page_addr);
> +		err = 0;
>  		goto unlock_vm;
>  	}
>  
> -- 
> 2.52.0
>