Re: [PATCH V1] accel/amdxdna: Serialize HMM range faults on one umap

[Lizhi Hou <lizhi.hou@amd.com>]

On 10/12/26 21:38, Matthew Brost wrote:
> On Mon, Oct 12, 2026 at 09:10:15PM -0700, Max Zhen wrote:
>>
>> On 10/12/2026 Mon 13:31, Lizhi Hou wrote:
>>> Two hardware contexts can submit jobs that use the same GEM object while
>>> a user mapping is invalid. aie2_cmd_submit() drops the reservation and
>>> notifier_lock before aie2_populate_range(), and that function takes a
>>> reference on the first invalid umap without clearing invalid until the
>>> fault returns. Both submissions then call
>>> hmm_range_fault_unlocked_timeout() on the same struct hmm_range. That
>>> structure is not safe for concurrent callers. The calls write
>>> notifier_seq and hmm_pfns[] at the same time, so mmu_interval_read_retry()
>>> can see the other call's sequence, miss an invalidation, and clear
>>> invalid. The job is then pushed while the pages may already be gone.
>>> Give each umap its own mutex and hold it from the fault through the retry
>>> check and the store that clears invalid. notifier_lock is dropped before
>>> this mutex is taken, and the fault drops mmap_lock before notifier_lock
>>> is taken again.
>>>
>>> Fixes: aac243092b70 ("accel/amdxdna: Add command execution")
>>> Signed-off-by: Lizhi Hou <lizhi.hou@amd.com>
>> Reviewed-by: Max Zhen <max.zhen@amd.com>
> I was browsing dri-devel and this hmm interaction annoyed me enough to
> ask my AI to fix this and converge properly on a DRM framework:
>
> https://gitlab.freedesktop.org/mbrost/xe-kernel-driver-svn-perf-6-15-2025/-/commits/local_dev/amd_hmm_cleanup

The patch looks clean.  I pull it on top of latest drm-misc-next and run 
some regression tests. It works fine too. :)

Lizhi

>
> Improper HMM or abuse affects the entire kernel, hence we should
> converge.
>
> Please consider the AI suggestions (last 3 patches) instead of open
> coding this.
>
> Matt
>
>>> ---
>>>    drivers/accel/amdxdna/aie2_ctx.c    | 7 ++++++-
>>>    drivers/accel/amdxdna/amdxdna_gem.c | 2 ++
>>>    drivers/accel/amdxdna/amdxdna_gem.h | 1 +
>>>    3 files changed, 9 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/accel/amdxdna/aie2_ctx.c b/drivers/accel/amdxdna/aie2_ctx.c
>>> index d927c8c9d557..4db67a789c34 100644
>>> --- a/drivers/accel/amdxdna/aie2_ctx.c
>>> +++ b/drivers/accel/amdxdna/aie2_ctx.c
>>> @@ -1155,19 +1155,24 @@ static int aie2_populate_range(struct amdxdna_gem_obj *abo)
>>>    		return -EFAULT;
>>>    	}
>>> +	mutex_lock(&mapp->lock);
>>>    	ret = hmm_range_fault_unlocked_timeout(&mapp->range, timeout);
>>> -	if (ret)
>>> +	if (ret) {
>>> +		mutex_unlock(&mapp->lock);
>>>    		goto put_mm;
>>> +	}
>>>    	down_write(&xdna->notifier_lock);
>>>    	if (mmu_interval_read_retry(&mapp->notifier, mapp->range.notifier_seq)) {
>>>    		up_write(&xdna->notifier_lock);
>>> +		mutex_unlock(&mapp->lock);
>>>    		amdxdna_umap_put(mapp);
>>>    		mmput(mm);
>>>    		goto again;
>>>    	}
>>>    	mapp->invalid = false;
>>>    	up_write(&xdna->notifier_lock);
>>> +	mutex_unlock(&mapp->lock);
>>>    	amdxdna_umap_put(mapp);
>>>    	mmput(mm);
>>>    	goto again;
>>> diff --git a/drivers/accel/amdxdna/amdxdna_gem.c b/drivers/accel/amdxdna/amdxdna_gem.c
>>> index f14484bc31ec..37bfa5058095 100644
>>> --- a/drivers/accel/amdxdna/amdxdna_gem.c
>>> +++ b/drivers/accel/amdxdna/amdxdna_gem.c
>>> @@ -318,6 +318,7 @@ static void amdxdna_umap_release(struct kref *ref)
>>>    	struct amdxdna_umap *mapp = container_of(ref, struct amdxdna_umap, refcnt);
>>>    	mmu_interval_notifier_remove(&mapp->notifier);
>>> +	mutex_destroy(&mapp->lock);
>>>    	kvfree(mapp->range.hmm_pfns);
>>>    	kfree(mapp);
>>>    }
>>> @@ -402,6 +403,7 @@ static int amdxdna_hmm_register(struct amdxdna_gem_obj *abo,
>>>    		goto free_pfns;
>>>    	}
>>> +	mutex_init(&mapp->lock);
>>>    	down_write(&xdna->notifier_lock);
>>>    	if (list_empty(&abo->mem.umap_list))
>>>    		abo->mem.uva = addr;
>>> diff --git a/drivers/accel/amdxdna/amdxdna_gem.h b/drivers/accel/amdxdna/amdxdna_gem.h
>>> index 9b4aa21a37c9..456a537eb68c 100644
>>> --- a/drivers/accel/amdxdna/amdxdna_gem.h
>>> +++ b/drivers/accel/amdxdna/amdxdna_gem.h
>>> @@ -19,6 +19,7 @@ struct amdxdna_umap {
>>>    	struct kref			refcnt;
>>>    	bool				invalid;
>>>    	bool				unmapped;
>>> +	struct mutex			lock; /* protect range */
>>>    };
>>>    struct amdxdna_mem {