[Intel-gfx] [PATCH v2] drm/i915: Fix a lockdep warning at error capture

[Das, Nirmoy]

On 6/24/2022 2:46 PM, Andrzej Hajda wrote:
> On 24.06.2022 13:08, Nirmoy Das wrote:
>> For some platfroms we use stop_machine version of
>> gen8_ggtt_insert_page/gen8_ggtt_insert_entries to avoid a
>> concurrent GGTT access bug but this causes a circular locking
>> dependency warning:
>>
>>    Possible unsafe locking scenario:
>>          CPU0                    CPU1
>>          ----                    ----
>>     lock(&ggtt->error_mutex);
>>                                  lock(dma_fence_map);
>> lock(&ggtt->error_mutex);
>>     lock(cpu_hotplug_lock);
>>
>> Fix this by calling gen8_ggtt_insert_page/gen8_ggtt_insert_entries
>> directly at error capture which is concurrent GGTT access safe because
>> reset path make sure of that.
>>
>> v2: Fix rebase conflict and added a comment.
>>
>> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5595
>> Reviewed-by: Gwan-gyeong Mun <gwan-gyeong.mun at intel.com>
>> Suggested-by: Chris Wilson <chris at chris-wilson.co.uk>
>> Signed-off-by: Nirmoy Das <nirmoy.das at intel.com>
>> ---
>>   drivers/gpu/drm/i915/gt/intel_ggtt.c     | 10 ++++++++++
>>   drivers/gpu/drm/i915/gt/intel_gtt.h      |  9 +++++++++
>>   drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c |  5 ++++-
>>   drivers/gpu/drm/i915/i915_gpu_error.c    |  8 ++++++--
>>   4 files changed, 29 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/gt/intel_ggtt.c 
>> b/drivers/gpu/drm/i915/gt/intel_ggtt.c
>> index ffff96180313..15a915bb4088 100644
>> --- a/drivers/gpu/drm/i915/gt/intel_ggtt.c
>> +++ b/drivers/gpu/drm/i915/gt/intel_ggtt.c
>> @@ -960,6 +960,16 @@ static int gen8_gmch_probe(struct i915_ggtt *ggtt)
>>       if (intel_vm_no_concurrent_access_wa(i915)) {
>>           ggtt->vm.insert_entries = bxt_vtd_ggtt_insert_entries__BKL;
>>           ggtt->vm.insert_page    = bxt_vtd_ggtt_insert_page__BKL;
>> +
>> +        /*
>> +         * Calling stop_machine() version of GGTT update function
>> +         * at error capture/reset path will raise lockdep warning.
>> +         * Allow calling gen8_ggtt_insert_* directly at reset path
>> +         * which is safe from parallel GGTT updates.
>> +         */
>> +        ggtt->vm.raw_insert_page = gen8_ggtt_insert_page;
>> +        ggtt->vm.raw_insert_entries = gen8_ggtt_insert_entries;
>> +
>>           ggtt->vm.bind_async_flags =
>>               I915_VMA_GLOBAL_BIND | I915_VMA_LOCAL_BIND;
>>       }
>> diff --git a/drivers/gpu/drm/i915/gt/intel_gtt.h 
>> b/drivers/gpu/drm/i915/gt/intel_gtt.h
>> index 29fd3a9e8b2e..e639434e97fd 100644
>> --- a/drivers/gpu/drm/i915/gt/intel_gtt.h
>> +++ b/drivers/gpu/drm/i915/gt/intel_gtt.h
>> @@ -306,6 +306,15 @@ struct i915_address_space {
>>                      struct i915_vma_resource *vma_res,
>>                      enum i915_cache_level cache_level,
>>                      u32 flags);
>> +    void (*raw_insert_page)(struct i915_address_space *vm,
>> +                dma_addr_t addr,
>> +                u64 offset,
>> +                enum i915_cache_level cache_level,
>> +                u32 flags);
>> +    void (*raw_insert_entries)(struct i915_address_space *vm,
>> +                   struct i915_vma_resource *vma_res,
>> +                   enum i915_cache_level cache_level,
>> +                   u32 flags);
>
>
> I would expect rather extra flag to insert_(page|entries) instead of 
> extra callbacks. Anyway both should work.


  I was about to do that but then realized that those flags are closely 
related to PTE attributes so I think it makes sense to keep it that way.


>
> Reviewed-by: Andrzej Hajda <andrzej.hajda at intel.com>


Thanks Andrzej.

>
> Regards
> Andrzej
>
>
>>       void (*cleanup)(struct i915_address_space *vm);
>>         void (*foreach)(struct i915_address_space *vm,
>> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c 
>> b/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c
>> index d2c5c9367cc4..c06e83872c34 100644
>> --- a/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c
>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c
>> @@ -493,7 +493,10 @@ static void uc_fw_bind_ggtt(struct intel_uc_fw 
>> *uc_fw)
>>       if (i915_gem_object_is_lmem(obj))
>>           pte_flags |= PTE_LM;
>>   -    ggtt->vm.insert_entries(&ggtt->vm, dummy, I915_CACHE_NONE, 
>> pte_flags);
>> +    if (ggtt->vm.raw_insert_entries)
>> +        ggtt->vm.raw_insert_entries(&ggtt->vm, dummy, 
>> I915_CACHE_NONE, pte_flags);
>> +    else
>> +        ggtt->vm.insert_entries(&ggtt->vm, dummy, I915_CACHE_NONE, 
>> pte_flags);
>>   }
>>     static void uc_fw_unbind_ggtt(struct intel_uc_fw *uc_fw)
>> diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c 
>> b/drivers/gpu/drm/i915/i915_gpu_error.c
>> index bff8a111424a..f9b1969ed7ed 100644
>> --- a/drivers/gpu/drm/i915/i915_gpu_error.c
>> +++ b/drivers/gpu/drm/i915/i915_gpu_error.c
>> @@ -1104,8 +1104,12 @@ i915_vma_coredump_create(const struct intel_gt 
>> *gt,
>>             for_each_sgt_daddr(dma, iter, vma_res->bi.pages) {
>>               mutex_lock(&ggtt->error_mutex);
>> -            ggtt->vm.insert_page(&ggtt->vm, dma, slot,
>> -                         I915_CACHE_NONE, 0);
>> +            if (ggtt->vm.raw_insert_page)
>> +                ggtt->vm.raw_insert_page(&ggtt->vm, dma, slot,
>> +                             I915_CACHE_NONE, 0);
>> +            else
>> +                ggtt->vm.insert_page(&ggtt->vm, dma, slot,
>> +                             I915_CACHE_NONE, 0);
>>               mb();
>>                 s = io_mapping_map_wc(&ggtt->iomap, slot, PAGE_SIZE);
>