[Intel-gfx] [PATCH 1/5] drm/i915/guc: Don't GEM_BUG_ON on corrupted G2H CTB

[Michal Wajdeczko]

On Thu, 16 Jan 2020 19:46:35 +0100, Daniele Ceraolo Spurio  
<daniele.ceraolospurio at intel.com> wrote:

>
>
> On 1/15/20 6:08 AM, Michal Wajdeczko wrote:
>> We should never BUG_ON on any corruption in CTB descriptor as
>> data there can be also modified by the GuC. Instead we can
>> use flag "is_in_error" to indicate that we will not process
>> any further messages over this CTB (until reset). While here
>> move descriptor error reporting to the function that actually
>> touches that descriptor.
>>  Note that unexpected content of the specific CT messages, that
>> still complies with generic CT message format, shall not trigger
>> disabling whole CTB, as that might just indicate new unsupported
>> message types.
>>  Signed-off-by: Michal Wajdeczko <michal.wajdeczko at intel.com>
>> Cc: Chris Wilson <chris at chris-wilson.co.uk>
>> Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
>> ---
>>   drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c | 42 ++++++++++++++---------
>>   1 file changed, 26 insertions(+), 16 deletions(-)
>>  diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c  
>> b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
>> index a55c336cc5ef..0d3556a820a3 100644
>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
>> @@ -578,19 +578,29 @@ static inline bool ct_header_is_response(u32  
>> header)
>>   static int ctb_read(struct intel_guc_ct_buffer *ctb, u32 *data)
>>   {
>>   	struct guc_ct_buffer_desc *desc = ctb->desc;
>> -	u32 head = desc->head / 4;	/* in dwords */
>> -	u32 tail = desc->tail / 4;	/* in dwords */
>> -	u32 size = desc->size / 4;	/* in dwords */
>> +	u32 head = desc->head;
>> +	u32 tail = desc->tail;
>> +	u32 size = desc->size;
>>   	u32 *cmds = ctb->cmds;
>> -	s32 available;			/* in dwords */
>> +	s32 available;
>>   	unsigned int len;
>>   	unsigned int i;
>>   -	GEM_BUG_ON(desc->size % 4);
>> -	GEM_BUG_ON(desc->head % 4);
>> -	GEM_BUG_ON(desc->tail % 4);
>> -	GEM_BUG_ON(tail >= size);
>> -	GEM_BUG_ON(head >= size);
>> +	if (unlikely(desc->is_in_error))
>> +		return -EPIPE;
>
> How do we recover from this situation? before we marked the buffer as  
> in_error but didn't stop processing of G2H, but with this return here we  
> do. Do we need to reset the CTB desc to recover?

before we should hit BUG_ON followed by PANIC (since we read in irq)
now (or soon) we should be able to detect stalled CTB and then wedge
we can't reset CTB alone as IIRC GuC keeps its own head/tail copies

>
>> +
>> +	if (unlikely(!IS_ALIGNED(head, 4) ||
>> +		     !IS_ALIGNED(tail, 4) ||
>> +		     !IS_ALIGNED(size, 4) ||
>> +		     (tail >= size) || (head >= size))) {
>> +		DRM_ERROR("CT: Invalid data in descriptor\n");
>
> nit: this log is redundant since we have a better message after the jump  
> which includes the values

yeah, looking again and agree that's redundant, will remove

Initially this "better message" was here, then it was reduced after copying
it after jump to allow below error also to have desc details:

	DRM_ERROR("CT: incomplete message %*ph %*ph %*ph\n",

>
> Daniele
>
>> +		goto corrupted;
>> +	}
>> +
>> +	/* later calculations will be done in dwords */
>> +	head /= 4;
>> +	tail /= 4;
>> +	size /= 4;
>>     	/* tail == head condition indicates empty */
>>   	available = tail - head;
>> @@ -615,7 +625,7 @@ static int ctb_read(struct intel_guc_ct_buffer  
>> *ctb, u32 *data)
>>   			       size - head : available - 1), &cmds[head],
>>   			  4 * (head + available - 1 > size ?
>>   			       available - 1 - size + head : 0), &cmds[0]);
>> -		return -EPROTO;
>> +		goto corrupted;
>>   	}
>>     	for (i = 1; i < len; i++) {
>> @@ -626,6 +636,12 @@ static int ctb_read(struct intel_guc_ct_buffer  
>> *ctb, u32 *data)
>>     	desc->head = head * 4;
>>   	return 0;
>> +
>> +corrupted:
>> +	DRM_ERROR("CT: Corrupted descriptor addr=%#x head=%u tail=%u  
>> size=%u\n",
>> +		  desc->addr, desc->head, desc->tail, desc->size);
>> +	desc->is_in_error = 1;
>> +	return -EPIPE;
>>   }
>>     /**
>> @@ -836,10 +852,4 @@ void intel_guc_ct_event_handler(struct  
>> intel_guc_ct *ct)
>>   		else
>>   			err = ct_handle_request(ct, msg);
>>   	} while (!err);
>> -
>> -	if (GEM_WARN_ON(err == -EPROTO)) {
>> -		CT_ERROR(ct, "Corrupted message: %#x\n", msg[0]);
>> -		ctb->desc->is_in_error = 1;
>> -	}
>>   }
>> -