[PATCH] drm/amdgpu: skip huge page for PRT mapping

[Christian König]

Am 04.06.2018 um 09:02 schrieb Zhang, Jerry (Junwei):
> On 06/04/2018 02:43 PM, Christian König wrote:
>> Actually that is not correct. According to the documentation the PRT 
>> flag should
>> work for huge pages as well.
>
> Mmm, I checked the doc earlier, didn't find the PRT flag for PDE.

The PDE indeed doesn't have the PRT flag, but it also doesn't have the 
fragment and MTYPE fields and those still work normally when you enable 
huge page handling.

The trick is that when you set the huge page flag then the PDE is 
handled like a PTE and so all the extra fields (PRT, fragment size, 
MTYPE etc...) should now be handled correctly.

Could be that there is a hardware bug related to PRT handling and the 
huge page flag, but at least in theory it should work fine.

>
> In CTS PRT test, the reserved PRT mapping introduces huge page 
> mapping, so later tiled bo mapping cannot make sure the corresponding 
> PTE is set as PRT.
> Then following access triggers VM fault.

Interesting, but that rather sounds like a bug in the handling instead 
of a hardware problem.

Can you narrow down the CTS test further into a libdrm unit test? Or in 
other words what exactly does the CTS test do?

Christian.

>
> Jerry
>
>>
>> Christian.
>>
>> Am 04.06.2018 um 07:59 schrieb Zhou, David(ChunMing):
>>> Good catch, Reviewed-by: Chunming  Zhou <david1.zhou at amd.com>
>>>
>>> -----Original Message-----
>>> From: amd-gfx [mailto:amd-gfx-bounces at lists.freedesktop.org] On 
>>> Behalf Of
>>> Junwei Zhang
>>> Sent: Monday, June 04, 2018 10:04 AM
>>> To: amd-gfx at lists.freedesktop.org
>>> Cc: Zhang, Jerry <Jerry.Zhang at amd.com>
>>> Subject: [PATCH] drm/amdgpu: skip huge page for PRT mapping
>>>
>>> PRT mapping doesn't support huge page, since it's per PTE basis.
>>>
>>> Signed-off-by: Junwei Zhang <Jerry.Zhang at amd.com>
>>> ---
>>>   drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 3 ++-
>>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>>> index 850cd66..4ce8bb0 100644
>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>>> @@ -1111,7 +1111,8 @@ static void amdgpu_vm_handle_huge_pages(struct
>>> amdgpu_pte_update_params *p,
>>>       /* In the case of a mixed PT the PDE must point to it*/
>>>       if (p->adev->asic_type >= CHIP_VEGA10 && !p->src &&
>>> -        nptes == AMDGPU_VM_PTE_COUNT(p->adev)) {
>>> +        nptes == AMDGPU_VM_PTE_COUNT(p->adev) &&
>>> +        !(flags & AMDGPU_PTE_PRT)) {
>>>           /* Set the huge page flag to stop scanning at this PDE */
>>>           flags |= AMDGPU_PDE_PTE;
>>>       }
>>