[PATCH] drm/amdgpu: force using sdma to update vm page table when mmio is blocked

[Christian König]

Hi Kevin,

well at least the HDP flush function has to work correctly or otherwise 
the driver won't work correctly.

If the registers are not accessible any more we need to find a proper 
workaround for this.

One possibility would be to use the KIQ, another is a dummy write/read 
to make sure the HDP is flushed (check the hardware docs).

The third option would be to question if blocking the HDP registers is 
really a good idea.

The solution is up to you, but a workaround like proposed below doesn't 
really help in any way.

Regards,
Christian.

Am 20.01.22 um 10:07 schrieb Wang, Yang(Kevin):
>
> [AMD Official Use Only]
>
>
> Hi Chris,
>
> yes, I agree with your point.
> and another way is that we can use KIQ to write HDP register to 
> resolve HDP can't R/W issue.
> but it will cause some performance drop if use KIQ to programing register.
>
> what is your ideas?
>
> Best Regards,
> Kevin
> ------------------------------------------------------------------------
> *From:* Koenig, Christian <Christian.Koenig at amd.com>
> *Sent:* Thursday, January 20, 2022 4:58 PM
> *To:* Wang, Yang(Kevin) <KevinYang.Wang at amd.com>; 
> amd-gfx at lists.freedesktop.org <amd-gfx at lists.freedesktop.org>; 
> Deucher, Alexander <Alexander.Deucher at amd.com>; Liu, Monk 
> <Monk.Liu at amd.com>
> *Cc:* Min, Frank <Frank.Min at amd.com>; Chen, Horace <Horace.Chen at amd.com>
> *Subject:* Re: [PATCH] drm/amdgpu: force using sdma to update vm page 
> table when mmio is blocked
> Well NAK.
>
> Even when we can't R/W HDP registers we need a way to invalidate the 
> HDP or quite a bunch of functions won't work correctly.
>
> Blocking CPU base page table updates only works around the symptoms, 
> but doesn't really solve anything.
>
> Regards,
> Christian.
>
> Am 20.01.22 um 09:46 schrieb Wang, Yang(Kevin):
>>
>> [AMD Official Use Only]
>>
>>
>> ping...
>>
>> add @Liu, Monk <mailto:Monk.Liu at amd.com> @Koenig, Christian 
>> <mailto:Christian.Koenig at amd.com> @Deucher, Alexander 
>> <mailto:Alexander.Deucher at amd.com>
>>
>> Best Regards,
>> Kevin
>> ------------------------------------------------------------------------
>> *From:* Wang, Yang(Kevin) <KevinYang.Wang at amd.com> 
>> <mailto:KevinYang.Wang at amd.com>
>> *Sent:* Wednesday, January 19, 2022 11:16 AM
>> *To:* amd-gfx at lists.freedesktop.org 
>> <mailto:amd-gfx at lists.freedesktop.org> 
>> <amd-gfx at lists.freedesktop.org> <mailto:amd-gfx at lists.freedesktop.org>
>> *Cc:* Min, Frank <Frank.Min at amd.com> <mailto:Frank.Min at amd.com>; 
>> Chen, Horace <Horace.Chen at amd.com> <mailto:Horace.Chen at amd.com>; 
>> Wang, Yang(Kevin) <KevinYang.Wang at amd.com> 
>> <mailto:KevinYang.Wang at amd.com>
>> *Subject:* [PATCH] drm/amdgpu: force using sdma to update vm page 
>> table when mmio is blocked
>> when mmio protection feature is enabled in hypervisor,
>> it will cause guest OS can't R/W HDP regiters,
>> and using cpu to update page table is not working well.
>>
>> force using sdma to update page table when mmio is blocked.
>>
>> Signed-off-by: Yang Wang <KevinYang.Wang at amd.com> 
>> <mailto:KevinYang.Wang at amd.com>
>> ---
>>  drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c 
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>> index b23cb463b106..0f86f0b2e183 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>> @@ -2959,6 +2959,9 @@ int amdgpu_vm_init(struct amdgpu_device *adev, 
>> struct amdgpu_vm *vm)
>>          vm->use_cpu_for_update = !!(adev->vm_manager.vm_update_mode &
>> AMDGPU_VM_USE_CPU_FOR_GFX);
>>
>> +       if (vm->use_cpu_for_update && amdgpu_sriov_vf(adev) && 
>> amdgpu_virt_mmio_blocked(adev))
>> +               vm->use_cpu_for_update = false;
>> +
>>          DRM_DEBUG_DRIVER("VM update mode is %s\n",
>> vm->use_cpu_for_update ? "CPU" : "SDMA");
>>          WARN_ONCE((vm->use_cpu_for_update &&
>> @@ -3094,6 +3097,10 @@ int amdgpu_vm_make_compute(struct 
>> amdgpu_device *adev, struct amdgpu_vm *vm)
>>          /* Update VM state */
>>          vm->use_cpu_for_update = !!(adev->vm_manager.vm_update_mode &
>> AMDGPU_VM_USE_CPU_FOR_COMPUTE);
>> +
>> +       if (vm->use_cpu_for_update && amdgpu_sriov_vf(adev) && 
>> amdgpu_virt_mmio_blocked(adev))
>> +               vm->use_cpu_for_update = false;
>> +
>>          DRM_DEBUG_DRIVER("VM update mode is %s\n",
>> vm->use_cpu_for_update ? "CPU" : "SDMA");
>>          WARN_ONCE((vm->use_cpu_for_update &&
>> -- 
>> 2.25.1
>>
>

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