[PATCH] drm/amdgpu: ensure no PCIe peer access for CPU XGMI iolinks

[Christian König]

Am 26.08.22 um 23:49 schrieb Felix Kuehling:
> On 2022-08-26 11:47, Alex Sierra wrote:
>> [Why] Devices with CPU XGMI iolink do not support PCIe peer access.
>>
>> Signed-off-by: Alex Sierra <alex.sierra at amd.com>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c 
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>> index ce7d117efdb5..1ff66718639d 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>> @@ -5538,7 +5538,8 @@ bool amdgpu_device_is_peer_accessible(struct 
>> amdgpu_device *adev,
>>       return pcie_p2p && p2p_access && (adev->gmc.visible_vram_size &&
>>           adev->gmc.real_vram_size == adev->gmc.visible_vram_size &&
>>           !(adev->gmc.aper_base & address_mask ||
>> -          aper_limit & address_mask));
>> +          aper_limit & address_mask) &&
>> +        !adev->gmc.xgmi.connected_to_cpu);
>
> Maybe it would be more readable if you added this to the 
> initialization of p2p_access. In that case you can also save yourself 
> the call to pci_p2pdma_distance_many and all the aperture checks. Like 
> this:
>
>     bool p2p_access = !adev->gmc.xgmi.connected_to_cpu &&
>         !(pci_p2pdma_distance_many(adev->pdev, &peer_adev->dev, 1, 
> true) < 0);

Yeah, agree. Static checks should come first.

But another question: When we have an XGMI link to the CPU all local 
memory is directly accessible, isn't it?

So the PCIe root complex should be able to allow PCIe device to access 
our local memory, even with snooping.

Or do I miss something here?

Regards,
Christian.

>
> Regards,
>   Felix
>
>
>>   #else
>>       return false;
>>   #endif