[PATCH] drm/amdkfd: Relocate TBA/TMA to opposite side of VM hole (v2)

[Felix Kuehling]

On 2024-01-29 11:50, Arunpravin Paneer Selvam wrote:
>>>> @@ -339,18 +346,19 @@ static void kfd_init_apertures_v9(struct
>>>> kfd_process_device *pdd, uint8_t id)
>>>>        pdd->lds_base = MAKE_LDS_APP_BASE_V9();
>>>>        pdd->lds_limit = MAKE_LDS_APP_LIMIT(pdd->lds_base);
>>>>
>>>> -        /* Raven needs SVM to support graphic handle, etc. Leave 
>>>> the small
>>>> -         * reserved space before SVM on Raven as well, even though 
>>>> we don't
>>>> -         * have to.
>>>> -         * Set gpuvm_base and gpuvm_limit to CANONICAL addresses 
>>>> so that they
>>>> -         * are used in Thunk to reserve SVM.
>>>> -         */
>>>> -        pdd->gpuvm_base = SVM_USER_BASE;
>>>> +      pdd->gpuvm_base = AMDGPU_VA_RESERVED_BOTTOM;
>>> Hi Felix,
>>>
>>> pdd->gpuvm_base changes from 16KB to 2MB after this patch.
>>>
>>> The default mmap_min_addr(/proc/sys/vm/mmap_min_addr) is 64KB.
>>>
>>> That means user could get a CPU VA < 2MB while the corresponding GPU 
>>> VA has been reserved. Will this break SVM?
>>
>> It could break SVM if a process tries to map or access something 
>> below 2MB. I'm not sure what AMDGPU_VA_RESERVED_BOTTOM is used for in 
>> the GPU page tables. But if it's causing problems for real 
>> applications with SVM, we should look into lowering that reservation.
>>
> We have decided to keep AMDGPU_VA_RESERVED_BOTTOM free for catching 
> NULL pointer dereferences.

Can this be made smaller? I think the 64KB minimum address used on the 
CPU side serves the same purpose. Could we match that on the GPU side?

Regards,
   Felix


>
> Regards,
> Arun.