[PATCH v2] resource: limit request_free_mem_region based on arch_get_mappable_range

[D Scott Phillips]

Dan Williams <dan.j.williams at intel.com> writes:

> D Scott Phillips wrote:
> [..]
>> Hi Dan, sorry for my incredibly delayed response, I lost your message to
>> a filter on my end :(
>> 
>> I'm happy to work toward your preferred approach here, though I'm not
>> sure I know how to achieve it. I think I understand how cxl is keeping
>> device_private_memory out, but I don't think I understand the resource
>> system well enough to see how amdgpu can make a properly trimmed
>> resource for request_free_mem_region. My novice attempt would be
>> something like:
>> 
>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
>> index 8ee3d07ffbdfa..d84de6d66ac45 100644
>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
>> @@ -1038,7 +1039,14 @@ int kgd2kfd_init_zone_device(struct amdgpu_device *adev)
>>                 pgmap->range.end = adev->gmc.aper_base + adev->gmc.aper_size - 1;
>>                 pgmap->type = MEMORY_DEVICE_COHERENT;
>>         } else {
>> -               res = devm_request_free_mem_region(adev->dev, &iomem_resource, size);
>> +               struct range mappable;
>> +               struct resource root;
>> +
>> +               mappable = arch_get_mappable_range();
>> +               root.start = mappable.start;
>> +               root.end = mappable.end;
>> +               root.child = iomem_resource.child;
>> +               res = devm_request_free_mem_region(adev->dev, &root, size);
>>                 if (IS_ERR(res))
>>                         return PTR_ERR(res);
>>                 pgmap->range.start = res->start;
>> 
>> Apart from this being wrong with respect to resource_lock, is that sort
>> of the idea? or am I missing the sensible way to hoist the vmemmap range
>> into iomem_resource? or maybe I'm just totally off in the weeds.
>
> You have the right idea, however, I think a better solution has appeared
> in the meantime. See this recent fix from Thomas regarding collisions
> between KASLR and request_free_mem_region():
>
> http://lore.kernel.org/172418629773.2215.4158024254077335422.tip-bot2@tip-bot2
>
> ...in that case KASLR is limiting the maximum possible usable address
> range that request_free_mem_region() can play. For this
> arch_get_mappable_range() restriction can you adjust the new
> @physmem_end variable for the same effect?

Oh perfect, yes I think that very directly addresses my problem, I'll
handle it that way. Thanks for the pointer Dan.