linux-kernel - Re: [PATCH v2] resource: limit request_free_mem_region based on arch_get_mappable

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Message-ID: <86v7zjl01j.fsf@scott-ph-mail.amperecomputing.com>
Date: Thu, 29 Aug 2024 10:19:04 -0700
From: D Scott Phillips <scott@...amperecomputing.com>
To: Dan Williams <dan.j.williams@...el.com>, Dan Williams
 <dan.j.williams@...el.com>, Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>, Andy Shevchenko
 <andriy.shevchenko@...ux.intel.com>, AKASHI Takahiro
 <takahiro.akashi@...aro.org>, Alison Schofield
 <alison.schofield@...el.com>, Baoquan He <bhe@...hat.com>, Catalin Marinas
 <catalin.marinas@....com>, Will
 Deacon <will@...nel.org>, linux-kernel@...r.kernel.org
Cc: linux-arm-kernel@...ts.infradead.org, Andrew Morton
 <akpm@...ux-foundation.org>, "Kirill A. Shutemov"
 <kirill.shutemov@...ux.intel.com>, patches@...erecomputing.com, Felix
 Kuehling <Felix.Kuehling@....com>, amd-gfx@...ts.freedesktop.org
Subject: Re: [PATCH v2] resource: limit request_free_mem_region based on
 arch_get_mappable_range

Dan Williams <dan.j.williams@...el.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.