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

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Message-ID: <66cfbc08a457f_473472946a@dwillia2-xfh.jf.intel.com.notmuch>
Date: Wed, 28 Aug 2024 17:08:40 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: D Scott Phillips <scott@...amperecomputing.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

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?