linux-kernel - Re: [PATCH -v2] resource: Remove dependency on SPARSEMEM from GET_FREE

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Message-ID: <20241016153833.GA385255@thelio-3990X>
Date: Wed, 16 Oct 2024 08:38:33 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Huang Ying <ying.huang@...el.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Dan Williams <dan.j.williams@...el.com>,
	Guenter Roeck <linux@...ck-us.net>, Arnd Bergmann <arnd@...db.de>,
	David Hildenbrand <david@...hat.com>,
	Jonathan Cameron <jonathan.cameron@...wei.com>
Subject: Re: [PATCH -v2] resource: Remove dependency on SPARSEMEM from
 GET_FREE_REGION

On Wed, Oct 16, 2024 at 09:47:30AM +0800, Huang Ying wrote:
> We want to use the functions (get_free_mem_region()) configured via
> GET_FREE_REGION in resource kunit tests.  However, GET_FREE_REGION
> depends on SPARSEMEM now.  This makes resource kunit tests cannot be
> built on some architectures lacking SPARSEMEM, or causes config
> warning as follows,
> 
>   WARNING: unmet direct dependencies detected for GET_FREE_REGION
>   Depends on [n]: SPARSEMEM [=n]
>   Selected by [y]:
>   - RESOURCE_KUNIT_TEST [=y] && RUNTIME_TESTING_MENU [=y] && KUNIT [=y]
> 
> When get_free_mem_region() was introduced the only consumers were
> those looking to pass the address range to memremap_pages(). That
> address range needed to be mindful of the maximum addressable platform
> physical address which at the time only SPARSMEM defined via
> MAX_PHYSMEM_BITS.
> 
> Given that memremap_pages() also depended on SPARSEMEM via
> ZONE_DEVICE, it was easier to just depend on that definition than
> invent a general MAX_PHYSMEM_BITS concept outside of SPARSEMEM.
> 
> Turns out that decision was buggy and did not account for KASAN
> consumption of physical address space. That problem was resolved
> recently with commit ea72ce5da228 ("x86/kaslr: Expose and use the end
> of the physical memory address space"), and GET_FREE_REGION dropped
> its MAX_PHYSMEM_BITS dependency.
> 
> Then commit 99185c10d5d9 ("resource, kunit: add test case for
> region_intersects()"), went ahead and fixed up the only remaining
> dependency on SPARSEMEM which was usage of the PA_SECTION_SHIFT macro
> for setting the default alignment. A PAGE_SIZE fallback is fine in the
> SPARSEMEM=n case.
> 
> With those build dependencies gone GET_FREE_REGION no longer depends
> on SPARSEMEM.  So, the patch removes dependency on SPARSEMEM from
> GET_FREE_REGION to fix the build issues.
> 
> Link: https://lore.kernel.org/lkml/20240922225041.603186-1-linux@roeck-us.net/
> Fixes: 99185c10d5d9 ("resource, kunit: add test case for region_intersects()")
> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
> Co-developed-by: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> Tested-by: Guenter Roeck <linux@...ck-us.net>

Tested-by: Nathan Chancellor <nathan@...nel.org> # build

Thanks for adding the Fixes tag, as this should go via -hotfixes.

> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Jonathan Cameron <jonathan.cameron@...wei.com>
> ---
>  mm/Kconfig | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 4c9f5ea13271..33fa51d608dc 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -1085,7 +1085,6 @@ config HMM_MIRROR
>  	depends on MMU
>  
>  config GET_FREE_REGION
> -	depends on SPARSEMEM
>  	bool
>  
>  config DEVICE_PRIVATE
> -- 
> 2.39.2
>