linux-kernel - Re: [RFC PATCH v2 14/32] x86: mm: Provide support to use memblock when spliting large pages

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Message-ID: <c3b12452-9533-87c8-4543-8f12f5c90fe3@redhat.com>
Date:   Thu, 16 Mar 2017 14:15:19 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Brijesh Singh <brijesh.singh@....com>, Borislav Petkov <bp@...e.de>
Cc:     simon.guinot@...uanux.org, linux-efi@...r.kernel.org,
        kvm@...r.kernel.org, rkrcmar@...hat.com, matt@...eblueprint.co.uk,
        linux-pci@...r.kernel.org, linus.walleij@...aro.org,
        gary.hook@....com, linux-mm@...ck.org,
        paul.gortmaker@...driver.com, hpa@...or.com, cl@...ux.com,
        dan.j.williams@...el.com, aarcange@...hat.com,
        sfr@...b.auug.org.au, andriy.shevchenko@...ux.intel.com,
        herbert@...dor.apana.org.au, bhe@...hat.com, xemul@...allels.com,
        joro@...tes.org, x86@...nel.org, peterz@...radead.org,
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        akpm@...ux-foundation.org, davem@...emloft.net
Subject: Re: [RFC PATCH v2 14/32] x86: mm: Provide support to use memblock
 when spliting large pages



On 10/03/2017 23:41, Brijesh Singh wrote:
>> Maybe there's a reason this fires:
>>
>> WARNING: modpost: Found 2 section mismatch(es).
>> To see full details build your kernel with:
>> 'make CONFIG_DEBUG_SECTION_MISMATCH=y'
>>
>> WARNING: vmlinux.o(.text+0x48edc): Section mismatch in reference from
>> the function __change_page_attr() to the function
>> .init.text:memblock_alloc()
>> The function __change_page_attr() references
>> the function __init memblock_alloc().
>> This is often because __change_page_attr lacks a __init
>> annotation or the annotation of memblock_alloc is wrong.
>>
>> WARNING: vmlinux.o(.text+0x491d1): Section mismatch in reference from
>> the function __change_page_attr() to the function
>> .meminit.text:memblock_free()
>> The function __change_page_attr() references
>> the function __meminit memblock_free().
>> This is often because __change_page_attr lacks a __meminit
>> annotation or the annotation of memblock_free is wrong.
>> 
>> But maybe Paolo might have an even better idea...
> 
> I am sure he will have better idea :)

Not sure if it's better or worse, but an alternative idea is to turn
__change_page_attr and __change_page_attr_set_clr inside out, so that:
1) the alloc_pages/__free_page happens in __change_page_attr_set_clr;
2) __change_page_attr_set_clr overall does not beocome more complex.

Then you can introduce __early_change_page_attr_set_clr and/or
early_kernel_map_pages_in_pgd, for use in your next patches.  They use
the memblock allocator instead of alloc/free_page

The attached patch is compile-tested only and almost certainly has some
thinko in it.  But it even skims a few lines from the code so the idea
might have some merit.

Paolo

View attachment "alloc-in-cpa-set-clr.patch" of type "text/x-patch" (9875 bytes)