linux-kernel - Re: [PATCH v9 05/12] mm: HUGE

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Date:   Sun, 24 Jan 2021 17:43:43 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Ding Tianhong <dingtianhong@...wei.com>, linux-mm@...ck.org
Cc:     Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Christoph Hellwig <hch@...radead.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Jonathan
 Cameron 
        <Jonathan.Cameron@...wei.com>, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, Zefan Li <lizefan@...wei.com>,
        Ingo Molnar <mingo@...hat.com>,
        Rick
 Edgecombe <rick.p.edgecombe@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>, x86@...nel.org
Subject: Re: [PATCH v9 05/12] mm: HUGE_VMAP arch support cleanup

Excerpts from Ding Tianhong's message of January 4, 2021 10:33 pm:
> On 2020/12/5 14:57, Nicholas Piggin wrote:
>> This changes the awkward approach where architectures provide init
>> functions to determine which levels they can provide large mappings for,
>> to one where the arch is queried for each call.
>> 
>> This removes code and indirection, and allows constant-folding of dead
>> code for unsupported levels.
>> 
>> This also adds a prot argument to the arch query. This is unused
>> currently but could help with some architectures (e.g., some powerpc
>> processors can't map uncacheable memory with large pages).
>> 
>> Cc: linuxppc-dev@...ts.ozlabs.org
>> Cc: Catalin Marinas <catalin.marinas@....com>
>> Cc: Will Deacon <will@...nel.org>
>> Cc: linux-arm-kernel@...ts.infradead.org
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: Ingo Molnar <mingo@...hat.com>
>> Cc: Borislav Petkov <bp@...en8.de>
>> Cc: x86@...nel.org
>> Cc: "H. Peter Anvin" <hpa@...or.com>
>> Acked-by: Catalin Marinas <catalin.marinas@....com> [arm64]
>> Signed-off-by: Nicholas Piggin <npiggin@...il.com>
>> ---
>>  arch/arm64/include/asm/vmalloc.h         |  8 +++
>>  arch/arm64/mm/mmu.c                      | 10 +--
>>  arch/powerpc/include/asm/vmalloc.h       |  8 +++
>>  arch/powerpc/mm/book3s64/radix_pgtable.c |  8 +--
>>  arch/x86/include/asm/vmalloc.h           |  7 ++
>>  arch/x86/mm/ioremap.c                    | 10 +--
>>  include/linux/io.h                       |  9 ---
>>  include/linux/vmalloc.h                  |  6 ++
>>  init/main.c                              |  1 -
>>  mm/ioremap.c                             | 88 +++++++++---------------
>>  10 files changed, 77 insertions(+), 78 deletions(-)
>> 
>> diff --git a/arch/arm64/include/asm/vmalloc.h b/arch/arm64/include/asm/vmalloc.h
>> index 2ca708ab9b20..597b40405319 100644
>> --- a/arch/arm64/include/asm/vmalloc.h
>> +++ b/arch/arm64/include/asm/vmalloc.h
>> @@ -1,4 +1,12 @@
>>  #ifndef _ASM_ARM64_VMALLOC_H
>>  #define _ASM_ARM64_VMALLOC_H
>>  
>> +#include <asm/page.h>
>> +
>> +#ifdef CONFIG_HAVE_ARCH_HUGE_VMAP
>> +bool arch_vmap_p4d_supported(pgprot_t prot);
>> +bool arch_vmap_pud_supported(pgprot_t prot);
>> +bool arch_vmap_pmd_supported(pgprot_t prot);
>> +#endif
>> +
>>  #endif /* _ASM_ARM64_VMALLOC_H */
>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index ca692a815731..1b60079c1cef 100644
>> --- a/arch/arm64/mm/mmu.c
>> +++ b/arch/arm64/mm/mmu.c
>> @@ -1315,12 +1315,12 @@ void *__init fixmap_remap_fdt(phys_addr_t dt_phys, int *size, pgprot_t prot)
>>  	return dt_virt;
>>  }
>>  
>> -int __init arch_ioremap_p4d_supported(void)
>> +bool arch_vmap_p4d_supported(pgprot_t prot)
>>  {
>> -	return 0;
>> +	return false;
>>  }
>>  
> 
> I think you should put this function in the CONFIG_HAVE_ARCH_HUGE_VMAP, otherwise it may break the compile when disable the CONFIG_HAVE_ARCH_HUGE_VMAP, the same
> as the x86 and ppc.

Ah, good catch. arm64 is okay because it always selects 
HAVE_ARCH_HUGE_VMAP, powerpc is okay because it places
them in a file that's only compiled for configs that select
huge vmap, but x86-32 without PAE build breaks. I'll fix that.

Thanks,
Nick