linux-kernel - Re: [PATCH v4 2/2] RISC-V: Implement sparsemem

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Message-ID: <0d81412d-73fc-fa56-6f84-dedda72b9cc6@deltatee.com>
Date:   Wed, 14 Aug 2019 10:56:35 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Greentime Hu <green.hu@...il.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Rob Herring <robh@...nel.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Andrew Waterman <andrew@...ive.com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Stephen Bates <sbates@...thlin.com>,
        Olof Johansson <olof@...om.net>, greentime.hu@...ive.com,
        linux-riscv@...ts.infradead.org,
        Michael Clark <michaeljclark@....com>,
        Christoph Hellwig <hch@....de>, linux-mm@...r.kernel.org
Subject: Re: [PATCH v4 2/2] RISC-V: Implement sparsemem



On 2019-08-14 7:35 a.m., Greentime Hu wrote:
> Logan Gunthorpe <logang@...tatee.com> 於 2019年8月14日 週三 上午12:50寫道：
>>
>> On 2019-08-13 10:39 a.m., Paul Walmsley wrote:
>>> On Tue, 13 Aug 2019, Logan Gunthorpe wrote:
>>>
>>>> On 2019-08-13 12:04 a.m., Greentime Hu wrote:
>>>>
>>>>> Every architecture with mmu defines their own pfn_valid().
>>>>
>>>> Not true. Arm64, for example just uses the generic implementation in
>>>> mmzone.h.
>>>
>>> arm64 seems to define their own:
>>>
>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/Kconfig#n899
>>
>> Oh, yup. My mistake.
>>
>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/mm/init.c#n235
>>>
>>> While there are many architectures which have their own pfn_valid();
>>> oddly, almost none of them set HAVE_ARCH_PFN_VALID ?
>>
>> Yes, much of this is super confusing. Seems HAVE_ARCH_PFN_VALID only
>> matters if SPARSEMEM is set. So risc-v probably doesn't need to set it
>> and we just need a #ifdef !CONFIG_FLATMEM around the pfn_valid
>> definition like other arches.
>>
> 
> Maybe this commit explains why it used HAVE_ARCH_PFN_VALID instead of SPARSEMEM.
> https://github.com/torvalds/linux/commit/7b7bf499f79de3f6c85a340c8453a78789523f85
> 
> BTW, I found another issue here.
> #define FIXADDR_TOP            (VMALLOC_START)
> #define FIXADDR_START           (FIXADDR_TOP - FIXADDR_SIZE)
> #define VMEMMAP_END    (VMALLOC_START - 1)
> #define VMEMMAP_START  (VMALLOC_START - VMEMMAP_SIZE)
> These 2 regions are overlapped.
> 
> How about this fix? Not sure if it is good for everyone.

Yes, this looks good to me. I can fold these changes into my patch and
send a v5 to the list.

Thanks!

Logan


> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 3f12b069af1d..3c4d394679d0 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -115,9 +115,6 @@ config PGTABLE_LEVELS
>         default 3 if 64BIT
>         default 2
> 
> -config HAVE_ARCH_PFN_VALID
> -       def_bool y
> -
>  menu "Platform type"
> 
>  choice
> diff --git a/arch/riscv/include/asm/fixmap.h b/arch/riscv/include/asm/fixmap.h
> index c207f6634b91..72e106b60bc5 100644
> --- a/arch/riscv/include/asm/fixmap.h
> +++ b/arch/riscv/include/asm/fixmap.h
> @@ -26,7 +26,7 @@ enum fixed_addresses {
>  };
> 
>  #define FIXADDR_SIZE           (__end_of_fixed_addresses * PAGE_SIZE)
> -#define FIXADDR_TOP            (VMALLOC_START)
> +#define FIXADDR_TOP            (VMEMMAP_START)
>  #define FIXADDR_START          (FIXADDR_TOP - FIXADDR_SIZE)
> 
>  #define FIXMAP_PAGE_IO         PAGE_KERNEL
> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> index 8ddb6c7fedac..83830997dce6 100644
> --- a/arch/riscv/include/asm/page.h
> +++ b/arch/riscv/include/asm/page.h
> @@ -100,8 +100,10 @@ extern unsigned long min_low_pfn;
>  #define page_to_bus(page)      (page_to_phys(page))
>  #define phys_to_page(paddr)    (pfn_to_page(phys_to_pfn(paddr)))
> 
> +#if defined(CONFIG_FLATMEM)
>  #define pfn_valid(pfn) \
>         (((pfn) >= pfn_base) && (((pfn)-pfn_base) < max_mapnr))
> +#endif
> 
>  #define ARCH_PFN_OFFSET                (pfn_base)