linux-kernel - Re: [PATCH v2 0/8] Introduce sv48 support

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Date:   Thu, 18 Jun 2020 01:37:14 -0400
From:   Alex Ghiti <alex@...ti.fr>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Zong Li <zong.li@...ive.com>, Anup Patel <anup@...infault.org>,
        Christoph Hellwig <hch@....de>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/8] Introduce sv48 support

Hi Palmer,

Le 6/3/20 à 4:10 AM, Alexandre Ghiti a écrit :
> This patchset implements sv48 support at runtime. The kernel will try to
> boot with 4-level page table and will fallback to 3-level if the HW does not
> support it.
>                                                                                   
> The biggest advantage is that we only have one kernel for 64bit, which
> is way easier to maintain.
>                                                                                   
> Folding the 4th level into a 3-level page table has almost no cost at
> runtime. But as mentioned Palmer, the relocatable code generated is less
> performant.
>                                                                                   
> At the moment, there is no way to build a 3-level page table non-relocatable
> 64bit kernel. We agreed that distributions will use this runtime configuration
> anyway, but Palmer proposed to introduce a new Kconfig, which I will do later
> as sv48 support was asked for 5.8.
>                                                                                   
> Finally, the user can now ask for sv39 explicitly by using the device-tree
> which will reduce memory footprint and reduce the number of memory accesses
> in case of TLB miss.
>
> Changes in v2:
>    * Move variable declarations to pgtable.h in patch 5/7 as suggested by Anup
>    * Restore mmu-type properties in patch 6 as suggested by Anup
>    * Fix unused variable in patch 5 that was used in patch 6
>    * Fix SPARSEMEM build (patch 2 was modified so I dropped the Reviewed-by)
>    * Applied various Reviewed-by
>
> Alexandre Ghiti (8):
>    riscv: Get rid of compile time logic with MAX_EARLY_MAPPING_SIZE
>    riscv: Allow to dynamically define VA_BITS
>    riscv: Simplify MAXPHYSMEM config
>    riscv: Prepare ptdump for vm layout dynamic addresses
>    riscv: Implement sv48 support
>    riscv: Allow user to downgrade to sv39 when hw supports sv48
>    riscv: Use pgtable_l4_enabled to output mmu type in cpuinfo
>    riscv: Explicit comment about user virtual address space size
>
>   arch/riscv/Kconfig                  |  34 ++---
>   arch/riscv/include/asm/csr.h        |   3 +-
>   arch/riscv/include/asm/fixmap.h     |   1 +
>   arch/riscv/include/asm/page.h       |  15 +++
>   arch/riscv/include/asm/pgalloc.h    |  36 ++++++
>   arch/riscv/include/asm/pgtable-64.h |  97 +++++++++++++-
>   arch/riscv/include/asm/pgtable.h    |  31 ++++-
>   arch/riscv/include/asm/sparsemem.h  |   6 +-
>   arch/riscv/kernel/cpu.c             |  23 ++--
>   arch/riscv/kernel/head.S            |   3 +-
>   arch/riscv/mm/context.c             |   2 +-
>   arch/riscv/mm/init.c                | 194 ++++++++++++++++++++++++----
>   arch/riscv/mm/ptdump.c              |  49 +++++--
>   13 files changed, 412 insertions(+), 82 deletions(-)
>

Do you any remark regarding this patchset and the others ?

Thanks,

Alex