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Date:   Wed, 19 Jan 2022 20:18:10 -0800 (PST)
Subject:     Re: [PATCH v3 00/13] Introduce sv48 support without relocatable kernel
In-Reply-To: <20211206104657.433304-1-alexandre.ghiti@canonical.com>
CC:     corbet@lwn.net, Paul Walmsley <paul.walmsley@sifive.com>,
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        dvyukov@google.com, ardb@kernel.org, Arnd Bergmann <arnd@arndb.de>,
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        panqinglin2020@iscas.ac.cn, linux-doc@vger.kernel.org,
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        kasan-dev@googlegroups.com, linux-efi@vger.kernel.org,
        linux-arch@vger.kernel.org, alexandre.ghiti@canonical.com
From:   Palmer Dabbelt <palmer@dabbelt.com>
To:     alexandre.ghiti@canonical.com
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On Mon, 06 Dec 2021 02:46:44 PST (-0800), alexandre.ghiti@canonical.com wrote:
> * Please note notable changes in memory layouts and kasan population *
>
> This patchset allows to have a single kernel for sv39 and sv48 without
> being relocatable.
>
> The idea comes from Arnd Bergmann who suggested to do the same as x86,
> that is mapping the kernel to the end of the address space, which allows
> the kernel to be linked at the same address for both sv39 and sv48 and
> then does not require to be relocated at runtime.
>
> This 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. Folding the 4th level into a 3-level page table has almost no
> cost at runtime.
>
> Note that kasan region had to be moved to the end of the address space
> since its location must be known at compile-time and then be valid for
> both sv39 and sv48 (and sv57 that is coming).
>
> Tested on:
>   - qemu rv64 sv39: OK
>   - qemu rv64 sv48: OK
>   - qemu rv64 sv39 + kasan: OK
>   - qemu rv64 sv48 + kasan: OK
>   - qemu rv32: OK
>
> Changes in v3:
>   - Fix SZ_1T, thanks to Atish
>   - Fix warning create_pud_mapping, thanks to Atish
>   - Fix k210 nommu build, thanks to Atish
>   - Fix wrong rebase as noted by Samuel
>   - * Downgrade to sv39 is only possible if !KASAN (see commit changelog) *
>   - * Move KASAN next to the kernel: virtual layouts changed and kasan population *
>
> Changes in v2:
>   - Rebase onto for-next
>   - Fix KASAN
>   - Fix stack canary
>   - Get completely rid of MAXPHYSMEM configs
>   - Add documentation
>
> Alexandre Ghiti (13):
>   riscv: Move KASAN mapping next to the kernel mapping
>   riscv: Split early kasan mapping to prepare sv48 introduction
>   riscv: Introduce functions to switch pt_ops
>   riscv: Allow to dynamically define VA_BITS
>   riscv: Get rid of MAXPHYSMEM configs
>   asm-generic: Prepare for riscv use of pud_alloc_one and pud_free
>   riscv: Implement sv48 support
>   riscv: Use pgtable_l4_enabled to output mmu_type in cpuinfo
>   riscv: Explicit comment about user virtual address space size
>   riscv: Improve virtual kernel memory layout dump
>   Documentation: riscv: Add sv48 description to VM layout
>   riscv: Initialize thread pointer before calling C functions
>   riscv: Allow user to downgrade to sv39 when hw supports sv48 if !KASAN
>
>  Documentation/riscv/vm-layout.rst             |  48 ++-
>  arch/riscv/Kconfig                            |  37 +-
>  arch/riscv/configs/nommu_k210_defconfig       |   1 -
>  .../riscv/configs/nommu_k210_sdcard_defconfig |   1 -
>  arch/riscv/configs/nommu_virt_defconfig       |   1 -
>  arch/riscv/include/asm/csr.h                  |   3 +-
>  arch/riscv/include/asm/fixmap.h               |   1
>  arch/riscv/include/asm/kasan.h                |  11 +-
>  arch/riscv/include/asm/page.h                 |  20 +-
>  arch/riscv/include/asm/pgalloc.h              |  40 ++
>  arch/riscv/include/asm/pgtable-64.h           | 108 ++++-
>  arch/riscv/include/asm/pgtable.h              |  47 +-
>  arch/riscv/include/asm/sparsemem.h            |   6 +-
>  arch/riscv/kernel/cpu.c                       |  23 +-
>  arch/riscv/kernel/head.S                      |   4 +-
>  arch/riscv/mm/context.c                       |   4 +-
>  arch/riscv/mm/init.c                          | 408 ++++++++++++++----
>  arch/riscv/mm/kasan_init.c                    | 250 ++++++++---
>  drivers/firmware/efi/libstub/efi-stub.c       |   2
>  drivers/pci/controller/pci-xgene.c            |   2 +-
>  include/asm-generic/pgalloc.h                 |  24 +-
>  include/linux/sizes.h                         |   1
>  22 files changed, 833 insertions(+), 209 deletions(-)

Sorry this took a while.  This is on for-next, with a bit of juggling: a 
handful of trivial fixes for configs that were failing to build/boot and 
some merge issues.  I also pulled out that MAXPHYSMEM fix to the top, so 
it'd be easier to backport.  This is bigger than something I'd normally like to
take late in the cycle, but given there's a lot of cleanups, likely some fixes,
and it looks like folks have been testing this I'm just going to go with it.

Let me know if there's any issues with the merge, it was a bit hairy.  
Probably best to just send along a fixup patch at this point.

Thanks!