Re: [RFC PATCH 00/12] Introduce sv48 support without relocable kernel

[Alex Ghiti <alex@ghiti.fr>]

Hi Palmer,

On 1/4/21 2:58 PM, Alexandre Ghiti wrote:
> This patchset, contrary to the previous versions, 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 is an RFC because I need to at least rebase a few commits and add
> documentation. The most interesting patches where I expect feedbacks are
> 1/12, 2/12 and 8/12. Note that moving the kernel out of the linear
> mapping and sv48 support can be separate patchsets, I share them together
> today to show that it works (this patchset is rebased on top of v5.10).
> 
> If we agree about the overall idea, I'll rebase my relocatable patchset
> on top of that and then KASLR implementation from Zong will be greatly
> simplified since moving the kernel out of the linear mapping will avoid
> to copy the kernel physically.
>                                                                                   
> 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.
>                                                                                   
> 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.
> 
> Alexandre Ghiti (12):
>    riscv: Move kernel mapping outside of linear mapping
>    riscv: Protect the kernel linear mapping
>    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
>    asm-generic: Prepare for riscv use of pud_alloc_one and pud_free
>    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
>    riscv: Improve virtual kernel memory layout dump
> 
>   arch/riscv/Kconfig                      |  34 +--
>   arch/riscv/boot/loader.lds.S            |   3 +-
>   arch/riscv/include/asm/csr.h            |   3 +-
>   arch/riscv/include/asm/fixmap.h         |   3 +
>   arch/riscv/include/asm/page.h           |  33 ++-
>   arch/riscv/include/asm/pgalloc.h        |  40 +++
>   arch/riscv/include/asm/pgtable-64.h     | 104 ++++++-
>   arch/riscv/include/asm/pgtable.h        |  68 +++--
>   arch/riscv/include/asm/sparsemem.h      |   6 +-
>   arch/riscv/kernel/cpu.c                 |  23 +-
>   arch/riscv/kernel/head.S                |   6 +-
>   arch/riscv/kernel/module.c              |   4 +-
>   arch/riscv/kernel/vmlinux.lds.S         |   3 +-
>   arch/riscv/mm/context.c                 |   2 +-
>   arch/riscv/mm/init.c                    | 376 ++++++++++++++++++++----
>   arch/riscv/mm/physaddr.c                |   2 +-
>   arch/riscv/mm/ptdump.c                  |  56 +++-
>   drivers/firmware/efi/libstub/efi-stub.c |   2 +-
>   include/asm-generic/pgalloc.h           |  24 +-
>   include/linux/sizes.h                   |   3 +-
>   20 files changed, 648 insertions(+), 147 deletions(-)
> 

Any thought about the idea ? Is it going in the right direction ? I have 
fixed quite a few things since I posted this so don't bother giving this 
patchset a full review.

Thanks,

Alex