Re: [PATCH v7 0/2] xen/riscv: introduce identity mapping

[Oleksii <oleksii.kurochko@xxxxxxxxx>]

Hello Bobby and Alistair,

Could you kindly take a moment to examine this series of patches?
Your input would be highly valued.

Thanks in advance.

~ Oleksii

On Tue, 2023-08-08 at 18:14 +0300, Oleksii Kurochko wrote:
> The patch series introduces things necessary to implement identity
> mapping:
>   1. Make identity mapping for the entire Xen.
>   2. Enable MMU.
>   3. Jump to the virtual address world
>   4. Remove identity mapping.
> 
> Also current patch series introduces the calculation of physical
> offset before
> MMU is enabled as access to physical offset will be calculated wrong
> after
> MMU will be enabled because access to phys_off variable is PC-
> relative and
> in the case when linker address != load address, it will cause MMU
> fault.
> 
> The reason for this patch series can be found here:
> https://lore.kernel.org/xen-devel/4e336121-fc0c-b007-bf7b-430352563d55@xxxxxxxxxx/
> 
> ---
> Changes in V7:
>  - use srli instruction to be consistent with slli instruction in
> turn_on_mmu()
> ---
> Changes in V6:
>   - Update calc_phys_offset() after rebase.
>   - Refactor turn_on_mmu() and a way how an argument of turn_on_mmu()
> is
>     calculated.
> ---
> Changes in V5:
>         - update the algo of identity mapping removing.
>         - introduce IDENT_AREA_SIZE.
>         - introduce turn_on_mmu() function to enable and switch from
> 1:1 mapping.
>         - fix typo in PGTBL_INITIAL_COUNT define.
>         - update the comment above PGTBL_INITIAL_COUNT.
>         - update prototype of calc_phys_offset(). now it returns
> phys_offset.
>         - declare phys_offset as static.
>         - save returned value of calc_phys_offset to register s2.
> ---
> Changes in V4:
>   - drop patch  [PATCH v3 1/3] xen/riscv: add SPDX tag to config.h as
> it was
>     merged to staging
>   - remove definition of ARRAY_SIZE and ROUNDUP as <xen/macors.h> was
> introduced where these macros are located now.
>         - update definition of PGTBL_INITIAL_COUNT
>         - update the commit message for patch 'xen/riscv: introduce
> identity mapping'
>         - update the comments in head.S
>   - update the algo of identity mapping removing 
> ---
> Changes in V3:
>  - Update the patch series message.
>  - The following patches were merged to staging so droped from the
> patch series:
>    * xen/riscv: add .sbss section to .bss
>    * xen/riscv: introduce reset_stack() function
>    * xen/riscv: move extern of cpu0_boot_stack to header
>    * xen/riscv: add SPDX tags
>  - move save/restore of a0/a1 registers from patch 4 to patch 2 (
> numbers are
>    from the previous patch series version )
>  - add SPDX tag in config.h
>  - update definition of PGTBL_INITIAL_COUNT taking into account
> identity mapping.
>  - refactor remove_identity_mapping() function.
>  - add explanatory comments in xen.lds.S and mm.c.
> ---
> Changes in V2:
>  - update the patch series message.
>  - drop patches from the previous version of the patch series:
>    * xen/riscv: add __ASSEMBLY__ guards". ( merged )
>    * xen/riscv: make sure that identity mapping isn't bigger then
> page size
>      ( entire Xen is 1:1 mapped so there is no need for the checks
> from the patch )
>  - add .sbss.* and put it befor .bss* .
>  - move out reset_stack() to .text section.
>  - add '__ro_after_init' for phys_offset variable.
>  - add '__init' for calc_phys_offset().
>  - declaring variable phys_off as non static as it will be used in
> head.S.
>  - update definition of PGTBL_INITIAL_COUNT and the comment above.
>  - code style fixes.
>  - remove id_addrs array becase entire Xen is mapped.
>  - reverse condition for cycle inside remove_identity_mapping().
>  - fix page table walk in remove_identity_mapping().
>  - save hart_id and dtb_addr before call MMU related C functions
>  - use phys_offset variable instead of doing calcultations to get
> phys offset
>    in head.S file. ( it can be easily done as entire Xen is 1:1
> mapped now )
>  - declare enable_muu() as __init.
>  - Update SPDX tags.
>  - Add Review-By/Suggested-By for some patches.
>  - code style fixes.
> 
> Oleksii Kurochko (2):
>   xen/riscv: introduce function for physical offset calculation
>   xen/riscv: introduce identity mapping
> 
>  xen/arch/riscv/include/asm/acpi.h   |   6 ++
>  xen/arch/riscv/include/asm/config.h |   2 +
>  xen/arch/riscv/include/asm/mm.h     |   7 +-
>  xen/arch/riscv/mm.c                 | 109 +++++++++++++++++---------
> --
>  xen/arch/riscv/riscv64/head.S       |  44 +++++++++++
>  xen/arch/riscv/setup.c              |  14 +---
>  xen/arch/riscv/xen.lds.S            |  11 +++
>  7 files changed, 136 insertions(+), 57 deletions(-)
>  create mode 100644 xen/arch/riscv/include/asm/acpi.h
>