Re: [PATCH v2 6/8] xen/riscv: introduce generic Xen page table handling

[Julien Grall <julien@xxxxxxx>]

Hi,

On 12/07/2024 17:22, Oleksii Kurochko wrote:
> At least, between Arm and RISC-V most of the code related to Xen page
> table handling are common.
>
> This GENERIC_PT code is based on Arm's arm/mmu/pt.c except some minor
> changes such as introduction of the following functions:
>    * get_root_page()
>    * xen_pt_check_contig()
>    * set_pte_table_bit()
>    * sanity_arch_specific_pte_checks()
>    * get_contig_bit()
>    * set_pte_permissions()
>    * flush_xen_tlb_range_va()
> It was done because not every functions has the generic pte_flags and
> it could be a different positions of the PTE bits in a PTE.
While I am always in favor of trying to avoid code duplication, I am not 
sure the page-tables are one that should be.
For instance, you don't have the concept of contiguous page in RISC-V (I 
see you introduce dummy flags, but IMHO this is a bit of a hack). All 
the code was also written in a way to avoid temporary conflict mappings. 
This is to avoid using Break-Before-Make. But on newer hardware this 
could be relaxed.
I am interested to know what the others thinks.

Cheers,

--
Julien Grall