Re: [PATCH v5 08/11] xen/riscv: rework G-stage mode handling

[Jan Beulich <jbeulich@xxxxxxxx>]

On 07.05.2026 10:58, Oleksii Kurochko wrote:
> Rework G-stage mode handling to make the selected mode descriptor
> reusable outside of p2m initialization, both for filling CPU nodes in
> the device tree passed to dom0less guests and for per-domain G-stage
> mode selection at domain creation time.
> 
> Promote gstage_modes[] from a local __initconst variable inside
> gstage_mode_detect() to a file-scope static const array, and convert
> max_gstage_mode from an embedded struct (assigned by value) to a global
> const pointer into gstage_modes[]. This allows referencing both the mode
> identifier and the mode name after init without copying the descriptor.
> Remove get_max_supported_mode(); its callers now dereference
> max_gstage_mode->mode directly.
> 
> Change struct p2m_domain::mode from an embedded gstage_mode_desc to a
> const pointer into gstage_modes[], so each domain shares the descriptor
> rather than carrying its own copy.
> 
> Adjust the gstage_modes[] entries in three ways:
>  - Use lowercase names without the "x4" suffix (e.g. "sv39" instead of
>    "Sv39x4"). The DT mmu-type binding [1] does not include the suffix,
>    so the name can now be passed directly to the guest without
>    transformation. The suffix is appended only in the diagnostic
>    printk, where it remains informative.
>  - Use "none" for Bare mode (HGATP_MODE_OFF) to match the DT binding.
>  - Change paging_levels to represent the root page-table level index
>    (i.e. total paging levels minus one) rather than the total count.
>    P2M_ROOT_LEVEL() now returns the correct VPN index directly, without
>    requiring callers to subtract one or use hardcoded offsets.
> 
> Add gstage_mode to xen_arch_domainconfig so the toolstack can
> request a specific G-stage mode at domain creation time. Introduce
> find_gstage_mode() to resolve a mode descriptor by HGATP_MODE_*,
> capping the result at max_gstage_mode to prevent requesting a mode
> the hardware does not support. Update p2m_init() to accept a
> xen_domctl_createdomain pointer and call find_gstage_mode()
> instead of hardcoding Sv39x4.
> 
> Add arch_parse_dom0less_node() in a new dom0less-build.c to read the
> "mmu-type" DT property from a guest domain node and store it in
> boot_domain::create_cfg.arch.gstage_mode, falling back to maximum
> supported mode when the property is absent.
> 
> [1] 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/riscv/cpus.yaml?h=v6.19-rc3#n82
> 
> Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>

Acked-by: Jan Beulich <jbeulich@xxxxxxxx>