Re: [PATCH v3 6/6] xen/riscv: make Zihintpause no longer a required extension

[Oleksii Kurochko <oleksii.kurochko@gmail.com>]

On 9/29/26 6:32 PM, Baptiste Le Duc wrote:
> Zihintpause is in required_extensions[] so Xen panics when it is missing,
> while it does not strictly require hardware support for it.
> 
> The PAUSE hint (Zihintpause extension) is encoded as FENCE W, 0
> (0x0100000F). In accordance with the RISC-V Unprivileged ISA, HINTs are
> encoded in the space of valid standard instructions. On platforms without
> Zihintpause support, executing 0x0100000F is treated as a standard FENCE
> with an empty successor set, which acts as a NOP and never generates an
> illegal instruction trap.
> 
> Zihintpause is therefore purely an optimization hint. Drop it from
> required_extensions[] so Xen can still boot on systems that don't advertise
> it, and print a warning in that case.
> 
> Assisted-by: Claude:claude-opus-5
> Signed-off-by: Baptiste Le Duc <baptiste.le-duc@vates.tech>
> ---
> Changes since v2:
> - rewrite commit message
> - print a warning at boot when Zihintpause is unavailable
> - drop Zihintpause requirement from booting.txt
> ---
> Changes since v1:
> - rewrite commit message.
> ---
LGTM:

Reviewed-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>

Thanks.

~ Oleksii