Re: [PATCH v7 3/4] xen/riscv: panic if the device tree advertises neither Svade nor Svadu

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 10/16/26 5:34 PM, Baptiste Le Duc wrote:
> p2m_set_pte_flags() presets the A/D bits of G-stage PTEs only when
> RISCV_ISA_EXT_svade is set, which is correct only if the device tree is.
>
> The privileged spec allows exactly two schemes for updating the PTE A and D
> bits: hardware sets them on access and on write, or accessing a page whose
> A and/or D bit is clear raises a page fault so that software can set them
> (ratified as Svade). Every implementation uses one of them, but platforms
> designed before Svade and Svadu were ratified, such as the HiFive Premier
> P550, may advertise neither. Xen then cannot tell which scheme is in
> effect, so rather than guess, panic in riscv_fill_hwcap() when the device
> tree advertises neither Svade nor Svadu, so that the device tree gets
> fixed.
>
> Add Svadu to the known ISA extensions so it can be told apart from Svade.
> The comment above the enum asks for new extensions to go at the bottom to
> avoid shuffling, a leftover from Linux where the IDs were macros with
> explicit values. Nothing depends on the enum values, so have the comment
> say that multi-letter extensions follow the order of riscv_isa_ext[].
>
> Suggested-by: Jan Beulich <jbeulich@xxxxxxxx>
> Assisted-by: Claude:claude-opus-5-5
> Signed-off-by: Baptiste Le Duc <baptiste.le-duc@xxxxxxxxxx>
Reviewed-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>

~ Oleksii