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Re: [for 4.22 v5 01/18] xen/riscv: detect and initialize G-stage mode
- To: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 18 Nov 2025 10:05:21 +0100
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- Cc: Alistair Francis <alistair.francis@xxxxxxx>, Bob Eshleman <bobbyeshleman@xxxxxxxxx>, Connor Davis <connojdavis@xxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 18 Nov 2025 09:05:30 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 18.11.2025 09:56, Oleksii Kurochko wrote:
> On 11/13/25 5:32 PM, Jan Beulich wrote:
>> On 13.11.2025 17:18, Oleksii Kurochko wrote:
>>> Also, I’d like to note that it probably doesn’t make much sense to record
>>> all
>>> supported modes. If we traverse the|modes[]| array in the opposite
>>> order—checking
>>> |Sv57| first—then, according to the RISC-V specification:
>>> - Implementations that support Sv57 must also support Sv48.
>>> - Implementations that support Sv48 must also support Sv39.
>>> So if Sv57 is supported then lower modes are supported too. (except Sv32
>>> for RV32)
>>>
>>> Based on this, it seems reasonable to start checking from Sv57, right?
>> No. Bigger guests want running in 48x4, huge ones in 57x4 (each: if
>> available),
>> and most ones in 39x4. It doesn't matter what direction you do the checks,
>> you
>> want to know what you have available.
>
> My point was that if we change the direction, then once we find the first
> (largest)
> supported MMU mode, there is no need to check the others (lower modes) as
> according
> to the RISC-V specification, the lower modes must be supported automatically.
Oh, I see, makes sense.
Jan
|
