Re: [PATCH v5 17/26] xen/riscv: introduce minimal virtual APLIC (vAPLIC) infrastructure

[Jan Beulich <jbeulich@xxxxxxxx>]

On 13.07.2026 11:57, Oleksii Kurochko wrote:
> 
> 
> On 7/13/26 8:41 AM, Jan Beulich wrote:
>> On 10.07.2026 17:52, Oleksii Kurochko wrote:
>>> On 7/9/26 5:39 PM, Jan Beulich wrote:
>>>> On 06.07.2026 17:57, Oleksii Kurochko wrote:
>>>>> At the current development stage, only domain vINTC init and deinit
>>>>> operations are required, so implement those first.
>>>>>
>>>>> Initialize vAPLIC's domaincfg to with the interrupt-enable bit set and
>>>>> MSI delivery mode selected as the current solution is exepcted to have
>>>>> always IMSIC, and initialize vintc->ops.
>>>>
>>>> How would domaincfg be initialized on real hardware?
>>>
>>> Xen will initialize that in aplic_init_hw_interrupts():
>>> writel(APLIC_DOMAINCFG_IE | APLIC_DOMAINCFG_DM, &aplic.regs->domaincfg);
>>
>> I.e. it is very much something the OS should do.
>>
>>> I can see that maybe
>>>> firmware would have to set DM suitably (and you may mean to take firmware's
>>>> role here).
>>>
>>> I don't think that firmware will do that (and OpenSBI for example
>>> doesn't do that). If firmware can do that we for sure want to control in
>>> Xen what is written to ->domaincfg.
>>>
>>>> But isn't setting at least IE entirely the OSes responsibility?
>>>
>>> At least, Linux setups ->domaincfg once at the boot time:
>>>
>>>     /* Setup APLIC domaincfg register */
>>>     val = readl(priv->regs + APLIC_DOMAINCFG);
>>>     val |= APLIC_DOMAINCFG_IE;
>>>     if (msi_mode)
>>>             val |= APLIC_DOMAINCFG_DM;
>>>     writel(val, priv->regs + APLIC_DOMAINCFG);
>>>     if (readl(priv->regs + APLIC_DOMAINCFG) != val)
>>>             dev_warn(priv->dev, "unable to write 0x%x in domaincfg\n", val);
>>>
>>> And don't touch this register anymore, even for interrupt disablement it
>>> isn't used.
>>>
>>> So Xen can just does once:
>>> writel(APLIC_DOMAINCFG_IE | APLIC_DOMAINCFG_DM, &aplic.regs->domaincfg);
>>>
>>> and then just properly handle access of a guest to domaincfg.
>>
>> Xen can do this for itself, sure. But shouldn't domaincfg as seen by guests
>> start out 0 then?
> 
> Now I think I understand your point.
> 
> I agree that it should start from 0 (or from 0x80000000, since bits 
> 31:24 are read-only and fixed to 0x80). All other bits should be set or 
> cleared by the guest and written to vaplic->regs.domaincfg when the 
> guest accesses the vAPLIC domaincfg register.
> 
> In that case, domain_vaplic_init() should initialize ->domaincfg as:
>    vaplic->regs.domaincfg = APLIC_DOMAINCFG_RO;
> 
> instead of:
>    vaplic->regs.domaincfg = APLIC_DOMAINCFG_IE | APLIC_DOMAINCFG_DM |
>                           APLIC_DOMAINCFG_RO;

Yes.

Jan