Re: [PATCH v3 08/14] xen/riscv: imsic_init() implementation

[Jan Beulich <jbeulich@xxxxxxxx>]

On 05.06.2025 12:15, Oleksii Kurochko wrote:
> 
> On 6/5/25 11:42 AM, Jan Beulich wrote:
>> On 05.06.2025 11:13, Oleksii Kurochko wrote:
>>> On 6/5/25 8:50 AM, Jan Beulich wrote:
>>>> On 04.06.2025 17:36, Oleksii Kurochko wrote:
>>>>> On 6/2/25 12:21 PM, Jan Beulich wrote:
>>>>>> On 26.05.2025 20:44, Oleksii Kurochko wrote:
>>>>>>> On 5/22/25 4:46 PM, Jan Beulich wrote:
>>>>>>>> On 21.05.2025 18:03, Oleksii Kurochko wrote:
>>>>>>>>> +    /* Check MMIO register sets */
>>>>>>>>> +    for ( unsigned int i = 0; i < nr_mmios; i++ )
>>>>>>>>> +    {
>>>>>>>>> +        if ( !alloc_cpumask_var(&imsic_cfg.mmios[i].cpus) )
>>>>>>>>> +        {
>>>>>>>>> +            rc = -ENOMEM;
>>>>>>>>> +            goto imsic_init_err;
>>>>>>>>> +        }
>>>>>>>>> +
>>>>>>>>> +        rc = dt_device_get_address(node, i, 
>>>>>>>>> &imsic_cfg.mmios[i].base_addr,
>>>>>>>>> +                                   &imsic_cfg.mmios[i].size);
>>>>>>>>> +        if ( rc )
>>>>>>>>> +        {
>>>>>>>>> +            printk(XENLOG_ERR "%s: unable to parse MMIO regset %u\n",
>>>>>>>>> +                   node->name, i);
>>>>>>>>> +            goto imsic_init_err;
>>>>>>>>> +        }
>>>>>>>>> +
>>>>>>>>> +        base_addr = imsic_cfg.mmios[i].base_addr;
>>>>>>>>> +        base_addr &= ~(BIT(imsic_cfg.guest_index_bits +
>>>>>>>>> +                           imsic_cfg.hart_index_bits +
>>>>>>>>> +                           IMSIC_MMIO_PAGE_SHIFT, UL) - 1);
>>>>>>>>> +        base_addr &= ~((BIT(imsic_cfg.group_index_bits, UL) - 1) <<
>>>>>>>>> +                       imsic_cfg.group_index_shift);
>>>>>>>>> +        if ( base_addr != imsic_cfg.base_addr )
>>>>>>>>> +        {
>>>>>>>>> +            rc = -EINVAL;
>>>>>>>>> +            printk(XENLOG_ERR "%s: address mismatch for regset %u\n",
>>>>>>>>> +                   node->name, i);
>>>>>>>>> +            goto imsic_init_err;
>>>>>>>>> +        }
>>>>>>>> Maybe just for my own understanding: There's no similar check for the
>>>>>>>> sizes to match / be consistent wanted / needed?
>>>>>>> If you are speaking about imsic_cfg.mmios[i].size then it depends fully 
>>>>>>> on h/w will
>>>>>>> provide, IMO.
>>>>>>> So I don't what is possible range for imsic_cfg.mmios[i].size.
>>>>>> Well, all I can say is that's it feels odd that you sanity check 
>>>>>> base_addr
>>>>>> but permit effectively any size.
>>>>> Okay, I think I have two ideas how to check the size:
>>>>> 1. Based on guest bits from IMSIC's DT node. QEMU calculates a size as:
>>>>>        for (socket = 0; socket < socket_count; socket++) {
>>>>>            imsic_addr = base_addr + socket * VIRT_IMSIC_GROUP_MAX_SIZE;
>>>>>            imsic_size = IMSIC_HART_SIZE(imsic_guest_bits) *
>>>>>                         s->soc[socket].num_harts;
>>>>>        ...
>>>>>       where:
>>>>>         #define IMSIC_MMIO_PAGE_SHIFT          12
>>>>>         #define IMSIC_MMIO_PAGE_SZ             (1UL << 
>>>>> IMSIC_MMIO_PAGE_SHIFT)
>>>>>         
>>>>>         #define IMSIC_HART_NUM_GUESTS(__guest_bits)           \
>>>>>                 (1U << (__guest_bits))
>>>>>         #define IMSIC_HART_SIZE(__guest_bits)                 \
>>>>>                 (IMSIC_HART_NUM_GUESTS(__guest_bits) * IMSIC_MMIO_PAGE_SZ)
>>>>>
>>>>> 2. Just take a theoretical maximum for S-mode IMSIC's node:
>>>>>        16,384 * 64 1(S-mode interrupt file) + 63(max guest interrupt 
>>>>> files)) * 4 KiB
>>>>>       Where,
>>>>>         16,384 - maximum possible amount of harts according to AIA spec
>>>>>         64 - a maximum amount of possible interrupt file for S-mode IMSIC 
>>>>> node:
>>>>>              1 - S interupt file + 63 guest interrupt files.
>>>>>         4 Kib - a maximum size of one interrupt file.
>>>>>
>>>>> Which option is preferred?
>>>> I would have said 2, if your outline used "actual" rather than "maximum" 
>>>> values.
>>> In option 2 maximum possible values are used. If we want to use "actual" 
>>> values then
>>> the option 1 should be used.
>> Actually I was wrong with request "actual" uniformly. It's only the hart 
>> count where
>> I meant to ask for that. For interrupts we should allow the maximum possible 
>> unless
>> we already know their count.
> 
> Do you mean 'interrupt file' here?

Yes, I do. Sorry for getting the terminology wrong.

Jan

> If yes, then an amount of them shouldn't be bigger
> then 1 + BIT(guest_bits).
> 
> ~ Oleksii
>