Re: [PATCH v1 06/17] xen/riscv: map IMSIC interrupt file for vCPUs

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

On 8/13/26 11:49 AM, Baptiste Le Duc wrote:
> On 2026-08-13 11:42 +0200, Oleksii Kurochko wrote:
>>>> +/*
>>>> + * Map the physical IMSIC guest interrupt file (G-file) assigned to vCPU v
>>> Nit: What is this `v`?
>>
>> A function argument. But I will just drop v from the comment.
>>
>>>> + * into the domain's stage-2 guest-physical address space.
>>>> + *
>>>> + * In the machine's physical address space (SPA), each hart's IMSIC
>>>> + * supervisor-level file (S-file) is located at offset 0 of its address block,
>>>> + * followed contiguously by GEILEN guest files at offsets of 1, 2, ..., N pages.
>>>> + *
>>>> + * Because a guest OS running in VS-mode expects its own supervisor-level
>>>> + * interrupt file to be at offset 0 of its guest-physical IMSIC block, the
>>>> + * hypervisor must use stage-2 address translation to map the vCPU's
>>>> + * guest-physical "supervisor" page (GPA offset 0) to the specific
>>>> + * physical guest file page (SPA offset guest_file_id) on the physical hart.
>>>> + *
>>>> + * Xen pins each vCPU to a pCPU (v->processor) and assigns it a physical
>>>
>>>
>>>> + * guest file index (guest_file_id) from the vGEIN allocator. A guest_file_id
>>>> + * of 0 indicates that no hardware guest file is selected (matching the
>>>> + * architectural behavior where vGEIN = 0 in the hstatus CSR selects no
>>>> + * guest external interrupt source), requiring the VS-file to be emulated
>>>> + * in software.
>>>> + *
>>>> + * The base guest-physical address advertised to the guest in the device
>>>> + * tree matches offset 0 of the vCPU's virtual IMSIC block. Stage-2
>>>> + * translation ensures that guest supervisor accesses to this page are
>>>> + * transparently routed to the real hardware VS-file granted to it on
>>>> + * the current pCPU.
>>>> + */
>>>> +int imsic_map_guest_file(struct vcpu *v, unsigned int vsfile_id)
>>>> +{
>>>> +    int res = 0;
>>>> +    struct domain *d = v->domain;
>>>> +    unsigned int cpu = v->processor;
>>>> +    vaddr_t gaddr = imsic_cfg.base_addr + (IMSIC_MMIO_PAGE_SZ * v->vcpu_id);
>>>
>>> The variable holds a guest-physical address, so vaddr_t is the wrong
>>> type should be either paddr_t or gaddr_t.
>>
>> Agree, paddr_t will be better what was mentioned in thread with Jan B.
>>
>>>
>>>> +    paddr_t paddr;
>>>> +    unsigned long guest_stride;
>>>> +
>>>> +    /* Nothing to map in the case of sw interrupt file. */
>>>
>>> There is no software interrupt file implementation in this series, patch 11
>>> turns the non-MSI path into a BUG_ON(). So "vsfile_id == 0" today means "this
>>> vCPU gets no external interrupts at all and nothing tells anybody". Worth
>>> saying so plainly here rather than implying a fallback exists.
>>
>> I would ask then different question will this function change when IMSIC
>> interrupt file support will be added? I think - no as in the case of
> Did you forget s/w word? If not it's weird as IMSIC interrupt file is
> the current topic of this patch series.
>> IMSIC interrupt file we don't need any stage-2 mapping. So here it is
> here too.

Yes, sorry, I missed s/w word.

>> just a check that nothing should be mapped for non-hw-assisted interrupt
>> files.
>>
>>>
>>>> +    if ( !vsfile_id )
>>>> +        return res;
>>>> +
>>>> +    guest_stride = vsfile_id * IMSIC_MMIO_PAGE_SZ;
>>>
>>>
>>>> +
>>>> +    paddr = imsic_cfg.msi[cpu].base_addr + imsic_cfg.msi[cpu].offset +
>>>> +            guest_stride;
>>>
>>>
>>>> +
>>>> +#ifdef IMSIC_DEBUG
>>>
>>>> +    printk("%s: %pv: ga(%#lx) -> pa(%#lx), cpu(%#x), guest_file_id(%d) "
>>>> +           "base_addr(%#lx) offset(%#lx)\n", __func__, v, gaddr, paddr, cpu,
>>>> +           vsfile_id, imsic_cfg.msi[cpu].base_addr, imsic_cfg.msi[cpu].offset);
>>>> +#endif
>>>> +
>>>> +    res = map_regions_p2mt(d, gaddr_to_gfn(gaddr),
>>>> +                           PFN_DOWN(IMSIC_MMIO_PAGE_SZ), maddr_to_mfn(paddr),
>>>> +                           arch_dt_passthrough_p2m_type());
>>>> +    if ( res )
>>>> +        printk("%s: Failed to map %#lx to the guest at %#lx\n",
>>>

~ Oleksii