Re: [XEN PATCH v10 5/5] domctl: Add XEN_DOMCTL_gsi_permission to grant gsi

[Jan Beulich <jbeulich@xxxxxxxx>]

On 20.06.2024 11:40, Chen, Jiqian wrote:
> On 2024/6/18 17:23, Jan Beulich wrote:
>> On 18.06.2024 10:23, Chen, Jiqian wrote:
>>> On 2024/6/17 23:32, Jan Beulich wrote:
>>>> On 17.06.2024 11:00, Jiqian Chen wrote:
>>>>> @@ -1516,14 +1519,39 @@ static void pci_add_dm_done(libxl__egc *egc,
>>>>>              rc = ERROR_FAIL;
>>>>>              goto out;
>>>>>          }
>>>>> -        r = xc_domain_irq_permission(ctx->xch, domid, irq, 1);
>>>>> +#ifdef CONFIG_X86
>>>>> +        /* If dom0 doesn't have PIRQs, need to use 
>>>>> xc_domain_gsi_permission */
>>>>> +        r = xc_domain_getinfo_single(ctx->xch, 0, &info);
>>>>
>>>> Hard-coded 0 is imposing limitations. Ideally you would use DOMID_SELF, but
>>>> I didn't check if that can be used with the underlying hypercall(s). 
>>>> Otherwise
> From the commit 10ef7a91b5a8cb8c58903c60e2dd16ed490b3bcf, DOMID_SELF is not 
> allowed for XEN_DOMCTL_getdomaininfo.
> And now XEN_DOMCTL_getdomaininfo gets domain through rcu_lock_domain_by_id.
> 
>>>> you want to pass the actual domid of the local domain here.
> What is the local domain here?

The domain your code is running in.

> What is method for me to get its domid?

I hope there's an available function in one of the libraries to do that.
But I wouldn't even know what to look for; that's a question to (primarily)
Anthony then, who sadly continues to be our only tool stack maintainer.

Alternatively we could maybe enable XEN_DOMCTL_getdomaininfo to permit
DOMID_SELF.

>>> But the action of granting permission is from dom0 to domU, what I need to 
>>> get is the infomation of dom0,
>>> The actual domid here is domU's id I think, it is not useful.
>>
>> Note how I said DOMID_SELF and "local domain". There's no talk of using the
>> DomU's domid. But what you apparently neglect is the fact that the hardware
>> domain isn't necessarily Dom0 (see CONFIG_LATE_HWDOM in the hypervisor).
>> While benign in most cases, this is relevant when it comes to referencing
>> the hardware domain by domid. And it is the hardware domain which is going
>> to drive the device re-assignment, as that domain is who's in possession of
>> all the devices not yet assigned to any DomU.
> OK, I need to get the information of hardware domain here?

Right, with (for this purpose) "hardware domain" == "local domain".

Jan