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

[Jan Beulich <jbeulich@xxxxxxxx>]

On 21.06.2024 10:20, Chen, Jiqian wrote:
> On 2024/6/20 18:42, Jan Beulich wrote:
>> 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.
> I didn't find relate function.
> Hi Anthony, do you know?
> 
>> 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.
> It didn't permit DOMID_SELF since below commit. Does it still have the same 
> problem if permit DOMID_SELF?

To answer this, all respective callers would need auditing. However, ...

> commit 10ef7a91b5a8cb8c58903c60e2dd16ed490b3bcf
> Author: kfraser@localhost.localdomain <kfraser@localhost.localdomain>
> Date:   Tue Aug 14 09:56:46 2007 +0100
> 
>     xen: Do not accept DOMID_SELF as input to DOMCTL_getdomaininfo.
>     This was screwing up callers that loop on getdomaininfo(), if there
>     was a domain with domid DOMID_FIRST_RESERVED-1 (== DOMID_SELF-1).
>     They would see DOMID_SELF-1, then look up DOMID_SELF, which has domid
>     0 of course, and then start their domain-finding loop all over again!
>     Found by Kouya Shimura <kouya@xxxxxxxxxxxxxx>. Thanks!
>     Signed-off-by: Keir Fraser <keir@xxxxxxxxxxxxx>

... I view this as a pretty odd justification for the change, when imo the
bogus loops should instead have been adjusted.

Jan

> diff --git a/xen/common/domctl.c b/xen/common/domctl.c
> index 09a1e84d98e0..5d29667b7c3d 100644
> --- a/xen/common/domctl.c
> +++ b/xen/common/domctl.c
> @@ -463,19 +463,13 @@ long do_domctl(XEN_GUEST_HANDLE(xen_domctl_t) u_domctl)
>      case XEN_DOMCTL_getdomaininfo:
>      {
>          struct domain *d;
> -        domid_t dom;
> -
> -        dom = op->domain;
> -        if ( dom == DOMID_SELF )
> -            dom = current->domain->domain_id;
> +        domid_t dom = op->domain;
> 
>          rcu_read_lock(&domlist_read_lock);
> 
>          for_each_domain ( d )
> -        {
>              if ( d->domain_id >= dom )
>                  break;
> -        }
> 
>          if ( d == NULL )
>          {