Re: PCI passthrough for HVM with stubdomain broken by "tools/libxl: handle the iomem parameter with the memory_mapping hcall"

["Jan Beulich" <JBeulich@suse.com>]

>>> On 23.06.16 at 11:23, <marmarek@invisiblethingslab.com> wrote:
> On Thu, Jun 23, 2016 at 11:18:24AM +0200, Marek Marczykowski-Górecki wrote:
>> On Thu, Jun 23, 2016 at 03:12:47AM -0600, Jan Beulich wrote:
>> > >>> On 23.06.16 at 10:57, <marmarek@invisiblethingslab.com> wrote:
>> > > On Thu, Jun 23, 2016 at 02:32:29AM -0600, Jan Beulich wrote:
>> > >> I wonder what good the duplication of the returned domain ID does: I'm
>> > >> tempted to remove the one in the command-specific structure. Does
>> > >> anyone have insight into why it was done that way?
>> > > 
>> > > Isn't XEN_DOMCTL_getdomaininfo supposed to return info about first
>> > > existing domain with ID >= passed one? Reading various comments in code
>> > > it looks to be used to domain enumeration. This patch changes this
>> > > behaviour.
>> > 
>> > No, it doesn't. It adjusts the behavior only for the DM case (which
>> > isn't supposed to get information on other than the target domain,
>> > i.e. in this one specific case the very domain ID needs to be passed
>> > in).
>> 
>> int xc_domain_getinfo(xc_interface *xch,
>>                       uint32_t first_domid,
>>                       unsigned int max_doms,
>>                       xc_dominfo_t *info)
>> {
>>     unsigned int nr_doms;
>>     uint32_t next_domid = first_domid;
>>     DECLARE_DOMCTL;
>>     int rc = 0;
>> 
>>     memset(info, 0, max_doms*sizeof(xc_dominfo_t));
>> 
>>     for ( nr_doms = 0; nr_doms < max_doms; nr_doms++ )
>>     {   
>>         domctl.cmd = XEN_DOMCTL_getdomaininfo;
>>         domctl.domain = (domid_t)next_domid;
>>         if ( (rc = do_domctl(xch, &domctl)) < 0 )
>>             break;
>>         info->domid      = (uint16_t)domctl.domain;
>> (...)
>>         next_domid = (uint16_t)domctl.domain + 1;
>> 
>> 
>> Looks like heavily dependent on XEN_DOMCTL_getdomaininfo returning next 
> valid
>> domain.
> 
> Hmm, looks like I've misread you patch. Reading again...
> 
> But now I see rcu_read_lock(&domlist_read_lock) is gets called only when
> looping over domains, but rcu_read_unlock is called in any case. Is it
> correct?

How that? There is this third hunk:

@@ -885,6 +892,9 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xe
         copyback = 1;
 
     getdomaininfo_out:
+        if ( dom == DOMID_INVALID )
+            break;
+
         rcu_read_unlock(&domlist_read_lock);
         d = NULL;
         break;

Jan

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