Re: [PATCH v3 2/2] libxc: Defer initialization of start_page for HVM guests

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 01/07/2016 06:43 AM, Roger Pau Monné wrote:
> El 06/01/16 a les 21.03, Boris Ostrovsky ha escrit:
>>   
>>   static int bootlate_hvm(struct xc_dom_image *dom)
>>   {
>> -    DOMPRINTF("%s: doing nothing", __func__);
>> +    uint32_t domid = dom->guest_domid;
>> +    xc_interface *xch = dom->xch;
>> +
>> +    if ( !dom->device_model )
>> +    {
>> +        struct hvm_start_info *start_info;
>> +        size_t start_info_size = sizeof(*start_info);
>> +        void *start_page;
>> +        struct hvm_modlist_entry *modlist;
>> +        size_t cmdline_size = 0;
>> +
>> +        if ( dom->cmdline )
>> +        {
>> +            cmdline_size = ROUNDUP(strlen(dom->cmdline) + 1, 8);
>> +            start_info_size += cmdline_size;
>> +        }
>> +        if ( dom->ramdisk_blob )
>> +            start_info_size += sizeof(*modlist); /* Limited to one module. */
> The size calculations are duplicated, could you either stash
> start_info_size into xc_dom_image, or simply do the memory allocation
> (xc_dom_alloc_segment) inside of bootlate_hvm? (I think the latter would
> be better if possible).

I didn't want to do the first because we'd use that information (two 
pieces --- we need to to know both the size of the extra chunk and where 
modlist starts) only once and it's not on a critical path. You can, of 
course, argue that we increase text size.

The problem with the second approach is that while it does seem to work 
I don't know whether we can delay allocations until bootlate(): notice 
how we print dom->virt_alloc_end in xc_dom_build_image() which to me 
indicates some "finality" as far as allocations for domain are concerned.


-boris