Re: [Xen-devel] [PATCH RFC v2 2/4] x86/mem_access: mem_access and mem_event changes to support PV domains

["Aravindh Puthiyaparambil (aravindp)" <aravindp@xxxxxxxxx>]

>> +static int mem_access_set_default(struct domain *d, uint64_t
>*start_page,
>> +                           xenmem_access_t access) {
>> +    struct p2m_domain *p2m = p2m_get_hostp2m(d);
>> +    struct page_info *page;
>> +    struct page_list_head head;
>> +    p2m_access_t a;
>> +    int rc = 0, ctr = 0;
>> +
>> +    if ( !is_pv_domain(d) )
>> +        return -ENOSYS;
>> +
>> +    ASSERT(shadow_mode_enabled(d));
>> +
>> +    rc = p2m_convert_xenmem_access(p2m, access, &a);
>> +    if ( rc != 0 )
>> +        return rc;
>> +
>> +    /*
>> +     * For PV domains we only support r, rw, rx, rx2rw and rwx access
>> +     * permissions
>> +     */
>> +    switch ( a )
>> +    {
>> +    case p2m_access_n:
>> +    case p2m_access_w:
>> +    case p2m_access_x:
>> +    case p2m_access_wx:
>> +    case p2m_access_n2rwx:
>> +        return -EINVAL;
>> +    default:
>> +        break;
>> +    }
>> +
>> +    paging_lock_recursive(d);
>> +
>> +    if ( *start_page )
>> +    {
>> +        head.next = (struct page_info *)*start_page;
>
>What guarantees that the continuation page is still on d->page_list, or that
>now other page got inserted ahead of it? And anyway you're iterating the list
>without holding d->page_alloc_lock.

Good point. Should I grab the lock and release it only when the hypercall 
completes?

Thanks,
Aravindh


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