Re: [PATCH] x86/mm: do not mark IO regions as Xen heap

[Jan Beulich <jbeulich@xxxxxxxx>]

On 10.09.2020 19:27, Roger Pau Monné wrote:
> On Thu, Sep 10, 2020 at 04:41:41PM +0200, Jan Beulich wrote:
>> On 10.09.2020 15:35, Roger Pau Monne wrote:
>>> --- a/xen/arch/x86/mm.c
>>> +++ b/xen/arch/x86/mm.c
>>> @@ -271,6 +271,18 @@ static l4_pgentry_t __read_mostly split_l4e;
>>>  #define root_pgt_pv_xen_slots ROOT_PAGETABLE_PV_XEN_SLOTS
>>>  #endif
>>>  
>>> +static void __init assign_io_page(struct page_info *page)
>>> +{
>>> +    set_gpfn_from_mfn(mfn_x(page_to_mfn(page)), INVALID_M2P_ENTRY);
>>> +
>>> +    /* The incremented type count pins as writable. */
>>> +    page->u.inuse.type_info = PGT_writable_page | PGT_validated | 1;
>>> +
>>> +    page_set_owner(page, dom_io);
>>> +
>>> +    page->count_info |= PGC_allocated | 1;
>>> +}
>>
>> ... clarifying its relationship with share_xen_page_with_guest().
> 
> Sure, I think the relation is quite vague now, since this is no longer
> sharing the page (as it's not added to xenpage_list) but rather
> assigning it to dom_io.
> 
> In general I feel this is all quite confusing, and would benefit from
> having some clear rules about what flags and assigned domains non-RAM
> pages have, and how they should be added to the p2m.

Some might call this "organically grown" ... ;-)

Jan