Re: [PATCH v2 05/31] x86/virt/tdx: Extend tdx_page_array to support IOMMU_MT

[Xu Yilun]

On Wed, Apr 01, 2026 at 12:17:45AM +0000, Edgecombe, Rick P wrote:
> On Tue, 2026-03-31 at 22:19 +0800, Xu Yilun wrote:
> > > Consider the amount of tricks that are needed to coax the tdx_page_array to
> > > populate the handoff page as needed. It adds 2 pages here, then subtracts
> > > them
> > > later in the callback. Then tweaks the pa in tdx_page_array_populate() to
> > > add
> > > the length...
> > 
> > mm.. The tricky part is the specific memory requirement/allocation, the
> > common part is the pa list contained in a root page. Maybe we only model
> > the later, let the specific user does the memory allocation. Is that
> > closer to your "break concepts apart" idea?
> 
> I haven't wrapped my head around this enough to suggest anything is definitely
> the right approach.
> 
> But yes, the idea would be that the allocation of the list of pages to give to
> the TDX module would be a separate allocation and set of management functions.
> And the the allocation of the pages that are used to communicate the list of
> pages (and in this case other args) with the module would be another set. So
> each type of TDX module arg page format (IOMMU_MT, etc) would be separable, but
> share the page list allocation part only. It looks like Nikolay was probing
> along the same path. Not sure if he had the same solution in mind.
> 
> So for this:
> 1. Allocate a list or array of pages using a generic method.
> 2. Allocate these two IOMMU special pages.
> 3. Allocate memory needed for the seamcall (root pages)
> 
> Hand all three to the wrapper and have it shove them all through in the special
> way it prefers.
> 
> Maybe... Can you write something about the similarities and differences with the
> three types of lists in that series? Like in a compact form?


The common part:
   
         64bit obj type                 root page
   +----------+----------------+    +---------------------+     
   | ...      |  ...           |    | page0 HPA(bit12-51) |--> page0
   +----------+----------------+    +---------------------+     
   |bit 12-51 | root page HPA  |--->| page1 HPA           |--> page1
   +----------+----------------+    +---------------------+
   | ...      |  ...           |    | pageX HPA           |--> pageX
   +----------+----------------+    +---------------------+



The specific objects:

         HPA_LIST_INFO                 root page
   +----------+----------------+    +---------------------+
   |bit 3-11  | first entry    |    | page0 HPA(bit12-51) |
   +----------+----------------+    +---------------------+
   |bit 12-51 | root page HPA  |--->| page1 HPA           |
   +----------+----------------+    +---------------------+
   |bit 55-63 | last entry     |    | pageX HPA           |
   +----------+----------------+    +---------------------+



         HPA_ARRAY_T                   root page                  HPA_ARRAY_T(singleton mode)
   +----------+----------------+    +---------------------+      +----------+----------------+
   |bit 3-11  | Reserved 0     |    | page0 HPA(bit12-51) |      |bit 3-11  | Reserved 0     |
   +----------+----------------+    +---------------------+      +----------+----------------+
   |bit 12-51 | root page HPA  |--->| page1 HPA           |      |bit 12-51 | page0 HPA      |--> page0
   +----------+----------------+    +---------------------+      +----------+----------------+
   |bit 55-63 | last entry     |    | pageX HPA           |      |bit 55-63 | last entry     |
   +----------+----------------+    +---------------------+      +----------+----------------+



         MMIOMT                       root page
   +----------+----------------+    +-----------------------------+-------------------+
   |bit 3-11  | Reserved 0     |    | 2^order page0 HPA(bit12-51) |num pages(bit 0-11)|
   +----------+----------------+    +-----------------------------+-------------------+
   |bit 12-51 | root page HPA  |--->| 2^order page1 HPA           |num pages          |
   +----------+----------------+    +-----------------------------+-------------------+
   |bit 55-63 | Reserved 0     |    | page2 HPA                   |0                  |
   +----------+----------------+    +-----------------------------+-------------------+
                                    | page3 HPA                   |0                  |
                                    +-----------------------------+-------------------+
                                    | pageX HPA                   |0                  |
                                    +-----------------------------+-------------------+



The same thing is they all have root_page_hpa->root_page->page_hpa_list structure.

The differences:

		HPA_LIST_INFO	HPA_ARRAY_T	IOMMU_MT	Note
first entry     Y		N		N		start entry in root page
last entry	Y		Y		N		last entry in root page
num pages	always 0	always 0	Y		for multi-order page
singleton	N		Y		N		try to save a root page


> 
> Also, how much of the earlier code duplication you wanted to avoid was the
> leaking and special error handling stuff?

This is indeed a large part, and now we don't need them anymore.

Others are:
 - the root_page allocation/population/free
 - Too much parameters (struct page **, num_pages, struct page *root...)
   for seamcall wrappers. Or 3 newly defined structures which looks
   pretty much the same and need same implementations like
   tdx_clflush_page().

Thanks,
Yilun