[suspend/resume] Initiating grant table

[Jean-Yves Migeon <jean-yves.migeon%espci.fr@localhost>]

Hi list,

Some questions regarding the manipulation and initiation of grant tables 
(arch/xen/xen/xengnt.c), when called during hypervisor attach upon 
autoconf part.

Most of it deals with the setup of the grant table and grant table 
entries, but I would like to see if I am not mistaken.

My biggest problem (as of now :o ) being the way Xen and NetBSD both 
cooperate (NetBSD being a PV guest, without using HVM instructions) for 
memory management, especially for shared memory. I did not find any 
"clear" definition on do's and don'ts for a suspend/resume. This may get 
tricky for following cases:

- some parts of a domU kernel which needs, or uses, real physical 
addresses, which will obviously change upon a resume (or migration).

For NetBSD, which parts of the kernel requires such real physical 
addresses, in the situation of a PV guest (with the added level of 
indirection by Xen, m2p and p2m)?

- shared memory mappings, grant tables. If I understand correctly, upon 
setting up the grant table, hypervisor maps the pages in caller's 
address space, which is why NetBSD issues later a call to 
pmap_kenter_ma(), in arch/xen/xen/xengnt.c:154. As the name suggests 
(please correct if I am wrong), NetBSD maps the "grant_table" virtual 
address to the machine one, obtained earlier with the setup hypercall.

However, the man page for pmap(9) does not contain documentation for 
such a fonction. The closest one being pmap_kenter_pa(), for unmanaged 
mapping between virtual and physical addresses. Should I consider the 
pmap_kenter_ma() to work the same way as pmap_kenter_pa(), except that 
it deals with "guest machine" addresses and not real physical ones?

Other than that, one little more question:
- arch/xen/xen/xengnt.c:132, pages variable is malloc()ed to contain the 
list of frame numbers for the grant table. But it is never free()d 
later. Shouldn't be the variable free()d, as we are only intersted by 
the values (frame_list) it points to?


Thanks all, and apologizes for the noise.

Cheers,

--
Jean-Yves Migeon
jean-yves.migeon%espci.fr@localhost