[Xen-devel] out of memory issue on dom0_hvm start

[andrei.semenov@xxxxxxxxx]

Hi all,

I have some troubles to start xen when using dom0 in HVM mode on X86 Intel nuc7i5bnh 
board. After some investigation it seems that  "domheap" memory allocator is out of memory while 
constructing the p2m mapping  (pvh_setup_p2m).  

This misbehavior, from my understanding, is the result of wrong computation of number of pages 
to "give" to dom0 (dom0_compute_nr_pages function). In fact the pages needed to paging 
(dom0_paging_pages function)  are not reserved in this function if  IOMMU mappings are shareable 
with HAP(EPT) mappings. Moreover this memory (for paging needs) is allocated just after that in 
"pvh_setup_p2m" in subroutine "paging_set_allocation". 

Generally speaking from what I understood it's not the IOMMU driver that offers its mappings to HAP,
but it's rather the HAP that shares its mappings with IOMMU driver. So the obvious patch IMHO would 
be:

--- a/xen/arch/x86/dom0_build.c
+++ b/xen/arch/x86/dom0_build.c
@@ -294,8 +294,7 @@ unsigned long __init dom0_compute_nr_pages(
             avail -= max_pdx >> s;
     }
 
-    need_paging = is_hvm_domain(d) &&
-        (!iommu_hap_pt_share || !paging_mode_hap(d));
+    need_paging = is_hvm_domain(d);
     for ( ; ; need_paging = false )
     {
         nr_pages = dom0_nrpages; 

Did anyone encounter the same problem or has some thoughts on this issue?

Andrei.1
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