On 2020-12-08 10:12, Jan Beulich wrote: > On 08.12.2020 10:07, Julien Grall wrote: > > On 08/12/2020 05:21, Penny Zheng wrote: > >> --- /dev/null > >> +++ b/docs/designs/1_1_direct-map.md > >> @@ -0,0 +1,87 @@ > >> +# Preface > >> + > >> +The document is an early draft for direct-map memory map > >> +(`guest physical == physical`) of domUs. And right now, it constrains to > >> ARM > > > > s/constrains/limited/ > > > > Aside the interface to the user, you should be able to re-use the same > > code on x86. Note that because the memory layout on x86 is fixed (always > > starting at 0), you would only be able to have only one direct-mapped > > domain. > > Even one seems challenging, if it's truly meant to have all of the > domain's memory direct-mapped: The use of space in the first Mb is > different between host and guest.
Speaking about the case of x86, we can still direct-map the ram regions to the single direct-mapped DomU because neither Xen nor dom0 require those low mem. We don't worry about (i.e. don't direct-map) non-ram regions (or any range that is not reported as usable ram from DomU's PoV (dictated by e820 table), so those can be MMIO or arbitrary mapping with EPT. Fam
