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[Xen-devel] Quick questions- Xen hypervisor

  • To: xen-devel@xxxxxxxxxxxxxxxxxxx
  • From: Ashwini Bhat <apbhat@xxxxxxxx>
  • Date: Wed, 22 Jun 2011 15:38:03 -0700
  • Delivery-date: Wed, 22 Jun 2011 15:39:16 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>

Im trying to understand a little here: 

1) what is cr3 pointing to when in ring 0 i.e. when hypervisor is in control (in a scenario when hypervisor is just booting AND  when hypervisor got control due to a hypercall ) ?

2) The memory layout mentions that 0xffff830000000000 - 0xffff87ffffffffff [5TB, 5*2^40 bytes, PML4:262-271]
is directly mapped. 
but even the calculation of  kernel addresses in __pa does not involve any page table translations. Isnt that as well directly mapped ? 

3) Contrary to the above observation some room is made for xen text in memory management module 
/* Enough page directories to map the Xen text and static data. */
l3_pgentry_t __attribute__ ((__section__ (".bss.page_aligned")))
l2_pgentry_t __attribute__ ((__section__ (".bss.page_aligned")))

Am i right in thinking this is for translations without context switch during hypercalls from VMs ?

Thanks in advance

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