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[Xen-devel] [PATCH v4 0/4] nested vmx: enable VMCS shadowing feature

Changes from v3 to v4:
 - Allocate a buffer in initialization time for data exchange instead of 
runtime allocation (reflect Jun's comment).
 - Move the vmread/vmwrite bitmap logic into nvmx_vcpu_initialise(), also track 
MFN instead of virtual address in the vcpu global data. (reflect Jan's comment).

Changes from v2 to v3:
 - Use pfn_to_paddr() to get the address from frame number instead of doing 
shift directly.
 - Remove some unnecessary initialization code and add "static" to 
vmentry_fields and gpdptr_fields.
 - Enable the VMREAD/VMWRITE bitmap only if nested hvm is enabled.
 - Use clear_page() to set all 0 to the page instead of memset().
 - Use domheap to allocate the VMREAD/VMWRITE bitmap instead of xenheap.

Changes from v1 to v2:
 - Use domain_page_map_to_mfn() instead of virt_to_mfn() to get the machine 
 - Address other comments from Jan, including some programming format, return 
value type, etc.

Latest Intel SDM introduced a new feature "VMCS shadowing" at bit 14 in
Secondary Processor-Based VM-Execution Controls for nested virtualization.

The main purpose of this feature is to reduce or eliminate the number of VM exit
for non-root VMREAD and VMWRITE. It provides the capability to link a
"virtual VMCS" with the current running VMCS, so that after VM entry, the
non-root VMREAD and VMWRITE can get/set related data directly from/to the
"virtual VMCS" without trap and emulation.

A separate bitmap is introduced for VMREAD and VMWRITE, from which hypervisor
can control whether VMREAD/VMWRITE from/to certain VMCS field will trigger
VM exit or directly get/set data by hardware.

With the new feature introduced, all the in "virtual VMCS" need to be operated
by VMREAD and VMWRITE because this VMCS will also be loaded into hardware.
This requires the capability to VMWRITE all the VMCS fields, including those
readonly ones. Intel SDM introduces this functionality at bit 29 in

For details, please refer to:


Dongxiao Xu (4):
  nested vmx: Use a list to store the launched vvmcs for L1 VMM
  nested vmx: use VMREAD/VMWRITE to construct vVMCS if enabled VMCS
  nested vmx: optimize for bulk access of virtual VMCS
  nested vmx: enable VMCS shadowing feature

 xen/arch/x86/hvm/vmx/vmcs.c        |   38 +++++
 xen/arch/x86/hvm/vmx/vvmx.c        |  300 ++++++++++++++++++++++++++++++++----
 xen/include/asm-x86/hvm/vcpu.h     |    2 +
 xen/include/asm-x86/hvm/vmx/vmcs.h |   23 +++-
 xen/include/asm-x86/hvm/vmx/vvmx.h |   22 ++-
 5 files changed, 349 insertions(+), 36 deletions(-)

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