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doc: add VPID allocation to nested virtualization tutorial

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Tracked-On: #6289
Signed-off-by: Zide Chen <zide.chen@intel.com>
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Zide Chen 2021-09-13 11:31:02 -07:00 committed by wenlingz
parent e9eb72d319
commit e4c69546a0
1 changed files with 14 additions and 0 deletions
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doc/tutorials/nvmx_virtualization.rst
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@ -91,6 +91,20 @@ Constraints on L1 guest configuration:
* Only the ``SCHED_NOOP`` scheduler is supported. ACRN can't receive timer interrupts * Only the ``SCHED_NOOP`` scheduler is supported. ACRN can't receive timer interrupts
on LAPIC passthrough pCPUs on LAPIC passthrough pCPUs
VPID allocation
===============
ACRN doesn't emulate L2 VPIDs and allocates VPIDs for L1 VMs from the reserved top
16-bit VPID range (``0x10000U - CONFIG_MAX_VM_NUM * MAX_VCPUS_PER_VM`` and up).
If the L1 hypervisor enables VPID for L2 VMs and allocates L2 VPIDs not in this
range, ACRN doesn't need to flush L2 VPID during L2 VMX transitions.
This is the expected behavior in most of the time. But in special cases where a
L2 VPID allocated by L1 hypervisor is within this reserved range, it's possible
that this L2 VPID may conflict with a L1 VPID. In this case, ACRN flushes VPID
on L2 VMExit/VMEntry that are associated with this L2 VPID, which may significantly
negatively impact performances of this L2 VM.
Service OS VM configuration Service OS VM configuration
*************************** ***************************