I prepared some notes for CR3 involvement in different IO
operations, so here are the notes
- memory-mapped IO & DMA IO:
- Each such operation involves MOV to/from CR3 :
- MOV from CR3 causes "Unconditional VM exit"
- MOV to CR3 causes "Conditional VM exit" :
- The MOV to CR3 instruction causes a VM exit unless the value of its
source operand is equal to one of the CR3-target values specified in
the VMCS (controlled by Hypervisor). This feature allows a guest kernel to
change the CR3 value without causing a world switch to the hypervisor,
provided that the value written into the CR3 register was previously
specified by the hypervisor in the CR3-Target registers. An execution
of MOV to CR3 in VMX non-root operation does not cause a VM exit if
its source operand matches one of these previsously stored values.
If the CR3-target count is n, only the first n (0 .. (n-1)) CR3-target
values do not cause VM-Exit. nth value causes VM-Exit. if n=0 ,
MOV to CR3 always causes VM-Exit.
Please comment if I understood something incorrectly here.
Regards,
K Arun Kumar
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