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Commit 67652ed3 authored by Xiao Guangrong's avatar Xiao Guangrong Committed by Gleb Natapov
Browse files

KVM: MMU: document mmio page fault 



Document it to Documentation/virtual/kvm/mmu.txt

Signed-off-by: default avatarXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 0cbf8e43

Documentation/virtual/kvm/mmu.txt

+9 −2
Original line number Diff line number Diff line
@@ -272,14 +272,21 @@ This is the most complicated event. The cause of a page fault can be: 


Handling a page fault is performed as follows:



 - if the RSV bit of the error code is set, the page fault is caused by guest

   accessing MMIO and cached MMIO information is available.

   - walk shadow page table

   - cache the information to vcpu->arch.mmio_gva, vcpu->arch.access and

     vcpu->arch.mmio_gfn, and call the emulator

 - if needed, walk the guest page tables to determine the guest translation

   (gva->gpa or ngpa->gpa)

   - if permissions are insufficient, reflect the fault back to the guest

 - determine the host page

   - if this is an mmio request, there is no host page; call the emulator

     to emulate the instruction instead

   - if this is an mmio request, there is no host page; cache the info to

     vcpu->arch.mmio_gva, vcpu->arch.access and vcpu->arch.mmio_gfn

 - walk the shadow page table to find the spte for the translation,

   instantiating missing intermediate page tables as necessary

   - If this is an mmio request, cache the mmio info to the spte and set some

     reserved bit on the spte (see callers of kvm_mmu_set_mmio_spte_mask)

 - try to unsynchronize the page

   - if successful, we can let the guest continue and modify the gpte

 - emulate the instruction