Merge branch 'kvm-updates-2.6.26' of git://git.kernel.org/pub/scm/linux/kernel/git/avi/kvm

* 'kvm-updates-2.6.26' of git://git.kernel.org/pub/scm/linux/kernel/git/avi/kvm: (147 commits)
  KVM: kill file->f_count abuse in kvm
  KVM: MMU: kvm_pv_mmu_op should not take mmap_sem
  KVM: SVM: remove selective CR0 comment
  KVM: SVM: remove now obsolete FIXME comment
  KVM: SVM: disable CR8 intercept when tpr is not masking interrupts
  KVM: SVM: sync V_TPR with LAPIC.TPR if CR8 write intercept is disabled
  KVM: export kvm_lapic_set_tpr() to modules
  KVM: SVM: sync TPR value to V_TPR field in the VMCB
  KVM: ppc: PowerPC 440 KVM implementation
  KVM: Add MAINTAINERS entry for PowerPC KVM
  KVM: ppc: Add DCR access information to struct kvm_run
  ppc: Export tlb_44x_hwater for KVM
  KVM: Rename debugfs_dir to kvm_debugfs_dir
  KVM: x86 emulator: fix lea to really get the effective address
  KVM: x86 emulator: fix smsw and lmsw with a memory operand
  KVM: x86 emulator: initialize src.val and dst.val for register operands
  KVM: SVM: force a new asid when initializing the vmcb
  KVM: fix kvm_vcpu_kick vs __vcpu_run race
  KVM: add ioctls to save/store mpstate
  KVM: Rename VCPU_MP_STATE_* to KVM_MP_STATE_*
  ...

1 files changed, 41 insertions, 0 deletions

diff --git a/Documentation/powerpc/kvm_440.txt b/Documentation/powerpc/kvm_440.txt
new file mode 100644
index 000000000000..c02a003fa03a
--- /dev/null
+++ b/Documentation/powerpc/kvm_440.txt
@@ -0,0 +1,41 @@
+Hollis Blanchard <hollisb@us.ibm.com>
+15 Apr 2008
+
+Various notes on the implementation of KVM for PowerPC 440:
+
+To enforce isolation, host userspace, guest kernel, and guest userspace all
+run at user privilege level. Only the host kernel runs in supervisor mode.
+Executing privileged instructions in the guest traps into KVM (in the host
+kernel), where we decode and emulate them. Through this technique, unmodified
+440 Linux kernels can be run (slowly) as guests. Future performance work will
+focus on reducing the overhead and frequency of these traps.
+
+The usual code flow is started from userspace invoking an "run" ioctl, which
+causes KVM to switch into guest context. We use IVPR to hijack the host
+interrupt vectors while running the guest, which allows us to direct all
+interrupts to kvmppc_handle_interrupt(). At this point, we could either
+- handle the interrupt completely (e.g. emulate "mtspr SPRG0"), or
+- let the host interrupt handler run (e.g. when the decrementer fires), or
+- return to host userspace (e.g. when the guest performs device MMIO)
+
+Address spaces: We take advantage of the fact that Linux doesn't use the AS=1
+address space (in host or guest), which gives us virtual address space to use
+for guest mappings. While the guest is running, the host kernel remains mapped
+in AS=0, but the guest can only use AS=1 mappings.
+
+TLB entries: The TLB entries covering the host linear mapping remain
+present while running the guest. This reduces the overhead of lightweight
+exits, which are handled by KVM running in the host kernel. We keep three
+copies of the TLB:
+ - guest TLB: contents of the TLB as the guest sees it
+ - shadow TLB: the TLB that is actually in hardware while guest is running
+ - host TLB: to restore TLB state when context switching guest -> host
+When a TLB miss occurs because a mapping was not present in the shadow TLB,
+but was present in the guest TLB, KVM handles the fault without invoking the
+guest. Large guest pages are backed by multiple 4KB shadow pages through this
+mechanism.
+
+IO: MMIO and DCR accesses are emulated by userspace. We use virtio for network
+and block IO, so those drivers must be enabled in the guest. It's possible
+that some qemu device emulation (e.g. e1000 or rtl8139) may also work with
+little effort.