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Subject[PATCH v2 0/8] KVM: x86: nVMX GUEST_CR3 bug fix, and then some...
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*sigh*

v2 was shaping up to be a trivial update, until I started working on
Vitaly's suggestion to add a helper to test for register availability.

The primary purpose of this series is to fix a CR3 corruption in L2
reported by Reto Buerki when running with HLT interception disabled in L1.
On a nested VM-Enter that puts L2 into HLT, KVM never actually enters L2
and instead mimics HLT interception by canceling the nested run and
pretending that VM-Enter to L2 completed and then exited on HLT (which
KVM intercepted). Because KVM never actually runs L2, KVM skips the
pending MMU update for L2 and so leaves a stale value in vmcs02.GUEST_CR3.
If the next wake event for L2 triggers a nested VM-Exit, KVM will refresh
vmcs12->guest_cr3 from vmcs02.GUEST_CR3 and consume the stale value.

Fix the issue by unconditionally writing vmcs02.GUEST_CR3 during nested
VM-Enter instead of deferring the update to vmx_set_cr3(), and skip the
update of GUEST_CR3 in vmx_set_cr3() when running L2. I.e. make the
nested code fully responsible for vmcs02.GUEST_CR3.

Patch 02/08 is a minor optimization to skip the GUEST_CR3 update if
vmcs01 is already up-to-date.

Patches 03 and beyond are Vitaly's fault ;-).

Patches 03 and 04 are tangentially related cleanup to vmx_set_rflags()
that was discovered when working through the avail/dirty testing code.
Ideally they'd be sent as a separate series, but they conflict with the
avail/dirty helper changes and are themselves minor and straightforward.

Patches 05 and 06 clean up the register caching code so that there is a
single enum for all registers which use avail/dirty tracking. While not
a true prerequisite for the avail/dirty helpers, the cleanup allows the
new helpers to take an 'enum kvm_reg' instead of a less helpful 'int reg'.

Patch 07 is the helpers themselves, as suggested by Vitaly.

Patch 08 is a truly optional change to ditch decache_cr3() in favor of
handling CR3 via cache_reg() like any other avail/dirty register.


Note, I collected the Reviewed-by and Tested-by tags for patches 01 and 02
even though I inverted the boolean from 'skip_cr3' to 'update_guest_cr3'.
Please drop the tags if that constitutes a non-trivial functional change.

v2:
- Invert skip_cr3 to update_guest_cr3. [Liran]
- Reword the changelog and comment to be more explicit in detailing
how/when KVM will process a nested VM-Enter without runnin L2. [Liran]
- Added Reviewed-by and Tested-by tags.
- Add a comment in vmx_set_cr3() to explicitly state that nested
VM-Enter is responsible for loading vmcs02.GUEST_CR3. [Jim]
- All of the loveliness in patches 03-08. [Vitaly]

Sean Christopherson (8):
KVM: nVMX: Always write vmcs02.GUEST_CR3 during nested VM-Enter
KVM: VMX: Skip GUEST_CR3 VMREAD+VMWRITE if the VMCS is up-to-date
KVM: VMX: Consolidate to_vmx() usage in RFLAGS accessors
KVM: VMX: Optimize vmx_set_rflags() for unrestricted guest
KVM: x86: Add WARNs to detect out-of-bounds register indices
KVM: x86: Fold 'enum kvm_ex_reg' definitions into 'enum kvm_reg'
KVM: x86: Add helpers to test/mark reg availability and dirtiness
KVM: x86: Fold decache_cr3() into cache_reg()

arch/x86/include/asm/kvm_host.h | 5 +-
arch/x86/kvm/kvm_cache_regs.h | 67 +++++++++++++++++------
arch/x86/kvm/svm.c | 5 --
arch/x86/kvm/vmx/nested.c | 14 ++++-
arch/x86/kvm/vmx/vmx.c | 94 ++++++++++++++++++---------------
arch/x86/kvm/x86.c | 13 ++---
arch/x86/kvm/x86.h | 6 +--
7 files changed, 123 insertions(+), 81 deletions(-)

--
2.22.0

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