Re: [PATCH 0/6] KVM: nSVM: Fix issues when SMM is entered from L2

From: Paolo Bonzini
Date: Thu Jul 08 2021 - 13:40:24 EST

On 28/06/21 12:44, Vitaly Kuznetsov wrote:
This is a continuation of "[PATCH RFC] KVM: nSVM: Fix L1 state corruption
upon return from SMM".

VMCB split commit 4995a3685f1b ("KVM: SVM: Use a separate vmcb for the
nested L2 guest") broke return from SMM when we entered there from guest
(L2) mode. Gen2 WS2016/Hyper-V is known to do this on boot. The problem
appears to be that VMCB01 gets irreversibly destroyed during SMM execution.
Previously, we used to have 'hsave' VMCB where regular (pre-SMM) L1's state
was saved upon nested_svm_vmexit() but now we just switch to VMCB01 from

While writing a selftest for the issue, I've noticed that 'svm->nested.ctl'
doesn't get restored after KVM_GET_NESTED_STATE/KVM_SET_NESTED_STATE cycle
when guest happens to be in SMM triggered from L2. "KVM: nSVM: Restore
nested control upon leaving SMM" is aimed to fix that.

First two patches of the series add missing sanity checks for
MSR_VM_HSAVE_PA which has to be page aligned and not zero.

Vitaly Kuznetsov (6):
KVM: nSVM: Check the value written to MSR_VM_HSAVE_PA
KVM: nSVM: Check that VM_HSAVE_PA MSR was set before VMRUN
KVM: nSVM: Introduce svm_copy_nonvmloadsave_state()
KVM: nSVM: Fix L1 state corruption upon return from SMM
KVM: nSVM: Restore nested control upon leaving SMM
KVM: selftests: smm_test: Test SMM enter from L2

arch/x86/kvm/svm/nested.c | 45 +++++++-----
arch/x86/kvm/svm/svm.c | 51 +++++++++++++-
arch/x86/kvm/svm/svm.h | 4 ++
tools/testing/selftests/kvm/x86_64/smm_test.c | 70 +++++++++++++++++--
4 files changed, 144 insertions(+), 26 deletions(-)

Queued, thanks.