Messages in this thread | | | Subject | Re: [PATCH v3 0/7] KVM: few more SMM fixes | From | Paolo Bonzini <> | Date | Wed, 22 Sep 2021 16:35:56 +0200 |
| |
On 13/09/21 16:09, Maxim Levitsky wrote: > These are few SMM fixes I was working on last week. > > * Patch 1,2 fixes a minor issue that remained after > commit 37be407b2ce8 ("KVM: nSVM: Fix L1 state corruption upon return from SMM") > > While now, returns to guest mode from SMM work due to restored state from HSAVE > area, the guest entry still sees incorrect HSAVE state. > > This for example breaks return from SMM when the guest is 32 bit, due to PDPTRs > loading which are done using incorrect MMU state which is incorrect, > because it was setup with incorrect L1 HSAVE state. > > V3: updated with review feedback from Sean. > > * Patch 3 fixes a theoretical issue that I introduced with my SREGS2 patchset, > which Sean Christopherson pointed out. > > The issue is that KVM_REQ_GET_NESTED_STATE_PAGES request is not only used > for completing the load of the nested state, but it is also used to complete > exit from SMM to guest mode, and my compatibility hack of pdptrs_from_userspace > was done assuming that this is not done. > > V3: I moved the reset of pdptrs_from_userspace to common x86 code. > > * Patch 4 makes SVM SMM exit to be a bit more similar to how VMX does it > by also raising KVM_REQ_GET_NESTED_STATE_PAGES requests. > > I do have doubts about why we need to do this on VMX though. The initial > justification for this comes from > > 7f7f1ba33cf2 ("KVM: x86: do not load vmcs12 pages while still in SMM") > > With all the MMU changes, I am not sure that we can still have a case > of not up to date MMU when we enter the nested guest from SMM. > On SVM it does seem to work anyway without this. > > * Patch 5 fixes guest emulation failure when unrestricted_guest=0 and we reach > handle_exception_nmi_irqoff. > That function takes stale values from current vmcs and fails not taking into account > the fact that we are emulating invalid guest state now, and thus no VM exit happened. > > * Patch 6 fixed a corner case where return from SMM is slightly corrupting > the L2 segment register state when unrestricted_guest=0 due to real mode segement > caching register logic, but later it restores it correctly from SMMRAM. > Fix this by not failing nested_vmx_enter_non_root_mode and delaying this > failure to the next nested VM entry. > > * Patch 7 fixes another corner case where emulation_required was not updated > correctly on nested VMexit when restoring the L1 segement registers. > > I still track 2 SMM issues: > > 1. When HyperV guest is running nested, and uses SMM enabled OVMF, it crashes and > reboots during the boot process. > > 2. Nested migration on VMX is still broken when L1 floods itself with SMIs. > > Best regards, > Maxim Levitsky > > Maxim Levitsky (7): > KVM: x86: nSVM: refactor svm_leave_smm and smm_enter_smm > KVM: x86: nSVM: restore the L1 host state prior to resuming nested > guest on SMM exit > KVM: x86: reset pdptrs_from_userspace when exiting smm > KVM: x86: SVM: call KVM_REQ_GET_NESTED_STATE_PAGES on exit from SMM > mode > KVM: x86: VMX: synthesize invalid VM exit when emulating invalid guest > state > KVM: x86: nVMX: don't fail nested VM entry on invalid guest state if > !from_vmentry > KVM: x86: nVMX: re-evaluate emulation_required on nested VM exit > > arch/x86/kvm/svm/nested.c | 9 ++- > arch/x86/kvm/svm/svm.c | 131 ++++++++++++++++++++------------------ > arch/x86/kvm/svm/svm.h | 3 +- > arch/x86/kvm/vmx/nested.c | 9 ++- > arch/x86/kvm/vmx/vmx.c | 28 ++++++-- > arch/x86/kvm/vmx/vmx.h | 1 + > arch/x86/kvm/x86.c | 7 ++ > 7 files changed, 113 insertions(+), 75 deletions(-) >
Queued, thanks. However, I'm keeping patch 1 for 5.16 only.
Paolo
| |