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SubjectRe: [PATCH v3 0/7] KVM: few more SMM fixes
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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

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