On Sat, Jun 8, 2024 at 2:10 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> Remove the completely pointess global INVEPT, i.e. EPT TLB flush, from
> KVM's VMX enablement path. KVM always does a targeted TLB flush when
> using a "new" EPT root, in quotes because "new" simply means a root that
> isn't currently being used by the vCPU.
>
> KVM also _deliberately_ runs with stale TLB entries for defunct roots,
> i.e. doesn't do a TLB flush when vCPUs stop using roots, precisely because
> KVM does the flush on first use. As called out by the comment in
> kvm_mmu_load(), the reason KVM flushes on first use is because KVM can't
> guarantee the correctness of past hypervisors.
>
> Jumping back to the global INVEPT, when the painfully terse commit
> 1439442c7b25 ("KVM: VMX: Enable EPT feature for KVM") was added, the
> effective TLB flush being performed was:
>
> static void vmx_flush_tlb(struct kvm_vcpu *vcpu)
> {
> vpid_sync_vcpu_all(to_vmx(vcpu));
> }
>
> I.e. KVM was not flushing EPT TLB entries when allocating a "new" root,
> which very strongly suggests that the global INVEPT during hardware
> enabling was a misguided hack that addressed the most obvious symptom,
> but failed to fix the underlying bug.
Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Paolo
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
> arch/x86/kvm/vmx/vmx.c | 3 ---
> 1 file changed, 3 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 0e3aaf520db2..21dbe20f50ba 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -2832,9 +2832,6 @@ int vmx_hardware_enable(void)
> return r;
> }
>
> - if (enable_ept)
> - ept_sync_global();
> -
> return 0;
> }
>
>
> base-commit: af0903ab52ee6d6f0f63af67fa73d5eb00f79b9a
> --
> 2.45.2.505.gda0bf45e8d-goog
>
