If we're using nested EPT, why not do away with this allocation
altogether, and just use the vpid from vmcs12? The TLB is tagged by
{PCID, EP4TA, VPID}, and the shadow EP4TA will be different from any
L1 EP4TA.
On Thu, Jul 19, 2018 at 11:59 AM, Roman Kagan <rkagan@xxxxxxxxxxxxx> wrote:
> VPID for the nested vcpu is allocated at vmx_create_vcpu whenever nested
> vmx is turned on with the module parameter.
>
> However, it's only freed if the L1 guest has executed VMXON which is not
> a given.
>
> As a result, on a system with nested==on every creation+deletion of an
> L1 vcpu without running an L2 guest results in leaking one vpid. Since
> the total number of vpids is limited to 64k, they can eventually get
> exhausted, preventing L2 from starting.
>
> Delay allocation of the L2 vpid until VMXON emulation, thus matching its
> freeing.
>
> Fixes: 5c614b3583e7b6dab0c86356fa36c2bcbb8322a0
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Roman Kagan <rkagan@xxxxxxxxxxxxx>
> ---
> arch/x86/kvm/vmx.c | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index e30da9a2430c..fcb33ba15bb9 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -7893,6 +7893,8 @@ static int enter_vmx_operation(struct kvm_vcpu *vcpu)
> HRTIMER_MODE_REL_PINNED);
> vmx->nested.preemption_timer.function = vmx_preemption_timer_fn;
>
> + vmx->nested.vpid02 = allocate_vpid();
> +
> vmx->nested.vmxon = true;
> return 0;
>
> @@ -10370,11 +10372,9 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
> goto free_vmcs;
> }
>
> - if (nested) {
> + if (nested)
> nested_vmx_setup_ctls_msrs(&vmx->nested.msrs,
> kvm_vcpu_apicv_active(&vmx->vcpu));
> - vmx->nested.vpid02 = allocate_vpid();
> - }
>
> vmx->nested.posted_intr_nv = -1;
> vmx->nested.current_vmptr = -1ull;
> @@ -10391,7 +10391,6 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
> return &vmx->vcpu;
>
> free_vmcs:
> - free_vpid(vmx->nested.vpid02);
> free_loaded_vmcs(vmx->loaded_vmcs);
> free_msrs:
> kfree(vmx->guest_msrs);
> --
> 2.17.1
>
