On Thu, Nov 25, 2021 at 9:49 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> Fully emulate a guest TLB flush on nested VM-Enter which changes vpid12,
> i.e. L2's VPID, instead of simply doing INVVPID to flush real hardware's
> TLB entries for vpid02. From L1's perspective, changing L2's VPID is
> effectively a TLB flush unless "hardware" has previously cached entries
> for the new vpid12. Because KVM tracks only a single vpid12, KVM doesn't
> know if the new vpid12 has been used in the past and so must treat it as
> a brand new, never been used VPID, i.e. must assume that the new vpid12
> represents a TLB flush from L1's perspective.
>
> For example, if L1 and L2 share a CR3, the first VM-Enter to L2 (with a
> VPID) is effectively a TLB flush as hardware/KVM has never seen vpid12
> and thus can't have cached entries in the TLB for vpid12.
>
> Reported-by: Lai Jiangshan <jiangshanlai+lkml@xxxxxxxxx>
> Fixes: 5c614b3583e7 ("KVM: nVMX: nested VPID emulation")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
> arch/x86/kvm/vmx/nested.c | 37 +++++++++++++++++--------------------
> 1 file changed, 17 insertions(+), 20 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 2ef1d5562a54..dafe5881ae51 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -1162,29 +1162,26 @@ static void nested_vmx_transition_tlb_flush(struct kvm_vcpu *vcpu,
> WARN_ON(!enable_vpid);
>
> /*
> - * If VPID is enabled and used by vmc12, but L2 does not have a unique
> - * TLB tag (ASID), i.e. EPT is disabled and KVM was unable to allocate
> - * a VPID for L2, flush the current context as the effective ASID is
> - * common to both L1 and L2.
> - *
> - * Defer the flush so that it runs after vmcs02.EPTP has been set by
> - * KVM_REQ_LOAD_MMU_PGD (if nested EPT is enabled) and to avoid
> - * redundant flushes further down the nested pipeline.
> - *
> - * If a TLB flush isn't required due to any of the above, and vpid12 is
> - * changing then the new "virtual" VPID (vpid12) will reuse the same
> - * "real" VPID (vpid02), and so needs to be flushed. There's no direct
> - * mapping between vpid02 and vpid12, vpid02 is per-vCPU and reused for
> - * all nested vCPUs. Remember, a flush on VM-Enter does not invalidate
> - * guest-physical mappings, so there is no need to sync the nEPT MMU.
> + * VPID is enabled and in use by vmcs12. If vpid12 is changing, then
> + * emulate a guest TLB flush as KVM does not track vpid12 history nor
> + * is the VPID incorporated into the MMU context. I.e. KVM must assume
> + * that the new vpid12 has never been used and thus represents a new
> + * guest ASID that cannot have entries in the TLB.
> */
> - if (!nested_has_guest_tlb_tag(vcpu)) {
> - kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu);
> - } else if (is_vmenter &&
> - vmcs12->virtual_processor_id != vmx->nested.last_vpid) {
> + if (is_vmenter && vmcs12->virtual_processor_id != vmx->nested.last_vpid) {
> vmx->nested.last_vpid = vmcs12->virtual_processor_id;
How about when vmx->nested.last_vpid == vmcs12->virtual_processor_id == 0?
I think KVM_REQ_TLB_FLUSH_GUEST is needed in this case too.
> - vpid_sync_context(nested_get_vpid02(vcpu));
> + kvm_make_request(KVM_REQ_TLB_FLUSH_GUEST, vcpu);
> + return;
> }
> +
> + /*
> + * If VPID is enabled, used by vmc12, and vpid12 is not changing but
> + * does not have a unique TLB tag (ASID), i.e. EPT is disabled and
> + * KVM was unable to allocate a VPID for L2, flush the current context
> + * as the effective ASID is common to both L1 and L2.
> + */
> + if (!nested_has_guest_tlb_tag(vcpu))
> + kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu);
> }
>
> static bool is_bitwise_subset(u64 superset, u64 subset, u64 mask)
> --
> 2.34.0.rc2.393.gf8c9666880-goog
>
