[PATCH 5.15 075/207] KVM: nVMX: Emulate guest TLB flush on nested VM-Enter with new vpid12

Greg Kroah-Hartman
2021-12-06T15:49:39Z

From: Sean Christopherson <seanjc@google.com>

commit 712494de96f35f3e146b36b752c2afe0fdc0f0cc upstream.

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@gmail.com>
Fixes: 5c614b3583e7 ("KVM: nVMX: nested VPID emulation")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211125014944.536398-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kvm/vmx/nested.c | 37 +++++++++++++++++--------------------
1 file changed, 17 insertions(+), 20 deletions(-)

--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -1180,29 +1180,26 @@ static void nested_vmx_transition_tlb_fl
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;
- 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)