KVM: nVMX: Sync all PGDs on nested transition with shadow paging

Trigger a full TLB flush on behalf of the guest on nested VM-Enter and
VM-Exit when VPID is disabled for L2.  kvm_mmu_new_pgd() syncs only the
current PGD, which can theoretically leave stale, unsync'd entries in a
previous guest PGD, which could be consumed if L2 is allowed to load CR3
with PCID_NOFLUSH=1.

Rename KVM_REQ_HV_TLB_FLUSH to KVM_REQ_TLB_FLUSH_GUEST so that it can
be utilized for its obvious purpose of emulating a guest TLB flush.

Note, there is no change the actual TLB flush executed by KVM, even
though the fast PGD switch uses KVM_REQ_TLB_FLUSH_CURRENT.  When VPID is
disabled for L2, vpid02 is guaranteed to be '0', and thus
nested_get_vpid02() will return the VPID that is shared by L1 and L2.

Generate the request outside of kvm_mmu_new_pgd(), as getting the common
helper to correctly identify which requested is needed is quite painful.
E.g. using KVM_REQ_TLB_FLUSH_GUEST when nested EPT is in play is wrong as
a TLB flush from the L1 kernel's perspective does not invalidate EPT
mappings.  And, by using KVM_REQ_TLB_FLUSH_GUEST, nVMX can do future
simplification by moving the logic into nested_vmx_transition_tlb_flush().

Fixes: 41fab65e7c44 ("KVM: nVMX: Skip MMU sync on nested VMX transition when possible")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210609234235.1244004-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 12 insertions, 5 deletions

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index ee89b48730b6..a9906c8344b8 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -1131,12 +1131,19 @@ static int nested_vmx_load_cr3(struct kvm_vcpu *vcpu, unsigned long cr3,
 
 	/*
 	 * Unconditionally skip the TLB flush on fast CR3 switch, all TLB
-	 * flushes are handled by nested_vmx_transition_tlb_flush().  See
-	 * nested_vmx_transition_mmu_sync for details on skipping the MMU sync.
+	 * flushes are handled by nested_vmx_transition_tlb_flush().
 	 */
-	if (!nested_ept)
-		kvm_mmu_new_pgd(vcpu, cr3, true,
-				!nested_vmx_transition_mmu_sync(vcpu));
+	if (!nested_ept) {
+		kvm_mmu_new_pgd(vcpu, cr3, true, true);
+
+		/*
+		 * A TLB flush on VM-Enter/VM-Exit flushes all linear mappings
+		 * across all PCIDs, i.e. all PGDs need to be synchronized.
+		 * See nested_vmx_transition_mmu_sync() for more details.
+		 */
+		if (nested_vmx_transition_mmu_sync(vcpu))
+			kvm_make_request(KVM_REQ_TLB_FLUSH_GUEST, vcpu);
+	}
 
 	vcpu->arch.cr3 = cr3;
 	kvm_register_mark_available(vcpu, VCPU_EXREG_CR3);