KVM: nVMX: Defer the MMU reload to the normal path on an EPTP switch

Defer reloading the MMU after a EPTP successful EPTP switch.  The VMFUNC
instruction itself is executed in the previous EPTP context, any side
effects, e.g. updating RIP, should occur in the old context.  Practically
speaking, this bug is benign as VMX doesn't touch the MMU when skipping
an emulated instruction, nor does queuing a single-step #DB.  No other
post-switch side effects exist.

Fixes: 41ab93727467 ("KVM: nVMX: Emulate EPTP switching for the L1 hypervisor")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210305011101.3597423-14-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index bd1343a0896ec4b509d60e9c4989bf303792d74e..d74abd7784295fe202e5c2f124e8d9bed26d20a6 100644 (file)
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -5481,16 +5481,11 @@ static int nested_vmx_eptp_switching(struct kvm_vcpu *vcpu,
                if (!nested_vmx_check_eptp(vcpu, new_eptp))
                        return 1;
 
-               kvm_mmu_unload(vcpu);
                mmu->ept_ad = accessed_dirty;
                mmu->mmu_role.base.ad_disabled = !accessed_dirty;
                vmcs12->ept_pointer = new_eptp;
-               /*
-                * TODO: Check what's the correct approach in case
-                * mmu reload fails. Currently, we just let the next
-                * reload potentially fail
-                */
-               kvm_mmu_reload(vcpu);
+
+               kvm_make_request(KVM_REQ_MMU_RELOAD, vcpu);
        }
 
        return 0;