[PATCH 6.1.y] KVM: nSVM: Ignore EFER.LMA if EFER.LME=0 when preparing L2 state

[Sasha Levin <sashal@kernel.org>]

From: Sean Christopherson <seanjc@google.com>

[ Upstream commit 1c4c84a643b704e473cb171f7b61359ff29b12a4 ]

Force EFER.LMA=0 if EFER.LME=0 when preparing L2 state for VMRUN, i.e.
mimic real hardware's behavior of ignoring EFER.LMA if EFER.LME=0.  VMRUN
unfortunately allows the nonsensical combination, i.e. doesn't fail, but
KVM itself has an invariant EFER.LMA can be set et if and only if EFER.LME
is set.   Breaking that invariant can lead to a variety of issue,
particularly in MMU code that keys off EFER.LMA when determining whether to
emulate/virtualization 4/5-level paging versus PAE paging.

Cc: stable@vger.kernel.org
Cc: Yosry Ahmed <yosry@kernel.org>
Link: https://patch.msgid.link/20260902232028.2767071-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
[ sashal: Adjusted context for direct &svm->vcpu and vmcb12->save accesses instead of local vcpu and save aliases. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/x86/kvm/svm/nested.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 86ac990d7a0ef..af9caff998eba 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -559,6 +559,10 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12
 
 	kvm_set_rflags(&svm->vcpu, vmcb12->save.rflags | X86_EFLAGS_FIXED);
 
+	/* SVM ignores EFER.LMA if EFER.LME=0 (instead of failing VMRUN). */
+	if (!(svm->nested.save.efer & EFER_LME))
+		svm->nested.save.efer &= ~EFER_LMA;
+
 	svm_set_efer(&svm->vcpu, svm->nested.save.efer);
 
 	svm_set_cr0(&svm->vcpu, svm->nested.save.cr0);
-- 
2.53.0