From c53c632592a427bc01266a8ce7e2f17555a3c247 Mon Sep 17 00:00:00 2001 From: Jim Mattson Date: Tue, 30 Sep 2025 17:14:08 -0700 Subject: [PATCH] KVM: SVM: Disallow EFER.LMSLE when not supported by hardware Modern AMD CPUs do not support segment limit checks in 64-bit mode (i.e. EFER.LMSLE must be zero). Do not allow a guest to set EFER.LMSLE on a CPU that requires the bit to be zero. For backwards compatibility, allow EFER.LMSLE to be set on CPUs that support segment limit checks in 64-bit mode, even though KVM's implementation of the feature is incomplete (e.g. KVM's emulator does not enforce segment limits in 64-bit mode). Fixes: eec4b140c924 ("KVM: SVM: Allow EFER.LMSLE to be set with nested svm") Signed-off-by: Jim Mattson Reviewed-by: Nikunj A Dadhania Reviewed-by: Yosry Ahmed Link: https://lore.kernel.org/r/20251001001529.1119031-3-jmattson@google.com Signed-off-by: Sean Christopherson --- arch/x86/kvm/svm/svm.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index 153c12dbf3eb1..dadb562bd4b9d 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -5320,7 +5320,9 @@ static __init int svm_hardware_setup(void) if (nested) { pr_info("Nested Virtualization enabled\n"); - kvm_enable_efer_bits(EFER_SVME | EFER_LMSLE); + kvm_enable_efer_bits(EFER_SVME); + if (!boot_cpu_has(X86_FEATURE_EFER_LMSLE_MBZ)) + kvm_enable_efer_bits(EFER_LMSLE); r = nested_svm_init_msrpm_merge_offsets(); if (r) -- 2.47.3