Commit c53c6325 authored by Jim Mattson's avatar Jim Mattson Committed by Sean Christopherson
Browse files

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: eec4b140 ("KVM: SVM: Allow EFER.LMSLE to be set with nested svm")

Signed-off-by: default avatarJim Mattson <jmattson@google.com>
Reviewed-by: default avatarNikunj A Dadhania <nikunj@amd.com>
Reviewed-by: default avatarYosry Ahmed <yosry.ahmed@linux.dev>
Link: https://lore.kernel.org/r/20251001001529.1119031-3-jmattson@google.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent 4793f990

arch/x86/kvm/svm/svm.c

+3 −1
Original line number Diff line number Diff line
@@ -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)