Unconditionally forward XSAVES/XRSTORS VM-Exits from L2 to L1, as KVM doesn't utilize the XSS-bitmap (KVM relies on controlling the XSS value in hardware to prevent unauthorized access to XSAVES state). KVM always loads vmcs02 with vmcs12's bitmap, and so any exit _must_ be due to vmcs12's XSS-bitmap. Drop the comment about XSS never being non-zero in anticipation of enabling CET_KERNEL and CET_USER support. Opportunistically WARN if XSAVES is not enabled for L2, as the CPU is supposed to generate #UD before checking the XSS-bitmap. Signed-off-by: Sean Christopherson --- arch/x86/kvm/vmx/nested.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index 2156c9a854f4..846c07380eac 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -6570,14 +6570,17 @@ static bool nested_vmx_l1_wants_exit(struct kvm_vcpu *vcpu, return nested_cpu_has2(vmcs12, SECONDARY_EXEC_WBINVD_EXITING); case EXIT_REASON_XSETBV: return true; - case EXIT_REASON_XSAVES: case EXIT_REASON_XRSTORS: + case EXIT_REASON_XSAVES: + case EXIT_REASON_XRSTORS: /* - * This should never happen, since it is not possible to - * set XSS to a non-zero value---neither in L1 nor in L2. - * If if it were, XSS would have to be checked against - * the XSS exit bitmap in vmcs12. + * Always forward XSAVES/XRSTORS to L1 as KVM doesn't utilize + * XSS-bitmap, and always loads vmcs02 with vmcs12's XSS-bitmap + * verbatim, i.e. any exit is due to L1's bitmap. WARN if + * XSAVES isn't enabled, as the CPU is supposed to inject #UD + * in that case, before consulting the XSS-bitmap. */ - return nested_cpu_has2(vmcs12, SECONDARY_EXEC_ENABLE_XSAVES); + WARN_ON_ONCE(!nested_cpu_has2(vmcs12, SECONDARY_EXEC_ENABLE_XSAVES)); + return true; case EXIT_REASON_UMWAIT: case EXIT_REASON_TPAUSE: return nested_cpu_has2(vmcs12, -- 2.51.0.470.ga7dc726c21-goog