[PATCH v1 5/8] kvm:x86 Enable MSR_IA32_XSS bit 11 and 12 for CET xsaves/xrstors.

[Yang Weijiang]

For kvm Guest OS, right now, only bit 11(user mode CET) and bit 12
(supervisor CET) are supported in XSS MSR, if other bits are being set,
the write to XSS will be skipped.

Signed-off-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
---
 arch/x86/kvm/vmx.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index fa2db6248404..5739ab393b90 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -47,6 +47,7 @@
 #include <asm/virtext.h>
 #include <asm/mce.h>
 #include <asm/fpu/internal.h>
+#include <asm/fpu/types.h>
 #include <asm/perf_event.h>
 #include <asm/debugreg.h>
 #include <asm/kexec.h>
@@ -4323,12 +4324,16 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case MSR_IA32_XSS:
 		if (!vmx_xsaves_supported())
 			return 1;
+
 		/*
-		 * The only supported bit as of Skylake is bit 8, but
-		 * it is not supported on KVM.
+		 * Right now, only support XSS_CET_U[bit 11] and
+		 * XSS_CET_S[bit 12] in MSR_IA32_XSS.
 		 */
-		if (data != 0)
+
+		if (data & ~(XFEATURE_MASK_SHSTK_USER
+			     | XFEATURE_MASK_SHSTK_KERNEL))
 			return 1;
+
 		vcpu->arch.ia32_xss = data;
 		if (vcpu->arch.ia32_xss != host_xss)
 			add_atomic_switch_msr(vmx, MSR_IA32_XSS,
-- 
2.17.1