KVM: x86/emulator: Emulate RDPID only if it is enabled in guest

When RDTSCP is supported but RDPID is not supported in host,
RDPID emulation is available. However, __kvm_get_msr() would
only fail when RDTSCP/RDPID both are disabled in guest, so
the emulator wouldn't inject a #UD when RDPID is disabled but
RDTSCP is enabled in guest.

Fixes: fb6d4d3 ("KVM: x86: emulate RDPID")
Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
Message-Id: <1dfd46ae5b76d3ed87bde3154d51c64ea64c99c1.1646226788.git.houwenlong.hwl@antgroup.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/emulate.c

@@ -3521,8 +3521,10 @@ static int em_rdpid(struct x86_emulate_ctxt *ctxt)
 {
 	u64 tsc_aux = 0;
 
-	if (ctxt->ops->get_msr(ctxt, MSR_TSC_AUX, &tsc_aux))
+	if (!ctxt->ops->guest_has_rdpid(ctxt))
 		return emulate_ud(ctxt);
+
+	ctxt->ops->get_msr(ctxt, MSR_TSC_AUX, &tsc_aux);
 	ctxt->dst.val = tsc_aux;
 	return X86EMUL_CONTINUE;
 }

arch/x86/kvm/kvm_emulate.h

@@ -226,6 +226,7 @@ struct x86_emulate_ops {
 	bool (*guest_has_long_mode)(struct x86_emulate_ctxt *ctxt);
 	bool (*guest_has_movbe)(struct x86_emulate_ctxt *ctxt);
 	bool (*guest_has_fxsr)(struct x86_emulate_ctxt *ctxt);
+	bool (*guest_has_rdpid)(struct x86_emulate_ctxt *ctxt);
 
 	void (*set_nmi_mask)(struct x86_emulate_ctxt *ctxt, bool masked);
 

arch/x86/kvm/x86.c

@@ -7728,6 +7728,11 @@ static bool emulator_guest_has_fxsr(struct x86_emulate_ctxt *ctxt)
 	return guest_cpuid_has(emul_to_vcpu(ctxt), X86_FEATURE_FXSR);
 }
 
+static bool emulator_guest_has_rdpid(struct x86_emulate_ctxt *ctxt)
+{
+	return guest_cpuid_has(emul_to_vcpu(ctxt), X86_FEATURE_RDPID);
+}
+
 static ulong emulator_read_gpr(struct x86_emulate_ctxt *ctxt, unsigned reg)
 {
 	return kvm_register_read_raw(emul_to_vcpu(ctxt), reg);
@@ -7810,6 +7815,7 @@ static const struct x86_emulate_ops emulate_ops = {
 	.guest_has_long_mode = emulator_guest_has_long_mode,
 	.guest_has_movbe     = emulator_guest_has_movbe,
 	.guest_has_fxsr      = emulator_guest_has_fxsr,
+	.guest_has_rdpid     = emulator_guest_has_rdpid,
 	.set_nmi_mask        = emulator_set_nmi_mask,
 	.get_hflags          = emulator_get_hflags,
 	.exiting_smm         = emulator_exiting_smm,