KVM: x86: Fix invalid secondary exec controls in vmx_cpuid_update()

The commit [ad756a16: KVM: VMX: Implement PCID/INVPCID for guests with
EPT] introduced the unconditional access to SECONDARY_VM_EXEC_CONTROL,
and this triggers kernel warnings like below on old CPUs:

vmwrite error: reg 401e value a0568000 (err 12)
Pid: 13649, comm: qemu-kvm Not tainted 3.7.0-rc4-test2+ #154
Call Trace:
[<ffffffffa0558d86>] vmwrite_error+0x27/0x29 [kvm_intel]
[<ffffffffa054e8cb>] vmcs_writel+0x1b/0x20 [kvm_intel]
[<ffffffffa054f114>] vmx_cpuid_update+0x74/0x170 [kvm_intel]
[<ffffffffa03629b6>] kvm_vcpu_ioctl_set_cpuid2+0x76/0x90 [kvm]
[<ffffffffa0341c67>] kvm_arch_vcpu_ioctl+0xc37/0xed0 [kvm]
[<ffffffff81143f7c>] ? __vunmap+0x9c/0x110
[<ffffffffa0551489>] ? vmx_vcpu_load+0x39/0x1a0 [kvm_intel]
[<ffffffffa0340ee2>] ? kvm_arch_vcpu_load+0x52/0x1a0 [kvm]
[<ffffffffa032dcd4>] ? vcpu_load+0x74/0xd0 [kvm]
[<ffffffffa032deb0>] kvm_vcpu_ioctl+0x110/0x5e0 [kvm]
[<ffffffffa032e93d>] ? kvm_dev_ioctl+0x4d/0x4a0 [kvm]
[<ffffffff8117dc6f>] do_vfs_ioctl+0x8f/0x530
[<ffffffff81139d76>] ? remove_vma+0x56/0x60
[<ffffffff8113b708>] ? do_munmap+0x328/0x400
[<ffffffff81187c8c>] ? fget_light+0x4c/0x100
[<ffffffff8117e1a1>] sys_ioctl+0x91/0xb0
[<ffffffff815a942d>] system_call_fastpath+0x1a/0x1f

This patch adds a check for the availability of secondary exec
control to avoid these warnings.

Cc: <[e-mail]> [v3.6+]
Signed-off-by: Takashi Iwai <[e-mail]>
Signed-off-by: Marcelo Tosatti <[e-mail]>

arch/x86/kvm/vmx.c

···
 		}
 	}
 
-	exec_control = vmcs_read32(SECONDARY_VM_EXEC_CONTROL);
 	/* Exposing INVPCID only when PCID is exposed */
 	best = kvm_find_cpuid_entry(vcpu, 0x7, 0);
 	if (vmx_invpcid_supported() &&
 	    best && (best->ebx & bit(X86_FEATURE_INVPCID)) &&
 	    guest_cpuid_has_pcid(vcpu)) {
+		exec_control = vmcs_read32(SECONDARY_VM_EXEC_CONTROL);
 		exec_control |= SECONDARY_EXEC_ENABLE_INVPCID;
 		vmcs_write32(SECONDARY_VM_EXEC_CONTROL,
 			     exec_control);
 	} else {
-		exec_control &= ~SECONDARY_EXEC_ENABLE_INVPCID;
-		vmcs_write32(SECONDARY_VM_EXEC_CONTROL,
-			     exec_control);
+		if (cpu_has_secondary_exec_ctrls()) {
+			exec_control = vmcs_read32(SECONDARY_VM_EXEC_CONTROL);
+			exec_control &= ~SECONDARY_EXEC_ENABLE_INVPCID;
+			vmcs_write32(SECONDARY_VM_EXEC_CONTROL,
+				     exec_control);
+		}
 		if (best)
 			best->ebx &= ~bit(X86_FEATURE_INVPCID);
 	}