[PATCH 04/13] x86/kvm: Do not try to disable kvmclock if it was not enabled

["Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>]

kvm_guest_cpu_offline() tries to disable kvmclock regardless if it is
present in the VM. It leads to write to a MSR that doesn't exist on some
configurations, namely in TDX guest:

	unchecked MSR access error: WRMSR to 0x12 (tried to write 0x0000000000000000)
	at rIP: 0xffffffff8110687c (kvmclock_disable+0x1c/0x30)

kvmclock enabling is gated by CLOCKSOURCE and CLOCKSOURCE2 KVM paravirt
features.

Do not disable kvmclock if it was not enumerated or disabled by user
from kernel command line.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Fixes: c02027b5742b ("x86/kvm: Disable kvmclock on all CPUs on shutdown")
---
 arch/x86/kernel/kvmclock.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index fb8f52149be9..cba2e732e53f 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -22,7 +22,7 @@
 #include <asm/x86_init.h>
 #include <asm/kvmclock.h>
 
-static int kvmclock __initdata = 1;
+static int kvmclock __ro_after_init = 1;
 static int kvmclock_vsyscall __initdata = 1;
 static int msr_kvm_system_time __ro_after_init = MSR_KVM_SYSTEM_TIME;
 static int msr_kvm_wall_clock __ro_after_init = MSR_KVM_WALL_CLOCK;
@@ -195,7 +195,12 @@ static void kvm_setup_secondary_clock(void)
 
 void kvmclock_disable(void)
 {
-	native_write_msr(msr_kvm_system_time, 0, 0);
+	if (!kvm_para_available() || !kvmclock)
+		return;
+
+	if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE) ||
+	    kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2))
+		native_write_msr(msr_kvm_system_time, 0, 0);
 }
 
 static void __init kvmclock_init_mem(void)
-- 
2.41.0