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 enabled.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Fixes: c02027b5742b ("x86/kvm: Disable kvmclock on all CPUs on shutdown")
Reviewed-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Wanpeng Li <wanpengli@tencent.com>
---
 arch/x86/kernel/kvmclock.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index fb8f52149be9..f2fff625576d 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -24,8 +24,8 @@
 
 static int kvmclock __initdata = 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;
+static int msr_kvm_system_time __ro_after_init;
+static int msr_kvm_wall_clock __ro_after_init;
 static u64 kvm_sched_clock_offset __ro_after_init;
 
 static int __init parse_no_kvmclock(char *arg)
@@ -195,7 +195,8 @@ static void kvm_setup_secondary_clock(void)
 
 void kvmclock_disable(void)
 {
-	native_write_msr(msr_kvm_system_time, 0, 0);
+	if (msr_kvm_system_time)
+		native_write_msr(msr_kvm_system_time, 0, 0);
 }
 
 static void __init kvmclock_init_mem(void)
@@ -294,7 +295,10 @@ void __init kvmclock_init(void)
 	if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2)) {
 		msr_kvm_system_time = MSR_KVM_SYSTEM_TIME_NEW;
 		msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK_NEW;
-	} else if (!kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
+	} else if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
+		msr_kvm_system_time = MSR_KVM_SYSTEM_TIME;
+		msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK;
+	} else {
 		return;
 	}
 
-- 
2.41.0

On Tue, Dec 05, 2023 at 03:45:01AM +0300, Kirill A. Shutemov wrote:
> 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 enabled.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Fixes: c02027b5742b ("x86/kvm: Disable kvmclock on all CPUs on shutdown")
> Reviewed-by: Sean Christopherson <seanjc@google.com>
> Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Wanpeng Li <wanpengli@tencent.com>

Paolo, Sean, any chance you can get it in through KVM tree while the rest
of kexec patchset is pending? The problem is visible on normal reboot too.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

On Tue, Dec 12, 2023, Kirill A. Shutemov wrote:
> On Tue, Dec 05, 2023 at 03:45:01AM +0300, Kirill A. Shutemov wrote:
> > 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 enabled.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > Fixes: c02027b5742b ("x86/kvm: Disable kvmclock on all CPUs on shutdown")
> > Reviewed-by: Sean Christopherson <seanjc@google.com>
> > Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> > Cc: Paolo Bonzini <pbonzini@redhat.com>
> > Cc: Wanpeng Li <wanpengli@tencent.com>
> 
> Paolo, Sean, any chance you can get it in through KVM tree while the rest
> of kexec patchset is pending? The problem is visible on normal reboot too.

Paolo is going to grab this (possibly for 6.7-rc?).  I'll keep this tagged on my
end in case that doesn't happen "soon".

On Wed, Dec 13, 2023 at 09:22:34AM -0800, Sean Christopherson wrote:
> On Tue, Dec 12, 2023, Kirill A. Shutemov wrote:
> > On Tue, Dec 05, 2023 at 03:45:01AM +0300, Kirill A. Shutemov wrote:
> > > 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 enabled.
> > > 
> > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > > Fixes: c02027b5742b ("x86/kvm: Disable kvmclock on all CPUs on shutdown")
> > > Reviewed-by: Sean Christopherson <seanjc@google.com>
> > > Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> > > Cc: Paolo Bonzini <pbonzini@redhat.com>
> > > Cc: Wanpeng Li <wanpengli@tencent.com>
> > 
> > Paolo, Sean, any chance you can get it in through KVM tree while the rest
> > of kexec patchset is pending? The problem is visible on normal reboot too.
> 
> Paolo is going to grab this (possibly for 6.7-rc?).  I'll keep this tagged on my
> end in case that doesn't happen "soon".

Sean, any update on this?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

On Thu, Jan 04, 2024, Kirill A. Shutemov wrote:
> On Wed, Dec 13, 2023 at 09:22:34AM -0800, Sean Christopherson wrote:
> > On Tue, Dec 12, 2023, Kirill A. Shutemov wrote:
> > > On Tue, Dec 05, 2023 at 03:45:01AM +0300, Kirill A. Shutemov wrote:
> > > > 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 enabled.
> > > > 
> > > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > > > Fixes: c02027b5742b ("x86/kvm: Disable kvmclock on all CPUs on shutdown")
> > > > Reviewed-by: Sean Christopherson <seanjc@google.com>
> > > > Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> > > > Cc: Paolo Bonzini <pbonzini@redhat.com>
> > > > Cc: Wanpeng Li <wanpengli@tencent.com>
> > > 
> > > Paolo, Sean, any chance you can get it in through KVM tree while the rest
> > > of kexec patchset is pending? The problem is visible on normal reboot too.
> > 
> > Paolo is going to grab this (possibly for 6.7-rc?).  I'll keep this tagged on my
> > end in case that doesn't happen "soon".
> 
> Sean, any update on this?

'Tis now in kvm/next, commit 1c6d984f523f ("x86/kvm: Do not try to disable kvmclock
if it was not enabled").  The one time procrastinating on responding actually worked. ;-)