[v3,|,v5.4,2/3] x86/kvm: Disable kvmclock on all CPUs on shutdown

From: Vitaly Kuznetsov <vkuznets@redhat.com>

commit c02027b5742b5aa804ef08a4a9db433295533046 upstream.

Currenly, we disable kvmclock from machine_shutdown() hook and this
only happens for boot CPU. We need to disable it for all CPUs to
guard against memory corruption e.g. on restore from hibernate.

Note, writing '0' to kvmclock MSR doesn't clear memory location, it
just prevents hypervisor from updating the location so for the short
while after write and while CPU is still alive, the clock remains usable
and correct so we don't need to switch to some other clocksource.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210414123544.1060604-4-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
---
 arch/x86/include/asm/kvm_para.h | 4 ++--
 arch/x86/kernel/kvm.c           | 1 +
 arch/x86/kernel/kvmclock.c      | 5 +----
 3 files changed, 4 insertions(+), 6 deletions(-)

On 31/05/21 16:03, Krzysztof Kozlowski wrote:
> From: Vitaly Kuznetsov <vkuznets@redhat.com>
> 
> commit c02027b5742b5aa804ef08a4a9db433295533046 upstream.
> 
> Currenly, we disable kvmclock from machine_shutdown() hook and this
> only happens for boot CPU. We need to disable it for all CPUs to
> guard against memory corruption e.g. on restore from hibernate.
> 
> Note, writing '0' to kvmclock MSR doesn't clear memory location, it
> just prevents hypervisor from updating the location so for the short
> while after write and while CPU is still alive, the clock remains usable
> and correct so we don't need to switch to some other clocksource.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> Message-Id: <20210414123544.1060604-4-vkuznets@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
> ---
>   arch/x86/include/asm/kvm_para.h | 4 ++--
>   arch/x86/kernel/kvm.c           | 1 +
>   arch/x86/kernel/kvmclock.c      | 5 +----
>   3 files changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
> index 9b4df6eaa11a..a617fd360023 100644
> --- a/arch/x86/include/asm/kvm_para.h
> +++ b/arch/x86/include/asm/kvm_para.h
> @@ -6,8 +6,6 @@
>   #include <asm/alternative.h>
>   #include <uapi/asm/kvm_para.h>
>   
> -extern void kvmclock_init(void);
> -
>   #ifdef CONFIG_KVM_GUEST
>   bool kvm_check_and_clear_guest_paused(void);
>   #else
> @@ -85,6 +83,8 @@ static inline long kvm_hypercall4(unsigned int nr, unsigned long p1,
>   }
>   
>   #ifdef CONFIG_KVM_GUEST
> +void kvmclock_init(void);
> +void kvmclock_disable(void);
>   bool kvm_para_available(void);
>   unsigned int kvm_arch_para_features(void);
>   unsigned int kvm_arch_para_hints(void);
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 82a2756e0ef8..d6f04d32dec0 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -436,6 +436,7 @@ static void kvm_guest_cpu_offline(void)
>   		wrmsrl(MSR_KVM_PV_EOI_EN, 0);
>   	kvm_pv_disable_apf();
>   	apf_task_wake_all();
> +	kvmclock_disable();
>   }
>   
>   static int kvm_cpu_online(unsigned int cpu)
> diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> index 904494b924c1..bd3962953f78 100644
> --- a/arch/x86/kernel/kvmclock.c
> +++ b/arch/x86/kernel/kvmclock.c
> @@ -214,11 +214,9 @@ static void kvm_crash_shutdown(struct pt_regs *regs)
>   }
>   #endif
>   
> -static void kvm_shutdown(void)
> +void kvmclock_disable(void)
>   {
>   	native_write_msr(msr_kvm_system_time, 0, 0);
> -	kvm_disable_steal_time();
> -	native_machine_shutdown();
>   }
>   
>   static void __init kvmclock_init_mem(void)
> @@ -346,7 +344,6 @@ void __init kvmclock_init(void)
>   #endif
>   	x86_platform.save_sched_clock_state = kvm_save_sched_clock_state;
>   	x86_platform.restore_sched_clock_state = kvm_restore_sched_clock_state;
> -	machine_ops.shutdown  = kvm_shutdown;
>   #ifdef CONFIG_KEXEC_CORE
>   	machine_ops.crash_shutdown  = kvm_crash_shutdown;
>   #endif
> 

Acked-by: Paolo Bonzini <pbonzini@redhat.com>