[PATCH v3] KVM: x86: Fix potential preemption when get the current kvmclock timestamp

[PATCH v3] KVM: x86: Fix potential preemption when get the current kvmclock timestamp

[Wanpeng Li]

From: Wanpeng Li <wanpeng.li@hotmail.com>

 BUG: using __this_cpu_read() in preemptible [00000000] code: qemu-system-x86/2809
 caller is __this_cpu_preempt_check+0x13/0x20
 CPU: 2 PID: 2809 Comm: qemu-system-x86 Not tainted 4.11.0+ #13
 Call Trace:
  dump_stack+0x99/0xce
  check_preemption_disabled+0xf5/0x100
  __this_cpu_preempt_check+0x13/0x20
  get_kvmclock_ns+0x6f/0x110 [kvm]
  get_time_ref_counter+0x5d/0x80 [kvm]
  kvm_hv_process_stimers+0x2a1/0x8a0 [kvm]
  ? kvm_hv_process_stimers+0x2a1/0x8a0 [kvm]
  ? kvm_arch_vcpu_ioctl_run+0xac9/0x1ce0 [kvm]
  kvm_arch_vcpu_ioctl_run+0x5bf/0x1ce0 [kvm]
  kvm_vcpu_ioctl+0x384/0x7b0 [kvm]
  ? kvm_vcpu_ioctl+0x384/0x7b0 [kvm]
  ? __fget+0xf3/0x210
  do_vfs_ioctl+0xa4/0x700
  ? __fget+0x114/0x210
  SyS_ioctl+0x79/0x90
  entry_SYSCALL_64_fastpath+0x23/0xc2
 RIP: 0033:0x7f9d164ed357
  ? __this_cpu_preempt_check+0x13/0x20

This can be reproduced by run kvm-unit-tests/hyperv_stimer.flat w/ 
CONFIG_PREEMPT and CONFIG_DEBUG_PREEMPT enabled.

Safe access to per-CPU data requires a couple of constraints, though: the 
thread working with the data cannot be preempted and it cannot be migrated 
while it manipulates per-CPU variables. If the thread is preempted, the 
thread that replaces it could try to work with the same variables; migration 
to another CPU could also cause confusion. However there is no preemption 
disable when reads host per-CPU tsc rate to calculate the current kvmclock 
timestamp.

This patch fixes it by utilizing get_cpu/put_cpu pair to guarantee both 
__this_cpu_read() and rdtsc() are not preempted.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
v2 -> v3:
 * update patch description
v1 -> v2:
 * utilize get_cpu/put_cpu pair to protect both __this_cpu_read and rdtsc()

 arch/x86/kvm/x86.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b54125b..3b5fc7e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1763,6 +1763,7 @@ u64 get_kvmclock_ns(struct kvm *kvm)
 {
 	struct kvm_arch *ka = &kvm->arch;
 	struct pvclock_vcpu_time_info hv_clock;
+	u64 ret;
 
 	spin_lock(&ka->pvclock_gtod_sync_lock);
 	if (!ka->use_master_clock) {
@@ -1774,10 +1775,17 @@ u64 get_kvmclock_ns(struct kvm *kvm)
 	hv_clock.system_time = ka->master_kernel_ns + ka->kvmclock_offset;
 	spin_unlock(&ka->pvclock_gtod_sync_lock);
 
+	/* both __this_cpu_read() and rdtsc() should be on the same cpu */
+	get_cpu();
+
 	kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL,
 			   &hv_clock.tsc_shift,
 			   &hv_clock.tsc_to_system_mul);
-	return __pvclock_read_cycles(&hv_clock, rdtsc());
+	ret = __pvclock_read_cycles(&hv_clock, rdtsc());
+
+	put_cpu();
+
+	return ret;
 }
 
 static void kvm_setup_pvclock_page(struct kvm_vcpu *v)
-- 
2.7.4

Re: [PATCH v3] KVM: x86: Fix potential preemption when get the current kvmclock timestamp

[Paolo Bonzini]

On 12/05/2017 03:12, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@hotmail.com>
> 
>  BUG: using __this_cpu_read() in preemptible [00000000] code: qemu-system-x86/2809
>  caller is __this_cpu_preempt_check+0x13/0x20
>  CPU: 2 PID: 2809 Comm: qemu-system-x86 Not tainted 4.11.0+ #13
>  Call Trace:
>   dump_stack+0x99/0xce
>   check_preemption_disabled+0xf5/0x100
>   __this_cpu_preempt_check+0x13/0x20
>   get_kvmclock_ns+0x6f/0x110 [kvm]
>   get_time_ref_counter+0x5d/0x80 [kvm]
>   kvm_hv_process_stimers+0x2a1/0x8a0 [kvm]
>   ? kvm_hv_process_stimers+0x2a1/0x8a0 [kvm]
>   ? kvm_arch_vcpu_ioctl_run+0xac9/0x1ce0 [kvm]
>   kvm_arch_vcpu_ioctl_run+0x5bf/0x1ce0 [kvm]
>   kvm_vcpu_ioctl+0x384/0x7b0 [kvm]
>   ? kvm_vcpu_ioctl+0x384/0x7b0 [kvm]
>   ? __fget+0xf3/0x210
>   do_vfs_ioctl+0xa4/0x700
>   ? __fget+0x114/0x210
>   SyS_ioctl+0x79/0x90
>   entry_SYSCALL_64_fastpath+0x23/0xc2
>  RIP: 0033:0x7f9d164ed357
>   ? __this_cpu_preempt_check+0x13/0x20
> 
> This can be reproduced by run kvm-unit-tests/hyperv_stimer.flat w/ 
> CONFIG_PREEMPT and CONFIG_DEBUG_PREEMPT enabled.
> 
> Safe access to per-CPU data requires a couple of constraints, though: the 
> thread working with the data cannot be preempted and it cannot be migrated 
> while it manipulates per-CPU variables. If the thread is preempted, the 
> thread that replaces it could try to work with the same variables; migration 
> to another CPU could also cause confusion. However there is no preemption 
> disable when reads host per-CPU tsc rate to calculate the current kvmclock 
> timestamp.
> 
> This patch fixes it by utilizing get_cpu/put_cpu pair to guarantee both 
> __this_cpu_read() and rdtsc() are not preempted.
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
> ---
> v2 -> v3:
>  * update patch description
> v1 -> v2:
>  * utilize get_cpu/put_cpu pair to protect both __this_cpu_read and rdtsc()
> 
>  arch/x86/kvm/x86.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b54125b..3b5fc7e 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1763,6 +1763,7 @@ u64 get_kvmclock_ns(struct kvm *kvm)
>  {
>  	struct kvm_arch *ka = &kvm->arch;
>  	struct pvclock_vcpu_time_info hv_clock;
> +	u64 ret;
>  
>  	spin_lock(&ka->pvclock_gtod_sync_lock);
>  	if (!ka->use_master_clock) {
> @@ -1774,10 +1775,17 @@ u64 get_kvmclock_ns(struct kvm *kvm)
>  	hv_clock.system_time = ka->master_kernel_ns + ka->kvmclock_offset;
>  	spin_unlock(&ka->pvclock_gtod_sync_lock);
>  
> +	/* both __this_cpu_read() and rdtsc() should be on the same cpu */
> +	get_cpu();
> +
>  	kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL,
>  			   &hv_clock.tsc_shift,
>  			   &hv_clock.tsc_to_system_mul);
> -	return __pvclock_read_cycles(&hv_clock, rdtsc());
> +	ret = __pvclock_read_cycles(&hv_clock, rdtsc());
> +
> +	put_cpu();
> +
> +	return ret;
>  }
>  
>  static void kvm_setup_pvclock_page(struct kvm_vcpu *v)
> 

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: stable@vger.kernel.org

Re: [PATCH v3] KVM: x86: Fix potential preemption when get the current kvmclock timestamp

[Wanpeng Li]

Ping,
2017-05-12 15:44 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>:
>
>
> On 12/05/2017 03:12, Wanpeng Li wrote:
>> From: Wanpeng Li <wanpeng.li@hotmail.com>
>>
>>  BUG: using __this_cpu_read() in preemptible [00000000] code: qemu-system-x86/2809
>>  caller is __this_cpu_preempt_check+0x13/0x20
>>  CPU: 2 PID: 2809 Comm: qemu-system-x86 Not tainted 4.11.0+ #13
>>  Call Trace:
>>   dump_stack+0x99/0xce
>>   check_preemption_disabled+0xf5/0x100
>>   __this_cpu_preempt_check+0x13/0x20
>>   get_kvmclock_ns+0x6f/0x110 [kvm]
>>   get_time_ref_counter+0x5d/0x80 [kvm]
>>   kvm_hv_process_stimers+0x2a1/0x8a0 [kvm]
>>   ? kvm_hv_process_stimers+0x2a1/0x8a0 [kvm]
>>   ? kvm_arch_vcpu_ioctl_run+0xac9/0x1ce0 [kvm]
>>   kvm_arch_vcpu_ioctl_run+0x5bf/0x1ce0 [kvm]
>>   kvm_vcpu_ioctl+0x384/0x7b0 [kvm]
>>   ? kvm_vcpu_ioctl+0x384/0x7b0 [kvm]
>>   ? __fget+0xf3/0x210
>>   do_vfs_ioctl+0xa4/0x700
>>   ? __fget+0x114/0x210
>>   SyS_ioctl+0x79/0x90
>>   entry_SYSCALL_64_fastpath+0x23/0xc2
>>  RIP: 0033:0x7f9d164ed357
>>   ? __this_cpu_preempt_check+0x13/0x20
>>
>> This can be reproduced by run kvm-unit-tests/hyperv_stimer.flat w/
>> CONFIG_PREEMPT and CONFIG_DEBUG_PREEMPT enabled.
>>
>> Safe access to per-CPU data requires a couple of constraints, though: the
>> thread working with the data cannot be preempted and it cannot be migrated
>> while it manipulates per-CPU variables. If the thread is preempted, the
>> thread that replaces it could try to work with the same variables; migration
>> to another CPU could also cause confusion. However there is no preemption
>> disable when reads host per-CPU tsc rate to calculate the current kvmclock
>> timestamp.
>>
>> This patch fixes it by utilizing get_cpu/put_cpu pair to guarantee both
>> __this_cpu_read() and rdtsc() are not preempted.
>>
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> Cc: Radim Krčmář <rkrcmar@redhat.com>
>> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
>> ---
>> v2 -> v3:
>>  * update patch description
>> v1 -> v2:
>>  * utilize get_cpu/put_cpu pair to protect both __this_cpu_read and rdtsc()
>>
>>  arch/x86/kvm/x86.c | 10 +++++++++-
>>  1 file changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index b54125b..3b5fc7e 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -1763,6 +1763,7 @@ u64 get_kvmclock_ns(struct kvm *kvm)
>>  {
>>       struct kvm_arch *ka = &kvm->arch;
>>       struct pvclock_vcpu_time_info hv_clock;
>> +     u64 ret;
>>
>>       spin_lock(&ka->pvclock_gtod_sync_lock);
>>       if (!ka->use_master_clock) {
>> @@ -1774,10 +1775,17 @@ u64 get_kvmclock_ns(struct kvm *kvm)
>>       hv_clock.system_time = ka->master_kernel_ns + ka->kvmclock_offset;
>>       spin_unlock(&ka->pvclock_gtod_sync_lock);
>>
>> +     /* both __this_cpu_read() and rdtsc() should be on the same cpu */
>> +     get_cpu();
>> +
>>       kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL,
>>                          &hv_clock.tsc_shift,
>>                          &hv_clock.tsc_to_system_mul);
>> -     return __pvclock_read_cycles(&hv_clock, rdtsc());
>> +     ret = __pvclock_read_cycles(&hv_clock, rdtsc());
>> +
>> +     put_cpu();
>> +
>> +     return ret;
>>  }
>>
>>  static void kvm_setup_pvclock_page(struct kvm_vcpu *v)
>>
>
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> Cc: stable@vger.kernel.org

Re: [PATCH v3] KVM: x86: Fix potential preemption when get the current kvmclock timestamp

[Radim Krčmář]

2017-05-19 05:53+0800, Wanpeng Li:
> Ping,

Applying for 4.12-rc2, thanks.