* [PATCH] KVM: x86: Fix potential preemption when get the current kvmclock timestamp
@ 2017-05-11 12:00 Wanpeng Li
2017-05-11 12:10 ` Paolo Bonzini
0 siblings, 1 reply; 4+ messages in thread
From: Wanpeng Li @ 2017-05-11 12:00 UTC (permalink / raw)
To: linux-kernel, kvm; +Cc: Paolo Bonzini, Radim Krčmář, 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
RSP: 002b:00007f9d0f6768f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: ffffffffa64d53c3 RCX: 00007f9d164ed357
RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 000000000000000d
RBP: ffffbb260856bf88 R08: 0000556b2a13eeb0 R09: 0000000000000000
R10: 00007f9d080000c8 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9d1853d000 R14: 0000000000000000 R15: 000000000000ae80
? __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 fix it by holding pvclock_gtod_sync_lock lock when calculates
pvclock's time scale in order to disable preemption for host per-CPU tsc
rate read.
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
arch/x86/kvm/x86.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b54125b..8008d56 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1772,11 +1772,11 @@ u64 get_kvmclock_ns(struct kvm *kvm)
hv_clock.tsc_timestamp = ka->master_cycle_now;
hv_clock.system_time = ka->master_kernel_ns + ka->kvmclock_offset;
- spin_unlock(&ka->pvclock_gtod_sync_lock);
kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL,
&hv_clock.tsc_shift,
&hv_clock.tsc_to_system_mul);
+ spin_unlock(&ka->pvclock_gtod_sync_lock);
return __pvclock_read_cycles(&hv_clock, rdtsc());
}
--
2.7.4
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] KVM: x86: Fix potential preemption when get the current kvmclock timestamp
2017-05-11 12:00 [PATCH] KVM: x86: Fix potential preemption when get the current kvmclock timestamp Wanpeng Li
@ 2017-05-11 12:10 ` Paolo Bonzini
2017-05-11 12:15 ` Wanpeng Li
0 siblings, 1 reply; 4+ messages in thread
From: Paolo Bonzini @ 2017-05-11 12:10 UTC (permalink / raw)
To: Wanpeng Li, linux-kernel, kvm; +Cc: Radim Krčmář, Wanpeng Li
On 11/05/2017 14:00, 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
> RSP: 002b:00007f9d0f6768f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: ffffffffa64d53c3 RCX: 00007f9d164ed357
> RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 000000000000000d
> RBP: ffffbb260856bf88 R08: 0000556b2a13eeb0 R09: 0000000000000000
> R10: 00007f9d080000c8 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f9d1853d000 R14: 0000000000000000 R15: 000000000000ae80
> ? __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 fix it by holding pvclock_gtod_sync_lock lock when calculates
> pvclock's time scale in order to disable preemption for host per-CPU tsc
> rate read.
>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
> ---
> arch/x86/kvm/x86.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b54125b..8008d56 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1772,11 +1772,11 @@ u64 get_kvmclock_ns(struct kvm *kvm)
>
> hv_clock.tsc_timestamp = ka->master_cycle_now;
> hv_clock.system_time = ka->master_kernel_ns + ka->kvmclock_offset;
> - spin_unlock(&ka->pvclock_gtod_sync_lock);
>
> kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL,
> &hv_clock.tsc_shift,
> &hv_clock.tsc_to_system_mul);
> + spin_unlock(&ka->pvclock_gtod_sync_lock);
> return __pvclock_read_cycles(&hv_clock, rdtsc());
> }
>
>
This would not be enough for PREEMPT_RT. You need to use
get_cpu/put_cpu (including __pvclock_read_cycles in the non-preemptable
section).
Thanks,
Paolo
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] KVM: x86: Fix potential preemption when get the current kvmclock timestamp
2017-05-11 12:10 ` Paolo Bonzini
@ 2017-05-11 12:15 ` Wanpeng Li
2017-05-11 12:26 ` Paolo Bonzini
0 siblings, 1 reply; 4+ messages in thread
From: Wanpeng Li @ 2017-05-11 12:15 UTC (permalink / raw)
To: Paolo Bonzini; +Cc: linux-kernel, kvm, Radim Krčmář, Wanpeng Li
2017-05-11 20:10 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>:
>
>
> On 11/05/2017 14:00, 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
>> RSP: 002b:00007f9d0f6768f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
>> RAX: ffffffffffffffda RBX: ffffffffa64d53c3 RCX: 00007f9d164ed357
>> RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 000000000000000d
>> RBP: ffffbb260856bf88 R08: 0000556b2a13eeb0 R09: 0000000000000000
>> R10: 00007f9d080000c8 R11: 0000000000000246 R12: 0000000000000000
>> R13: 00007f9d1853d000 R14: 0000000000000000 R15: 000000000000ae80
>> ? __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 fix it by holding pvclock_gtod_sync_lock lock when calculates
>> pvclock's time scale in order to disable preemption for host per-CPU tsc
>> rate read.
>>
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> Cc: Radim Krčmář <rkrcmar@redhat.com>
>> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
>> ---
>> arch/x86/kvm/x86.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index b54125b..8008d56 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -1772,11 +1772,11 @@ u64 get_kvmclock_ns(struct kvm *kvm)
>>
>> hv_clock.tsc_timestamp = ka->master_cycle_now;
>> hv_clock.system_time = ka->master_kernel_ns + ka->kvmclock_offset;
>> - spin_unlock(&ka->pvclock_gtod_sync_lock);
>>
>> kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL,
>> &hv_clock.tsc_shift,
>> &hv_clock.tsc_to_system_mul);
>> + spin_unlock(&ka->pvclock_gtod_sync_lock);
>> return __pvclock_read_cycles(&hv_clock, rdtsc());
>> }
>>
>>
>
> This would not be enough for PREEMPT_RT. You need to use
> get_cpu/put_cpu (including __pvclock_read_cycles in the non-preemptable
> section).
Actually the splat is for __this_cpu_read(cpu_tsc_khz), so I just protect it.
Regards,
Wanpeng Li
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] KVM: x86: Fix potential preemption when get the current kvmclock timestamp
2017-05-11 12:15 ` Wanpeng Li
@ 2017-05-11 12:26 ` Paolo Bonzini
0 siblings, 0 replies; 4+ messages in thread
From: Paolo Bonzini @ 2017-05-11 12:26 UTC (permalink / raw)
To: Wanpeng Li; +Cc: linux-kernel, kvm, Radim Krčmář, Wanpeng Li
On 11/05/2017 14:15, Wanpeng Li wrote:
> 2017-05-11 20:10 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>:
>>
>>
>> On 11/05/2017 14:00, 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
>>> RSP: 002b:00007f9d0f6768f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
>>> RAX: ffffffffffffffda RBX: ffffffffa64d53c3 RCX: 00007f9d164ed357
>>> RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 000000000000000d
>>> RBP: ffffbb260856bf88 R08: 0000556b2a13eeb0 R09: 0000000000000000
>>> R10: 00007f9d080000c8 R11: 0000000000000246 R12: 0000000000000000
>>> R13: 00007f9d1853d000 R14: 0000000000000000 R15: 000000000000ae80
>>> ? __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 fix it by holding pvclock_gtod_sync_lock lock when calculates
>>> pvclock's time scale in order to disable preemption for host per-CPU tsc
>>> rate read.
>>>
>>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>>> Cc: Radim Krčmář <rkrcmar@redhat.com>
>>> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
>>> ---
>>> arch/x86/kvm/x86.c | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>> index b54125b..8008d56 100644
>>> --- a/arch/x86/kvm/x86.c
>>> +++ b/arch/x86/kvm/x86.c
>>> @@ -1772,11 +1772,11 @@ u64 get_kvmclock_ns(struct kvm *kvm)
>>>
>>> hv_clock.tsc_timestamp = ka->master_cycle_now;
>>> hv_clock.system_time = ka->master_kernel_ns + ka->kvmclock_offset;
>>> - spin_unlock(&ka->pvclock_gtod_sync_lock);
>>>
>>> kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL,
>>> &hv_clock.tsc_shift,
>>> &hv_clock.tsc_to_system_mul);
>>> + spin_unlock(&ka->pvclock_gtod_sync_lock);
>>> return __pvclock_read_cycles(&hv_clock, rdtsc());
>>> }
>>>
>>>
>>
>> This would not be enough for PREEMPT_RT. You need to use
>> get_cpu/put_cpu (including __pvclock_read_cycles in the non-preemptable
>> section).
>
> Actually the splat is for __this_cpu_read(cpu_tsc_khz), so I just protect it.
Yes, but spin_lock/spin_unlock would still be preemptable on PREEMPT_RT.
Also, rdtsc() should really be on the same CPU as __this_cpu_read. We
know it's not really really necessary because the master clock is
active, but since we need a get_cpu/put_cpu pair, better be clean.
Paolo
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2017-05-11 12:26 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2017-05-11 12:00 [PATCH] KVM: x86: Fix potential preemption when get the current kvmclock timestamp Wanpeng Li
2017-05-11 12:10 ` Paolo Bonzini
2017-05-11 12:15 ` Wanpeng Li
2017-05-11 12:26 ` Paolo Bonzini
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