diff options
| author | Wanpeng Li <wanpeng.li@hotmail.com> | 2017-05-11 18:12:05 -0700 |
|---|---|---|
| committer | Radim Krčmář <rkrcmar@redhat.com> | 2017-05-19 19:59:25 +0200 |
| commit | e2c2206a18993bc9f62393d49c7b2066c3845b25 (patch) | |
| tree | eef60b936ce03eda0fc6b8eb2d7040ee574270be | |
| parent | d3e7dec054174fdddae33eaa0032a82c3f42181d (diff) | |
KVM: x86: Fix potential preemption when get the current kvmclock timestamp
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>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
| -rw-r--r-- | arch/x86/kvm/x86.c | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index b54125b590e8..3b5fc7e35f6e 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) |