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authorWanpeng Li <wanpeng.li@hotmail.com>2017-05-11 18:12:05 -0700
committerRadim Krčmář <rkrcmar@redhat.com>2017-05-19 19:59:25 +0200
commite2c2206a18993bc9f62393d49c7b2066c3845b25 (patch)
treeeef60b936ce03eda0fc6b8eb2d7040ee574270be
parentd3e7dec054174fdddae33eaa0032a82c3f42181d (diff)
downloadlinux-e2c2206a18993bc9f62393d49c7b2066c3845b25.tar.bz2
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.c10
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)