92 lines
3.2 KiB
Diff
92 lines
3.2 KiB
Diff
From f944a307041bf3d43dbc9ca3484982dfec4340f5 Mon Sep 17 00:00:00 2001
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From: Wanpeng Li <wanpeng.li@hotmail.com>
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Date: Thu, 11 May 2017 18:12:05 -0700
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Subject: [PATCH 1/1] KVM: x86: Fix potential preemption when get the current
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kvmclock timestamp
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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BUG: using __this_cpu_read() in preemptible [00000000] code: qemu-system-x86/2809
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caller is __this_cpu_preempt_check+0x13/0x20
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CPU: 2 PID: 2809 Comm: qemu-system-x86 Not tainted 4.11.0+ #13
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Call Trace:
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dump_stack+0x99/0xce
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check_preemption_disabled+0xf5/0x100
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__this_cpu_preempt_check+0x13/0x20
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get_kvmclock_ns+0x6f/0x110 [kvm]
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get_time_ref_counter+0x5d/0x80 [kvm]
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kvm_hv_process_stimers+0x2a1/0x8a0 [kvm]
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? kvm_hv_process_stimers+0x2a1/0x8a0 [kvm]
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? kvm_arch_vcpu_ioctl_run+0xac9/0x1ce0 [kvm]
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kvm_arch_vcpu_ioctl_run+0x5bf/0x1ce0 [kvm]
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kvm_vcpu_ioctl+0x384/0x7b0 [kvm]
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? kvm_vcpu_ioctl+0x384/0x7b0 [kvm]
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? __fget+0xf3/0x210
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do_vfs_ioctl+0xa4/0x700
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? __fget+0x114/0x210
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SyS_ioctl+0x79/0x90
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entry_SYSCALL_64_fastpath+0x23/0xc2
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RIP: 0033:0x7f9d164ed357
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? __this_cpu_preempt_check+0x13/0x20
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This can be reproduced by run kvm-unit-tests/hyperv_stimer.flat w/
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CONFIG_PREEMPT and CONFIG_DEBUG_PREEMPT enabled.
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Safe access to per-CPU data requires a couple of constraints, though: the
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thread working with the data cannot be preempted and it cannot be migrated
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while it manipulates per-CPU variables. If the thread is preempted, the
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thread that replaces it could try to work with the same variables; migration
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to another CPU could also cause confusion. However there is no preemption
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disable when reads host per-CPU tsc rate to calculate the current kvmclock
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timestamp.
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This patch fixes it by utilizing get_cpu/put_cpu pair to guarantee both
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__this_cpu_read() and rdtsc() are not preempted.
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Cc: Paolo Bonzini <pbonzini@redhat.com>
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Cc: Radim Krčmář <rkrcmar@redhat.com>
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Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
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Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
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Cc: stable@vger.kernel.org
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Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
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Signed-off-by: Alex Kozyrev <alex.kozyrev@windriver.com>
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---
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arch/x86/kvm/x86.c | 10 +++++++++-
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1 file changed, 9 insertions(+), 1 deletion(-)
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diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
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index 8babcb5..84925dc 100644
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--- a/arch/x86/kvm/x86.c
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+++ b/arch/x86/kvm/x86.c
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@@ -1743,6 +1743,7 @@ u64 get_kvmclock_ns(struct kvm *kvm)
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{
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struct kvm_arch *ka = &kvm->arch;
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struct pvclock_vcpu_time_info hv_clock;
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+ u64 ret;
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spin_lock(&ka->pvclock_gtod_sync_lock);
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if (!ka->use_master_clock) {
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@@ -1753,10 +1754,17 @@ u64 get_kvmclock_ns(struct kvm *kvm)
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hv_clock.system_time = ka->master_kernel_ns + ka->kvmclock_offset;
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spin_unlock(&ka->pvclock_gtod_sync_lock);
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+ /* both __this_cpu_read() and rdtsc() should be on the same cpu */
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+ get_cpu();
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+
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kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL,
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&hv_clock.tsc_shift,
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&hv_clock.tsc_to_system_mul);
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- return __pvclock_read_cycles(&hv_clock, rdtsc());
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+ ret = __pvclock_read_cycles(&hv_clock, rdtsc());
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+
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+ put_cpu();
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+
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+ return ret;
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}
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static int kvm_guest_time_update(struct kvm_vcpu *v)
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--
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1.8.3.1
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