linux-kernel - Re: [PATCH] KVM: nVMX: Fix reload apic access page warning

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Date:   Fri, 23 Sep 2016 01:10:15 +0200
From:   Radim Krčmář <rkrcmar@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Yunhong Jiang <yunhong.jiang@...el.com>
Subject: Re: [PATCH] KVM: nVMX: Fix reload apic access page warning

2016-09-06 17:20+0800, Wanpeng Li:
> From: Wanpeng Li <wanpeng.li@...mail.com>
> WARNING: CPU: 1 PID: 4230 at kernel/sched/core.c:7564 __might_sleep+0x7e/0x80
> do not call blocking ops when !TASK_RUNNING; state=1 set at [<ffffffff8d0de7f9>] prepare_to_swait+0x39/0xa0
> CPU: 1 PID: 4230 Comm: qemu-system-x86 Not tainted 4.8.0-rc5+ #47
> Call Trace:
>  dump_stack+0x99/0xd0
>  __warn+0xd1/0xf0
>  warn_slowpath_fmt+0x4f/0x60
>  ? prepare_to_swait+0x39/0xa0
>  ? prepare_to_swait+0x39/0xa0
>  __might_sleep+0x7e/0x80
>  __gfn_to_pfn_memslot+0x156/0x480 [kvm]
>  gfn_to_pfn+0x2a/0x30 [kvm]
>  gfn_to_page+0xe/0x20 [kvm]
>  kvm_vcpu_reload_apic_access_page+0x32/0xa0 [kvm]
>  nested_vmx_vmexit+0x765/0xca0 [kvm_intel]
>  ? _raw_spin_unlock_irqrestore+0x36/0x80
>  vmx_check_nested_events+0x49/0x1f0 [kvm_intel]
>  kvm_arch_vcpu_runnable+0x2d/0xe0 [kvm]
>  kvm_vcpu_check_block+0x12/0x60 [kvm]
>  kvm_vcpu_block+0x94/0x4c0 [kvm]
>  kvm_arch_vcpu_ioctl_run+0x619/0x1aa0 [kvm]
>  ? kvm_arch_vcpu_ioctl_run+0xdf1/0x1aa0 [kvm]
>  kvm_vcpu_ioctl+0x2d3/0x7c0 [kvm]
> 
> ===============================
> [ INFO: suspicious RCU usage. ]
> 4.8.0-rc5+ #47 Not tainted
> -------------------------------
> ./include/linux/kvm_host.h:535 suspicious rcu_dereference_check() usage!
> 
> other info that might help us debug this:
> 
> 
> rcu_scheduler_active = 1, debug_locks = 0
> 1 lock held by qemu-system-x86/4230:
>  #0:  (&vcpu->mutex){+.+.+.}, at: [<ffffffffc062975c>] vcpu_load+0x1c/0x60 [kvm]
> 
> stack backtrace:
> CPU: 1 PID: 4230 Comm: qemu-system-x86 Not tainted 4.8.0-rc5+ #47
> Call Trace:
>  dump_stack+0x99/0xd0
>  lockdep_rcu_suspicious+0xe7/0x120
>  gfn_to_memslot+0x12a/0x140 [kvm]
>  gfn_to_pfn+0x12/0x30 [kvm]
>  gfn_to_page+0xe/0x20 [kvm]
>  kvm_vcpu_reload_apic_access_page+0x32/0xa0 [kvm]
>  nested_vmx_vmexit+0x765/0xca0 [kvm_intel]
>  ? _raw_spin_unlock_irqrestore+0x36/0x80
>  vmx_check_nested_events+0x49/0x1f0 [kvm_intel]
>  kvm_arch_vcpu_runnable+0x2d/0xe0 [kvm]
>  kvm_vcpu_check_block+0x12/0x60 [kvm]
>  kvm_vcpu_block+0x94/0x4c0 [kvm]
>  kvm_arch_vcpu_ioctl_run+0x619/0x1aa0 [kvm]
>  ? kvm_arch_vcpu_ioctl_run+0xdf1/0x1aa0 [kvm]
>  kvm_vcpu_ioctl+0x2d3/0x7c0 [kvm]
>  ? __fget+0xfd/0x210
>  ? __lock_is_held+0x54/0x70
>  do_vfs_ioctl+0x96/0x6a0
>  ? __fget+0x11c/0x210
>  ? __fget+0x5/0x210
>  SyS_ioctl+0x79/0x90
>  do_syscall_64+0x81/0x220
>  entry_SYSCALL64_slow_path+0x25/0x25
> 
> These can be triggered by running kvm-unit-test: ./x86-run x86/vmx.flat
> 
> The nested preemption timer is based on hrtimer which is started on L2 
> entry, stopped on L2 exit and evaluated via the new check_nested_events 
> hook. The current logic adds vCPU to a simple waitqueue (TASK_INTERRUPTIBLE) 
> if need to yield pCPU and w/o holding srcu read lock when accesses memslots, 
> both can be in nested preemption timer evaluation path which results in 
> the warning above. 
> 
> This patch fix it by leveraging request bit to async reload APIC access 
> page before vmentry in order to avoid to reload directly during the nested 
> preemption timer evaluation, it is safe since the vmcs01 is loaded and 
> current is nested vmexit.
> 
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Cc: Yunhong Jiang <yunhong.jiang@...el.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
> ---

Applied to kvm/queue, thanks.