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Subject: Re: [PATCH 4/4] KVM: nVMX: Fix using __this_cpu_read() in preemptible
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To:     Wanpeng Li <kernellwp@gmail.com>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Cc:     =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>
References: <1558082990-7822-1-git-send-email-wanpengli@tencent.com>
 <1558082990-7822-4-git-send-email-wanpengli@tencent.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <4874aa09-7f46-7ca5-5d32-1d7b1cb1eef3@redhat.com>
Date:   Mon, 20 May 2019 12:36:37 +0200
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On 17/05/19 10:49, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@tencent.com>
> 
>  BUG: using __this_cpu_read() in preemptible [00000000] code: qemu-system-x86/4590
>   caller is nested_vmx_enter_non_root_mode+0xebd/0x1790 [kvm_intel]
>   CPU: 4 PID: 4590 Comm: qemu-system-x86 Tainted: G           OE     5.1.0-rc4+ #1
>   Call Trace:
>    dump_stack+0x67/0x95
>    __this_cpu_preempt_check+0xd2/0xe0
>    nested_vmx_enter_non_root_mode+0xebd/0x1790 [kvm_intel]
>    nested_vmx_run+0xda/0x2b0 [kvm_intel]
>    handle_vmlaunch+0x13/0x20 [kvm_intel]
>    vmx_handle_exit+0xbd/0x660 [kvm_intel]
>    kvm_arch_vcpu_ioctl_run+0xa2c/0x1e50 [kvm]
>    kvm_vcpu_ioctl+0x3ad/0x6d0 [kvm]
>    do_vfs_ioctl+0xa5/0x6e0
>    ksys_ioctl+0x6d/0x80
>    __x64_sys_ioctl+0x1a/0x20
>    do_syscall_64+0x6f/0x6c0
>    entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> Accessing per-cpu variable should disable preemption, this patch extends the 
> preemption disable region for __this_cpu_read().
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
>  arch/x86/kvm/vmx/nested.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 0c601d0..8f6f69c 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -2792,14 +2792,13 @@ static int nested_vmx_check_vmentry_hw(struct kvm_vcpu *vcpu)
>  	      : "cc", "memory"
>  	);
>  
> -	preempt_enable();
> -
>  	if (vmx->msr_autoload.host.nr)
>  		vmcs_write32(VM_EXIT_MSR_LOAD_COUNT, vmx->msr_autoload.host.nr);
>  	if (vmx->msr_autoload.guest.nr)
>  		vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, vmx->msr_autoload.guest.nr);
>  
>  	if (vm_fail) {
> +		preempt_enable();
>  		WARN_ON_ONCE(vmcs_read32(VM_INSTRUCTION_ERROR) !=
>  			     VMXERR_ENTRY_INVALID_CONTROL_FIELD);
>  		return 1;
> @@ -2811,6 +2810,7 @@ static int nested_vmx_check_vmentry_hw(struct kvm_vcpu *vcpu)
>  	local_irq_enable();
>  	if (hw_breakpoint_active())
>  		set_debugreg(__this_cpu_read(cpu_dr7), 7);
> +	preempt_enable();
>  
>  	/*
>  	 * A non-failing VMEntry means we somehow entered guest mode with
> 


Queued, thanks.

Paolo