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Date:	Thu, 17 Jul 2014 10:56:09 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Wanpeng Li <wanpeng.li@...ux.intel.com>,
	Jan Kiszka <jan.kiszka@...mens.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	Gleb Natapov <gleb@...nel.org>, Bandan Das <bsd@...hat.com>,
	Zhang Yang <yang.z.zhang@...el.com>,
	Hu Robert <robert.hu@...el.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] KVM: nVMX: Fix vmptrld fail and vmwrite error when
 L1 goes down

Il 17/07/2014 06:56, Wanpeng Li ha scritto:
> This bug can be trigger by L1 goes down directly w/ enable_shadow_vmcs.
>
> [ 6413.158950] kvm: vmptrld           (null)/780000000000 failed
> [ 6413.158954] vmwrite error: reg 401e value 4 (err 1)
> [ 6413.158957] CPU: 0 PID: 4840 Comm: qemu-system-x86 Tainted: G           OE 3.16.0kvm+ #2
> [ 6413.158958] Hardware name: Dell Inc. OptiPlex 9020/0DNKMN, BIOS A05 12/05/2013
> [ 6413.158959]  0000000000000003 ffff880210c9fb58 ffffffff81741de9 ffff8800d7433f80
> [ 6413.158960]  ffff880210c9fb68 ffffffffa059fa08 ffff880210c9fb78 ffffffffa05938bf
> [ 6413.158962]  ffff880210c9fba8 ffffffffa059a97f ffff8800d7433f80 0000000000000003
> [ 6413.158963] Call Trace:
> [ 6413.158968]  [<ffffffff81741de9>] dump_stack+0x45/0x56
> [ 6413.158972]  [<ffffffffa059fa08>] vmwrite_error+0x2c/0x2e [kvm_intel]
> [ 6413.158974]  [<ffffffffa05938bf>] vmcs_writel+0x1f/0x30 [kvm_intel]
> [ 6413.158976]  [<ffffffffa059a97f>] free_nested.part.73+0x5f/0x170 [kvm_intel]
> [ 6413.158978]  [<ffffffffa059ab13>] vmx_free_vcpu+0x33/0x70 [kvm_intel]
> [ 6413.158991]  [<ffffffffa0360324>] kvm_arch_vcpu_free+0x44/0x50 [kvm]
> [ 6413.158998]  [<ffffffffa0360f92>] kvm_arch_destroy_vm+0xf2/0x1f0 [kvm]
>
> Commit 26a865 (KVM: VMX: fix use after free of vmx->loaded_vmcs) fix the use
> after free bug by move free_loaded_vmcs() before free_nested(), however, this
> lead to free loaded_vmcs->vmcs premature and vmptrld load a NULL pointer during
> sync shadow vmcs to vmcs12. In addition, vmwrite which used to disable shadow
> vmcs and reset VMCS_LINK_POINTER failed since there is no valid current-VMCS.
> This patch fix it by skipping sync shadow vmcs and reset vmcs field for L1
> destroy since they will be reinitialized after L1 recreate.
>
> Signed-off-by: Wanpeng Li <wanpeng.li@...ux.intel.com>
> ---
>  arch/x86/kvm/vmx.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index fbce89e..2b28da7 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -6113,9 +6113,9 @@ static void free_nested(struct vcpu_vmx *vmx)
>  		return;
>  	vmx->nested.vmxon = false;
>  	if (vmx->nested.current_vmptr != -1ull) {
> -		nested_release_vmcs12(vmx);
>  		vmx->nested.current_vmptr = -1ull;
>  		vmx->nested.current_vmcs12 = NULL;
> +		nested_release_vmcs12(vmx);
>  	}
>  	if (enable_shadow_vmcs)
>  		free_vmcs(vmx->nested.current_shadow_vmcs);
>

This looks good, I'll apply it to kvm/master.

Paolo
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