linux-kernel - [PATCH 3/3] KVM: nVMX: Fix vmptrld fail and vmwrite error when L1 goes down

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Date:	Thu, 17 Jul 2014 12:56:51 +0800
From:	Wanpeng Li <wanpeng.li@...ux.intel.com>
To:	Paolo Bonzini <pbonzini@...hat.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,
	Wanpeng Li <wanpeng.li@...ux.intel.com>
Subject: [PATCH 3/3] KVM: nVMX: Fix vmptrld fail and vmwrite error when L1 goes down 

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);
-- 
1.9.1

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