linux-kernel - [PATCH v3] KVM: nVMX: Fix trying to cancel vmlauch/vmresume

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Date:   Mon, 21 Aug 2017 16:08:32 -0700
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: [PATCH v3] KVM: nVMX: Fix trying to cancel vmlauch/vmresume

From: Wanpeng Li <wanpeng.li@...mail.com>

------------[ cut here ]------------
WARNING: CPU: 7 PID: 3861 at /home/kernel/ssd/kvm/arch/x86/kvm//vmx.c:11299 nested_vmx_vmexit+0x176e/0x1980 [kvm_intel]
CPU: 7 PID: 3861 Comm: qemu-system-x86 Tainted: G        W  OE   4.13.0-rc4+ #11
RIP: 0010:nested_vmx_vmexit+0x176e/0x1980 [kvm_intel]
Call Trace:
 ? kvm_multiple_exception+0x149/0x170 [kvm]
 ? handle_emulation_failure+0x79/0x230 [kvm]
 ? load_vmcs12_host_state+0xa80/0xa80 [kvm_intel]
 ? check_chain_key+0x137/0x1e0
 ? reexecute_instruction.part.168+0x130/0x130 [kvm]
 nested_vmx_inject_exception_vmexit+0xb7/0x100 [kvm_intel]
 ? nested_vmx_inject_exception_vmexit+0xb7/0x100 [kvm_intel]
 vmx_queue_exception+0x197/0x300 [kvm_intel]
 kvm_arch_vcpu_ioctl_run+0x1b0c/0x2c90 [kvm]
 ? kvm_arch_vcpu_runnable+0x220/0x220 [kvm]
 ? preempt_count_sub+0x18/0xc0
 ? restart_apic_timer+0x17d/0x300 [kvm]
 ? kvm_lapic_restart_hv_timer+0x37/0x50 [kvm]
 ? kvm_arch_vcpu_load+0x1d8/0x350 [kvm]
 kvm_vcpu_ioctl+0x4e4/0x910 [kvm]
 ? kvm_vcpu_ioctl+0x4e4/0x910 [kvm]
 ? kvm_dev_ioctl+0xbe0/0xbe0 [kvm]

The flag "nested_run_pending", which can override the decision of which should run 
next, L1 or L2. nested_run_pending=1 means that we *must* run L2 next, not L1. This 
is necessary in particular when L1 did a VMLAUNCH of L2 and therefore expects L2 to 
be run (and perhaps be injected with an event it specified, etc.). Nested_run_pending 
is especially intended to avoid switching  to L1 in the injection decision-point.

I catch this in the queue exception path, this patch fixes it by running L2 next 
instead of L1 in the queue exception path and injecting the pending exception to 
L2 directly.

Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
---
v2 -> v3:
 * move the nested_run_pending to the else branch
v1 -> v2:
 * request an immediate VM exit from L2 and keep the exception for 
   L1 pending for a subsequent nested VM exit

 arch/x86/kvm/vmx.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index e398946..685f51e 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2488,6 +2488,10 @@ static int nested_vmx_check_exception(struct kvm_vcpu *vcpu)
 		}
 	} else {
 		unsigned long exit_qual = 0;
+
+		if (to_vmx(vcpu)->nested.nested_run_pending)
+			return 0;
+
 		if (nr == DB_VECTOR)
 			exit_qual = vcpu->arch.dr6;
 
-- 
2.7.4