linux-kernel - [PATCH] KVM: VMX: fix crash cleanup when KVM wasn't used

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Date:   Wed,  1 Apr 2020 10:13:48 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Jim Mattson <jmattson@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] KVM: VMX: fix crash cleanup when KVM wasn't used

If KVM wasn't used at all before we crash the cleanup procedure fails with
 BUG: unable to handle page fault for address: ffffffffffffffc8
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 23215067 P4D 23215067 PUD 23217067 PMD 0
 Oops: 0000 [#8] SMP PTI
 CPU: 0 PID: 3542 Comm: bash Kdump: loaded Tainted: G      D           5.6.0-rc2+ #823
 RIP: 0010:crash_vmclear_local_loaded_vmcss.cold+0x19/0x51 [kvm_intel]

The root cause is that loaded_vmcss_on_cpu list is not yet initialized,
we initialize it in hardware_enable() but this only happens when we start
a VM.

Previously, we used to have a bitmap with enabled CPUs and that was
preventing [masking] the issue.

Initialized loaded_vmcss_on_cpu list earlier, right before we assign
crash_vmclear_loaded_vmcss pointer. blocked_vcpu_on_cpu list and
blocked_vcpu_on_cpu_lock are moved altogether for consistency.

Fixes: 31603d4fc2bb ("KVM: VMX: Always VMCLEAR in-use VMCSes during crash with kexec support")
Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 arch/x86/kvm/vmx/vmx.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 3aba51d782e2..39a5dde12b79 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2257,10 +2257,6 @@ static int hardware_enable(void)
 	    !hv_get_vp_assist_page(cpu))
 		return -EFAULT;
 
-	INIT_LIST_HEAD(&per_cpu(loaded_vmcss_on_cpu, cpu));
-	INIT_LIST_HEAD(&per_cpu(blocked_vcpu_on_cpu, cpu));
-	spin_lock_init(&per_cpu(blocked_vcpu_on_cpu_lock, cpu));
-
 	r = kvm_cpu_vmxon(phys_addr);
 	if (r)
 		return r;
@@ -8006,7 +8002,7 @@ module_exit(vmx_exit);
 
 static int __init vmx_init(void)
 {
-	int r;
+	int r, cpu;
 
 #if IS_ENABLED(CONFIG_HYPERV)
 	/*
@@ -8060,6 +8056,12 @@ static int __init vmx_init(void)
 		return r;
 	}
 
+	for_each_possible_cpu(cpu) {
+		INIT_LIST_HEAD(&per_cpu(loaded_vmcss_on_cpu, cpu));
+		INIT_LIST_HEAD(&per_cpu(blocked_vcpu_on_cpu, cpu));
+		spin_lock_init(&per_cpu(blocked_vcpu_on_cpu_lock, cpu));
+	}
+
 #ifdef CONFIG_KEXEC_CORE
 	rcu_assign_pointer(crash_vmclear_loaded_vmcss,
 			   crash_vmclear_local_loaded_vmcss);
-- 
2.25.1