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

Vitaly Kuznetsov
2020-04-01T08:13:56Z

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@redhat.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