In VMX, before we bring down a CPU we must VMCLEAR all VMCSs loaded on it
because (at least in theory) the processor might not have written all of its
content back to memory. Since a patch from June 26, 2008, this is done using
a per-cpu "vcpus_on_cpu" linked list of vcpus loaded on each CPU.
The problem is that with nested VMX, we no longer have the concept of a
vcpu being loaded on a cpu: A vcpu has multiple VMCSs (one for L1, others for
each L2), and each of those may be have been last loaded on a different cpu.
This trivial patch changes the code to keep on vcpus_on_cpu only L1 VMCSs.
This fixes crashes on L1 shutdown caused by incorrectly maintaing the linked
lists.
It is not a complete solution, though. It doesn't flush the inactive L1 or L2
VMCSs loaded on a CPU which is being shutdown. Doing this correctly will
probably require replacing the vcpu linked list by a link list of "saved_vcms"
objects (VMCS, cpu and launched), and it is left as a TODO.
Signed-off-by: Nadav Har'El <n...@il.ibm.com>
---
arch/x86/kvm/vmx.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
--- .before/arch/x86/kvm/vmx.c 2011-05-08 10:43:18.000000000 +0300
+++ .after/arch/x86/kvm/vmx.c 2011-05-08 10:43:18.000000000 +0300
@@ -638,7 +638,9 @@ static void __vcpu_clear(void *arg)
vmcs_clear(vmx->vmcs);
if (per_cpu(current_vmcs, cpu) == vmx->vmcs)
per_cpu(current_vmcs, cpu) = NULL;
- list_del(&vmx->local_vcpus_link);
+ /* TODO: currently, local_vcpus_link is just for L1 VMCSs */
+ if (!is_guest_mode(&vmx->vcpu))
+ list_del(&vmx->local_vcpus_link);
vmx->vcpu.cpu = -1;
vmx->launched = 0;
}
@@ -1100,8 +1102,10 @@ static void vmx_vcpu_load(struct kvm_vcp
kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
local_irq_disable();
- list_add(&vmx->local_vcpus_link,
- &per_cpu(vcpus_on_cpu, cpu));
+ /* TODO: currently, local_vcpus_link is just for L1 VMCSs */
+ if (!is_guest_mode(&vmx->vcpu))
+ list_add(&vmx->local_vcpus_link,
+ &per_cpu(vcpus_on_cpu, cpu));
local_irq_enable();
/*
@@ -1806,7 +1810,9 @@ static void vmclear_local_vcpus(void)
list_for_each_entry_safe(vmx, n, &per_cpu(vcpus_on_cpu, cpu),
local_vcpus_link)
- __vcpu_clear(vmx);
+ /* TODO: currently, local_vcpus_link is just for L1 VMCSs */
+ if (!is_guest_mode(&vmx->vcpu))
+ __vcpu_clear(vmx);
}
--
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