Re: [PATCH: kvm 4/5] Fix hotremove of CPUs for KVM.

Avi Kivity
2009-09-27T08:54:43Z

On 09/25/2009 03:47 AM, Zachary Amsden wrote:
> In the process of bringing down CPUs, the SVM / VMX structures associated
> with those CPUs are not freed. This may cause leaks when unloading and
> reloading the KVM module, as only the structures associated with online
> CPUs are cleaned up. So, clean up all possible CPUs, not just online ones.
>
> Signed-off-by: Zachary Amsden<zamsden@redhat.com>
> ---
> arch/x86/kvm/svm.c | 2 +-
> arch/x86/kvm/vmx.c | 7 +++++--
> 2 files changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 8f99d0c..13ca268 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -525,7 +525,7 @@ static __exit void svm_hardware_unsetup(void)
> {
> int cpu;
>
> - for_each_online_cpu(cpu)
> + for_each_possible_cpu(cpu)
> svm_cpu_uninit(cpu);
>
> __free_pages(pfn_to_page(iopm_base>> PAGE_SHIFT), IOPM_ALLOC_ORDER);
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index b8a8428..603bde3 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -1350,8 +1350,11 @@ static void free_kvm_area(void)
> {
> int cpu;
>
> - for_each_online_cpu(cpu)
> - free_vmcs(per_cpu(vmxarea, cpu));
> + for_each_possible_cpu(cpu)
> + if (per_cpu(vmxarea, cpu)) {
> + free_vmcs(per_cpu(vmxarea, cpu));
> + per_cpu(vmxarea, cpu) = NULL;
> + }
> }
>
> static __init int alloc_kvm_area(void)
>

First, I'm not sure per_cpu works for possible but not actual cpus.
Second, we now eagerly allocate but lazily free, leading to lots of ifs
and buts. I think the code can be cleaner by eagerly allocating and
eagerly freeing.

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.