Re: [PATCH] do not free active mmu pages in free_mmu_pages()

Marcelo Tosatti
2009-03-16T20:16:49Z

On Wed, Mar 11, 2009 at 12:07:55PM +0200, Gleb Natapov wrote:
> free_mmu_pages() should only undo what alloc_mmu_pages() does.
>
> Signed-off-by: Gleb Natapov <gleb@redhat.com>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 2a36f7f..b625ed4 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -2638,14 +2638,6 @@ EXPORT_SYMBOL_GPL(kvm_disable_tdp);
>
> static void free_mmu_pages(struct kvm_vcpu *vcpu)
> {
> - struct kvm_mmu_page *sp;
> -
> - while (!list_empty(&vcpu->kvm->arch.active_mmu_pages)) {
> - sp = container_of(vcpu->kvm->arch.active_mmu_pages.next,
> - struct kvm_mmu_page, link);
> - kvm_mmu_zap_page(vcpu->kvm, sp);
> - cond_resched();
> - }
> free_page((unsigned long)vcpu->arch.mmu.pae_root);
> }

Doesnt the vm shutdown path rely on the while loop you removed to free
all shadow pages before freeing the mmu kmem caches, if mmu notifiers
is disabled?

And how harmful is that loop? Zaps the entire cache on cpu hotunplug?