On Thu, May 23, 2013 at 03:55:58AM +0800, Xiao Guangrong wrote:
> It is only used to zap the obsolete page. Since the obsolete page
> will not be used, we need not spend time to find its unsync children
> out. Also, we delete the page from shadow page cache so that the page
> is completely isolated after call this function.
>
> The later patch will use it to collapse tlb flushes
>
> Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
> ---
> arch/x86/kvm/mmu.c | 46 +++++++++++++++++++++++++++++++++++++++++-----
> 1 files changed, 41 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 9b57faa..e676356 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -1466,7 +1466,7 @@ static inline void kvm_mod_used_mmu_pages(struct kvm *kvm, int nr)
> static void kvm_mmu_free_page(struct kvm_mmu_page *sp)
> {
> ASSERT(is_empty_shadow_page(sp->spt));
> - hlist_del(&sp->hash_link);
> + hlist_del_init(&sp->hash_link);
> list_del(&sp->link);
> free_page((unsigned long)sp->spt);
> if (!sp->role.direct)
> @@ -2069,14 +2069,19 @@ static int mmu_zap_unsync_children(struct kvm *kvm,
> return zapped;
> }
>
> -static int kvm_mmu_prepare_zap_page(struct kvm *kvm, struct kvm_mmu_page *sp,
> - struct list_head *invalid_list)
> +static int
> +__kvm_mmu_prepare_zap_page(struct kvm *kvm, struct kvm_mmu_page *sp,
> + bool zap_unsync_children,
> + struct list_head *invalid_list)
> {
> - int ret;
> + int ret = 0;
>
> trace_kvm_mmu_prepare_zap_page(sp);
> ++kvm->stat.mmu_shadow_zapped;
> - ret = mmu_zap_unsync_children(kvm, sp, invalid_list);
> +
> + if (likely(zap_unsync_children))
> + ret = mmu_zap_unsync_children(kvm, sp, invalid_list);
> +
Why is this an important case to be optimized?
1) shadow is the uncommon, obsolete case.
2) mmu_zap_unsync_children has
if (parent->role.level == PT_PAGE_TABLE_LEVEL)
return 0;
So the large majority of pages are already optimized.
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