KVM: MMU: fast invalidate all pages

The current kvm_mmu_zap_all is really slow - it is holding mmu-lock to
walk and zap all shadow pages one by one, also it need to zap all guest
page's rmap and all shadow page's parent spte list. Particularly, things
become worse if guest uses more memory or vcpus. It is not good for
scalability

In this patch, we introduce a faster way to invalidate all shadow pages.
KVM maintains a global mmu invalid generation-number which is stored in
kvm->arch.mmu_valid_gen and every shadow page stores the current global
generation-number into sp->mmu_valid_gen when it is created

When KVM need zap all shadow pages sptes, it just simply increase the
global generation-number then reload root shadow pages on all vcpus.
Vcpu will create a new shadow page table according to current kvm's
generation-number. It ensures the old pages are not used any more.
Then the obsolete pages (sp->mmu_valid_gen != kvm->arch.mmu_valid_gen)
are zapped by using lock-break technique

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 3741c653767c..bff7d464a6ae 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -222,6 +222,7 @@ struct kvm_mmu_page {
         int root_count;          /* Currently serving as active root */
         unsigned int unsync_children;
         unsigned long parent_ptes;      /* Reverse mapping for parent_pte */
+        unsigned long mmu_valid_gen;
         DECLARE_BITMAP(unsync_child_bitmap, 512);
 
 #ifdef CONFIG_X86_32
@@ -529,6 +530,7 @@ struct kvm_arch {
         unsigned int n_requested_mmu_pages;
         unsigned int n_max_mmu_pages;
         unsigned int indirect_shadow_pages;
+        unsigned long mmu_valid_gen;
         struct hlist_head mmu_page_hash[KVM_NUM_MMU_PAGES];
         /*
          * Hash table of struct kvm_mmu_page.