KVM: MMU: reduce KVM_REQ_MMU_RELOAD when root page is zapped

Quote Gleb's mail:
| why don't we check for sp->role.invalid in
| kvm_mmu_prepare_zap_page before calling kvm_reload_remote_mmus()?

and

| Actually we can add check for is_obsolete_sp() there too since
| kvm_mmu_invalidate_all_pages() already calls kvm_reload_remote_mmus()
| after incrementing mmu_valid_gen.

[ Xiao: add some comments and the check of is_obsolete_sp() ]

Signed-off-by: Gleb Natapov <gleb@redhat.com>
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, 7 insertions, 1 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 79af88ab2f1d..6941fa74eb35 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2108,7 +2108,13 @@ static int kvm_mmu_prepare_zap_page(struct kvm *kvm, struct kvm_mmu_page *sp,
                 kvm_mod_used_mmu_pages(kvm, -1);
         } else {
                 list_move(&sp->link, &kvm->arch.active_mmu_pages);
-                kvm_reload_remote_mmus(kvm);
+
+                /*
+                 * The obsolete pages can not be used on any vcpus.
+                 * See the comments in kvm_mmu_invalidate_zap_all_pages().
+                 */
+                if (!sp->role.invalid && !is_obsolete_sp(kvm, sp))
+                        kvm_reload_remote_mmus(kvm);
         }
 
         sp->role.invalid = 1;