[PATCH v8 11/11] KVM: MMU: reduce KVM_REQ_MMU_RELOAD when root page is zapped

[Xiao Guangrong]

From: Gleb Natapov <gleb@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
---
 arch/x86/kvm/mmu.c |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 79af88a..6941fa7 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;
-- 
1.7.7.6

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