linux-kernel - [RFC PATCH 1/5] KVM: Split tdp_mmu_pages to private and shared lists

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Message-ID: <20230407201921.2703758-2-sagis@google.com>
Date:   Fri,  7 Apr 2023 20:19:17 +0000
From:   Sagi Shahar <sagis@...gle.com>
To:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Isaku Yamahata <isaku.yamahata@...el.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Kai Huang <kai.huang@...el.com>,
        Zhi Wang <zhi.wang.linux@...il.com>,
        Chao Peng <chao.p.peng@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sagi Shahar <sagis@...gle.com>
Subject: [RFC PATCH 1/5] KVM: Split tdp_mmu_pages to private and shared lists

tdp_mmu_pages holds all the active pages used by the mmu. When we
transfer the state during intra-host migration we need to transfer the
private pages but not the shared ones.

Keeping them in separate counters makes this transfer more efficient.

Signed-off-by: Sagi Shahar <sagis@...gle.com>
---
 arch/x86/include/asm/kvm_host.h |  5 ++++-
 arch/x86/kvm/mmu/tdp_mmu.c      | 11 +++++++++--
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index ae377eec81987..5ed70cd9d74bf 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1426,9 +1426,12 @@ struct kvm_arch {
 	struct task_struct *nx_huge_page_recovery_thread;
 
 #ifdef CONFIG_X86_64
-	/* The number of TDP MMU pages across all roots. */
+	/* The number of non-private TDP MMU pages across all roots. */
 	atomic64_t tdp_mmu_pages;
 
+	/* Same as tdp_mmu_pages but only for private pages. */
+	atomic64_t tdp_private_mmu_pages;
+
 	/*
 	 * List of struct kvm_mmu_pages being used as roots.
 	 * All struct kvm_mmu_pages in the list should have
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 58a236a69ec72..327dee4f6170e 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -44,6 +44,7 @@ void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm)
 	destroy_workqueue(kvm->arch.tdp_mmu_zap_wq);
 
 	WARN_ON(atomic64_read(&kvm->arch.tdp_mmu_pages));
+	WARN_ON(atomic64_read(&kvm->arch.tdp_private_mmu_pages));
 	WARN_ON(!list_empty(&kvm->arch.tdp_mmu_roots));
 
 	/*
@@ -373,13 +374,19 @@ static void handle_changed_spte_dirty_log(struct kvm *kvm, int as_id, gfn_t gfn,
 static void tdp_account_mmu_page(struct kvm *kvm, struct kvm_mmu_page *sp)
 {
 	kvm_account_pgtable_pages((void *)sp->spt, +1);
-	atomic64_inc(&kvm->arch.tdp_mmu_pages);
+	if (is_private_sp(sp))
+		atomic64_inc(&kvm->arch.tdp_private_mmu_pages);
+	else
+		atomic64_inc(&kvm->arch.tdp_mmu_pages);
 }
 
 static void tdp_unaccount_mmu_page(struct kvm *kvm, struct kvm_mmu_page *sp)
 {
 	kvm_account_pgtable_pages((void *)sp->spt, -1);
-	atomic64_dec(&kvm->arch.tdp_mmu_pages);
+	if (is_private_sp(sp))
+		atomic64_dec(&kvm->arch.tdp_private_mmu_pages);
+	else
+		atomic64_dec(&kvm->arch.tdp_mmu_pages);
 }
 
 /**
-- 
2.40.0.348.gf938b09366-goog