linux-kernel - [PATCH 4/4] KVM: x86/mmu: Topup pte_list

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Date:   Fri, 24 Jun 2022 23:27:35 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Peter Xu <peterx@...hat.com>
Subject: [PATCH 4/4] KVM: x86/mmu: Topup pte_list_desc cache iff VM is using rmaps

Topup the per-vCPU pte_list_desc caches if and only if the VM is using
rmaps, i.e. KVM is not using the TDP MMU or KVM is shadowing a nested TDP
MMU.  This avoids wasting 1280 bytes per vCPU when KVM is using the TDP
MMU and L1 is not utilizing nested TDP.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/mmu/mmu.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 2db328d28b7b..fcbdd780075f 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -646,11 +646,13 @@ static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu, bool maybe_indirect)
 {
 	int r;
 
-	/* 1 rmap, 1 parent PTE per level, and the prefetched rmaps. */
-	r = kvm_mmu_topup_memory_cache(&vcpu->arch.mmu_pte_list_desc_cache,
-				       1 + PT64_ROOT_MAX_LEVEL + PTE_PREFETCH_NUM);
-	if (r)
-		return r;
+	if (kvm_memslots_have_rmaps(vcpu->kvm)) {
+		/* 1 rmap, 1 parent PTE per level, and the prefetched rmaps. */
+		r = kvm_mmu_topup_memory_cache(&vcpu->arch.mmu_pte_list_desc_cache,
+					       1 + PT64_ROOT_MAX_LEVEL + PTE_PREFETCH_NUM);
+		if (r)
+			return r;
+	}
 	r = kvm_mmu_topup_memory_cache(&vcpu->arch.mmu_shadow_page_cache,
 				       PT64_ROOT_MAX_LEVEL);
 	if (r)
-- 
2.37.0.rc0.161.g10f37bed90-goog