linux-kernel - [PATCH 3/3] KVM: x86/mmu: Move lpage_disallowed_link further "down" in kvm_mmu

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Message-Id: <20210901221023.1303578-4-seanjc@google.com>
Date:   Wed,  1 Sep 2021 15:10:23 -0700
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, Jia He <justin.he@....com>
Subject: [PATCH 3/3] KVM: x86/mmu: Move lpage_disallowed_link further "down"
 in kvm_mmu_page

Move "lpage_disallowed_link" out of the first 64 bytes, i.e. out of the
first cache line, of kvm_mmu_page so that "spt" and to a lesser extent
"gfns" land in the first cache line.  "lpage_disallowed_link" is accessed
relatively infrequently compared to "spt", which is accessed any time KVM
is walking and/or manipulating the shadow page tables.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/mmu/mmu_internal.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index 4b06e6040e90..cae932afc8d3 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -31,9 +31,12 @@ extern bool dbg;
 #define IS_VALID_PAE_ROOT(x)	(!!(x))
 
 struct kvm_mmu_page {
+	/*
+	 * Note, "link" through "spt" fit in a single 64 byte cache line on
+	 * 64-bit kernels, keep it that way unless there's a reason not to.
+	 */
 	struct list_head link;
 	struct hlist_node hash_link;
-	struct list_head lpage_disallowed_link;
 
 	bool tdp_mmu_page;
 	bool unsync;
@@ -59,6 +62,7 @@ struct kvm_mmu_page {
 	struct kvm_rmap_head parent_ptes; /* rmap pointers to parent sptes */
 	DECLARE_BITMAP(unsync_child_bitmap, 512);
 
+	struct list_head lpage_disallowed_link;
 #ifdef CONFIG_X86_32
 	/*
 	 * Used out of the mmu-lock to avoid reading spte values while an
-- 
2.33.0.153.gba50c8fa24-goog