linux-kernel - [PATCH] KVM: x86/mmu: optimizing the code in mmu_try_to_unsync

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Date:   Fri, 20 May 2022 14:09:07 +0800
From:   Yun Lu <luyun_611@....com>
To:     pbonzini@...hat.com
Cc:     seanjc@...gle.com, vkuznets@...hat.com, wanpengli@...cent.com,
        jmattson@...gle.com, joro@...tes.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] KVM: x86/mmu: optimizing the code in mmu_try_to_unsync_pages

There is no need to check can_unsync and prefetch in the loop
every time, just move this check before the loop.

Signed-off-by: Yun Lu <luyun@...inos.cn>
---
 arch/x86/kvm/mmu/mmu.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 311e4e1d7870..e51e7735adca 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2534,6 +2534,12 @@ int mmu_try_to_unsync_pages(struct kvm *kvm, const struct kvm_memory_slot *slot,
 	if (kvm_slot_page_track_is_active(kvm, slot, gfn, KVM_PAGE_TRACK_WRITE))
 		return -EPERM;
 
+	if (!can_unsync)
+		return -EPERM;
+
+	if (prefetch)
+		return -EEXIST;
+
 	/*
 	 * The page is not write-tracked, mark existing shadow pages unsync
 	 * unless KVM is synchronizing an unsync SP (can_unsync = false).  In
@@ -2541,15 +2547,9 @@ int mmu_try_to_unsync_pages(struct kvm *kvm, const struct kvm_memory_slot *slot,
 	 * allowing shadow pages to become unsync (writable by the guest).
 	 */
 	for_each_gfn_indirect_valid_sp(kvm, sp, gfn) {
-		if (!can_unsync)
-			return -EPERM;
-
 		if (sp->unsync)
 			continue;
 
-		if (prefetch)
-			return -EEXIST;
-
 		/*
 		 * TDP MMU page faults require an additional spinlock as they
 		 * run with mmu_lock held for read, not write, and the unsync
-- 
2.25.1


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