linux-kernel - [PATCH] KVM: x86: avoid some unnecessary copy in __x86_set_memory

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Date:   Thu, 23 Jan 2020 11:00:13 +0800
From:   linmiaohe <linmiaohe@...wei.com>
To:     <pbonzini@...hat.com>, <rkrcmar@...hat.com>,
        <sean.j.christopherson@...el.com>, <vkuznets@...hat.com>,
        <wanpengli@...cent.com>, <jmattson@...gle.com>, <joro@...tes.org>,
        <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
        <hpa@...or.com>
CC:     <linmiaohe@...wei.com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <x86@...nel.org>
Subject: [PATCH] KVM: x86: avoid some unnecessary copy in __x86_set_memory_region()

From: Miaohe Lin <linmiaohe@...wei.com>

Only userspace_addr and npages are passed to vm_munmap() when remove a
memory region. So we shouldn't copy the integral kvm_memory_slot struct.

No functional change intended.

Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
---
 arch/x86/kvm/x86.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d1faa74981d9..767f29877938 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9735,9 +9735,9 @@ void kvm_arch_sync_events(struct kvm *kvm)
 int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size)
 {
 	int i, r;
-	unsigned long hva;
+	unsigned long hva, uaddr, npages;
 	struct kvm_memslots *slots = kvm_memslots(kvm);
-	struct kvm_memory_slot *slot, old;
+	struct kvm_memory_slot *slot;
 
 	/* Called with kvm->slots_lock held.  */
 	if (WARN_ON(id >= KVM_MEM_SLOTS_NUM))
@@ -9761,9 +9761,10 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size)
 			return 0;
 
 		hva = 0;
+		uaddr = slot->userspace_addr;
+		npages = slot->npages;
 	}
 
-	old = *slot;
 	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
 		struct kvm_userspace_memory_region m;
 
@@ -9778,7 +9779,7 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size)
 	}
 
 	if (!size)
-		vm_munmap(old.userspace_addr, old.npages * PAGE_SIZE);
+		vm_munmap(uaddr, npages * PAGE_SIZE);
 
 	return 0;
 }
-- 
2.19.1