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([2001:b07:6468:f312:b8fe:679e:87eb:c059]) by smtp.gmail.com with ESMTPSA id n16sm2747662wro.88.2020.01.23.04.15.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 23 Jan 2020 04:15:35 -0800 (PST) Subject: Re: [PATCH] KVM: x86: avoid some unnecessary copy in __x86_set_memory_region() To: linmiaohe , rkrcmar@redhat.com, sean.j.christopherson@intel.com, vkuznets@redhat.com, wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org References: <1579748413-432-1-git-send-email-linmiaohe@huawei.com> From: Paolo Bonzini Message-ID: <2cb1c43c-932e-d587-bc0d-5d433649abb1@redhat.com> Date: Thu, 23 Jan 2020 13:15:32 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <1579748413-432-1-git-send-email-linmiaohe@huawei.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 23/01/20 04:00, linmiaohe wrote: > From: Miaohe Lin > > 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. The compiler should be able to do this change, so I prefer to keep the old code. Also, moving the assignments inside the "if" risks causing uninitialized variable warnings, even though indeed they are only used if size == 0. Thanks, Paolo > No functional change intended. > > Signed-off-by: Miaohe Lin > --- > 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; > } >