linux-kernel - [PATCH] KVM: X86: eliminate some meaningless code

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Date:   Fri, 21 Feb 2020 22:05:26 +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: eliminate some meaningless code

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

When kvm_vcpu_ioctl_get_cpuid2() fails, we set cpuid->nent to the value of
vcpu->arch.cpuid_nent. But this is in vain as cpuid->nent is not copied to
userspace by copy_to_user() from call site. Get rid of this meaningless
assignment and further cleanup the var r and out jump label.

On the other hand, when kvm_vcpu_ioctl_get_cpuid2() succeeds, we do not
change the content of struct cpuid. We can avoid copy_to_user() from call
site as struct cpuid remain unchanged.

Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
---
 arch/x86/kvm/cpuid.c | 14 ++++----------
 arch/x86/kvm/x86.c   |  6 ------
 2 files changed, 4 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index b1c469446b07..b83cedc63328 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -265,20 +265,14 @@ int kvm_vcpu_ioctl_get_cpuid2(struct kvm_vcpu *vcpu,
 			      struct kvm_cpuid2 *cpuid,
 			      struct kvm_cpuid_entry2 __user *entries)
 {
-	int r;
-
-	r = -E2BIG;
 	if (cpuid->nent < vcpu->arch.cpuid_nent)
-		goto out;
-	r = -EFAULT;
+		return -E2BIG;
+
 	if (copy_to_user(entries, &vcpu->arch.cpuid_entries,
 			 vcpu->arch.cpuid_nent * sizeof(struct kvm_cpuid_entry2)))
-		goto out;
-	return 0;
+		return -EFAULT;
 
-out:
-	cpuid->nent = vcpu->arch.cpuid_nent;
-	return r;
+	return 0;
 }
 
 static __always_inline void cpuid_mask(u32 *word, int wordnum)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fbabb2f06273..683c54e7be36 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4295,12 +4295,6 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 			goto out;
 		r = kvm_vcpu_ioctl_get_cpuid2(vcpu, &cpuid,
 					      cpuid_arg->entries);
-		if (r)
-			goto out;
-		r = -EFAULT;
-		if (copy_to_user(cpuid_arg, &cpuid, sizeof(cpuid)))
-			goto out;
-		r = 0;
 		break;
 	}
 	case KVM_GET_MSRS: {
-- 
2.19.1