linux-kernel - [PATCH 1/3] KVM: VMX: Drop explicit zeroing of MSR guest values at vCPU creation

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Date:   Tue, 14 Sep 2021 16:08:38 -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, Reiji Watanabe <reijiw@...gle.com>
Subject: [PATCH 1/3] KVM: VMX: Drop explicit zeroing of MSR guest values at
 vCPU creation

Don't zero out user return and nested MSRs during vCPU creation, and
instead rely on vcpu_vmx being zero-allocated.  Explicitly zeroing MSRs
is not wrong, and is in fact necessary if KVM ever emulates vCPU RESET
outside of vCPU creation, but zeroing only a subset of MSRs is confusing.

Poking directly into KVM's backing is also undesirable in that it doesn't
scale and is error prone.  Ideally KVM would have a common RESET path for
all MSRs, e.g. by expanding kvm_set_msr(), which would obviate the need
for this out-of-bad code (to support standalone RESET).

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/vmx.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index fada1055f325..dc274b4c9912 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6818,10 +6818,8 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu)
 			goto free_vpid;
 	}
 
-	for (i = 0; i < kvm_nr_uret_msrs; ++i) {
-		vmx->guest_uret_msrs[i].data = 0;
+	for (i = 0; i < kvm_nr_uret_msrs; ++i)
 		vmx->guest_uret_msrs[i].mask = -1ull;
-	}
 	if (boot_cpu_has(X86_FEATURE_RTM)) {
 		/*
 		 * TSX_CTRL_CPUID_CLEAR is handled in the CPUID interception.
@@ -6878,8 +6876,6 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu)
 
 	if (nested)
 		memcpy(&vmx->nested.msrs, &vmcs_config.nested, sizeof(vmx->nested.msrs));
-	else
-		memset(&vmx->nested.msrs, 0, sizeof(vmx->nested.msrs));
 
 	vcpu_setup_sgx_lepubkeyhash(vcpu);
 
-- 
2.33.0.309.g3052b89438-goog