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

Sean Christopherson
2021-09-14T23:09:26Z

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@google.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