Sean Christopherson <seanjc@xxxxxxxxxx> writes:
> 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).
Just thinking out loud: we can probably enhance KVM_SET_MSRS making it
possible for userspace VMM to set the default (as not every setting need
to survive RESET). Conveniently enough, 'struct kvm_msr_entry' has 32
bits reserved and we can bite off one for 'default' flag.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
> 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 d44d07d5a02f..8d14066db3ea 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6819,10 +6819,8 @@ 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.
> @@ -6879,8 +6877,6 @@ 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);
Reviewed-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
--
Vitaly
