Subject: Re: [PATCH v6 42/44] KVM: VMX: Dedup code for adding MSR to VMCS's auto list

From: Namhyung Kim <[email-masked]>
Date: Thu, 19 Feb 2026 11:31:18 -0800

Hello,

On Fri, Dec 05, 2025 at 04:17:18PM -0800, Sean Christopherson wrote:
> Add a helper to add an MSR to a VMCS's "auto" list to deduplicate the code
> in add_atomic_switch_msr(), and so that the functionality can be used in
> the future for managing the MSR auto-store list.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <[email-masked]>
> ---
>  arch/x86/kvm/vmx/vmx.c | 41 +++++++++++++++++++----------------------
>  1 file changed, 19 insertions(+), 22 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 018e01daab68..3f64d4b1b19c 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1093,12 +1093,28 @@ static __always_inline void add_atomic_switch_msr_special(struct vcpu_vmx *vmx,
>  	vm_exit_controls_setbit(vmx, exit);
>  }
>  
> +static void vmx_add_auto_msr(struct vmx_msrs *m, u32 msr, u64 value,
> +			     unsigned long vmcs_count_field, struct kvm *kvm)
> +{
> +	int i;
> +
> +	i = vmx_find_loadstore_msr_slot(m, msr);
> +	if (i < 0) {
> +		if (KVM_BUG_ON(m->nr == MAX_NR_LOADSTORE_MSRS, kvm))
> +			return;
> +
> +		i = m->nr++;
> +		m->val[i].index = msr;
> +		vmcs_write32(vmcs_count_field, m->nr);
> +	}
> +	m->val[i].value = value;
> +}
> +
>  static void add_atomic_switch_msr(struct vcpu_vmx *vmx, unsigned msr,
>  				  u64 guest_val, u64 host_val)
>  {
>  	struct msr_autoload *m = &vmx->msr_autoload;
>  	struct kvm *kvm = vmx->vcpu.kvm;
> -	int i;
>  
>  	switch (msr) {
>  	case MSR_EFER:
> @@ -1132,27 +1148,8 @@ static void add_atomic_switch_msr(struct vcpu_vmx *vmx, unsigned msr,
>  		wrmsrq(MSR_IA32_PEBS_ENABLE, 0);
>  	}
>  
> -	i = vmx_find_loadstore_msr_slot(&m->guest, msr);
> -	if (i < 0) {
> -		if (KVM_BUG_ON(m->guest.nr == MAX_NR_LOADSTORE_MSRS, kvm))
> -			return;
> -
> -		i = m->guest.nr++;
> -		m->guest.val[i].index = msr;
> -		vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, m->guest.nr);
> -	}
> -	m->guest.val[i].value = guest_val;
> -
> -	i = vmx_find_loadstore_msr_slot(&m->host, msr);
> -	if (i < 0) {
> -		if (KVM_BUG_ON(m->host.nr == MAX_NR_LOADSTORE_MSRS, kvm))
> -			return;
> -
> -		i = m->host.nr++;
> -		m->host.val[i].index = msr;
> -		vmcs_write32(VM_EXIT_MSR_LOAD_COUNT, m->host.nr);
> -	}
> -	m->host.val[i].value = host_val;
> +	vmx_add_auto_msr(&m->guest, msr, guest_val, VM_ENTRY_MSR_LOAD_COUNT, kvm);
> +	vmx_add_auto_msr(&m->guest, msr, host_val, VM_EXIT_MSR_LOAD_COUNT, kvm);

Shouldn't it be &m->host for the host_val?

Thanks,
Namhyung

>  }
>  
>  static bool update_transition_efer(struct vcpu_vmx *vmx)
> -- 
> 2.52.0.223.gf5cc29aaa4-goog
>